AFB Engine Overview (Solution)

Below is a collection of known issues and solutions.
Regarding the AFB engine: This list covers all models and vehicle types in which this engine was installed.



Dynamically check injection start

Read measurement block display group 07, engine idling.

Coolant target temperature: at least 85°C.

Initiate basic setting for display group 04, engine idling.

Display setting on the system: default value is 4.
850/min late 1.5 5 min overtime 100%

Field 4: Setpoint: 100%.
Field 2: Setpoint: "late".
Field 3: Setpoint: 2 °C ± 2 °.



Humming -/ Roaring noises between 1400 and 2000 RPM

Loud rumbling/throbbing noises accompanied by vibrations felt in the seat when accelerating in the higher gears. The engine speed is between 1400-2000 RPM. The engine is running unevenly, and the automatic transmission is in limp mode.

Cause:

1. Tensioner roller for the timing belt on the camshaft drive is difficult to turn, seized, or the timing belt tensioning element is defective. This can cause deviations in the valve timing. In extreme cases, this can result in error code 00550: "Injection start control - regulation difference in the engine control unit." In vehicles with automatic transmissions, this can trigger the transmission to enter limp-home mode.

Performance variations between individual cylinders lead to discrepancies in injection volumes during idle speed control, which in turn cause undesirable resonance vibrations.

Solution:
1. Remove the timing belt tensioner roller and check its smooth operation on the mounting bolt; replace if necessary. Check the timing belt tensioner mechanism to see if it can be compressed. The timing belt tensioner is oil-damped and should only compress slowly with even pressure. The timing belt tensioner mechanism must automatically extend; replace if necessary.



Error 18047 / 00777 in the engine control unit (ECU).

The engine is running at a higher-than-normal idle speed and is not responding to acceleration.
Error code 18047 or 00777 (throttle position sensor) is stored in the engine control unit.

Cause:
The respective resistance values of the throttle position sensor are not being transmitted correctly to the engine control unit. Since there are no other components involved in the direct wiring between the throttle position sensor and the engine control unit, the following causes could potentially be responsible for this error code:
- faulty throttle position sensor.
- faulty connection
- Moisture on electrical contacts.
Even if the engine control unit only temporarily fails to recognize the accelerator pedal position, a limp-home mode is activated for safety reasons. This manifests in TDI engines as an increased idle speed.

Solution:
Test the accelerator pedal module/sensor. If it is functioning correctly, the fault should be located in the wiring connections. If no faults can be found here either, all connectors between the accelerator pedal module and the engine control unit, especially those of the clutch interface in the fuse box, must be checked for secure contact.

Sure, here is the translation of the text from German to English:

"Note:"
Coolant can leak through the engine wiring harness to the electronic control unit (ECU) and even to the motor control module if there is a faulty coolant level sensor in the expansion tank or a defective coolant temperature sensor. In this case, the respective sensor and the entire engine wiring harness need to be replaced.



Low heating power / Particles in the cooling system

All engines feature a gray cast iron cylinder crankcase.
Heating performance is too low, coolant is rust-colored, and there are particles in the cooling system.

Cause:
Due to corrosion in the cooling circuit of the engine crankcase, the coolant turns a rusty brown color. Particles accumulate in the coolant reservoir, and the heater core becomes clogged.

Solution:
To permanently eliminate the defect, the cooling system must be flushed using a special cleaning additive as follows:

The rinsing additive can be ordered under the product number G 111 000 A3. If the heating performance is impaired (due to a clogged heat exchanger), the heating performance must be measured before the first rinse cycle. This is the only way to monitor the effectiveness of the cleaning process.

Prerequisites for the exam:

• Engine is warm.
• Speed is approximately 2000 RPM.
• Select the highest temperature setting.

1. Measurement of heating power.
- Adjust air distribution on switchgear nozzles.
- Insert the thermocouple into the central nozzle to a depth of approximately 5 cm. Perform the measurement for about 5 minutes and record the value.

2. Flush the cylinder crankcase.
- Completely drain the coolant (important).
- Remove the coolant thermostat and seal the cooling system for operation.
- Add the rinsing agent via the balancing tank (1.5 to 2.0 liters of rinsing agent per rinse cycle).
- Fill and bleed the cooling system with verschandeln tap water (drinking water quality) according to regulations.
- Close storage containers.
- Start the engine and operate or drive it at slightly elevated RPM for 20 minutes until it reaches operating temperature.
- Drain the cooling system again. Be careful of hot rinsing fluid.

• The rinsing process should be repeated at least once, and if necessary, twice, as described above.

3. Flush the heating heat exchanger.
- Reinstall the coolant thermostat.
- Repeat the rinsing process as described in section -2, ensuring that the built-in coolant thermostat is still functioning.
- Repeat the measurement of heating power as described in section -1.

• If there is no improvement in heating performance, the heat exchanger may be so clogged that only a replacement will resolve the issue.

Did the flush improve the heating performance?
- Reinstall the coolant thermostat.
- To completely remove the cleaning solution from the cooling system, it is necessary to flush the system twice more with tap water for 5 minutes each time, without using the coolant thermostat.
- Reinstall the coolant thermostat and replace the expansion tank.
- Disconnect the coolant hoses in the engine compartment and check them for deposits.
- If there are significant deposits present, the coolant hoses must be replaced.
- Fill, bleed, top up, and seal the cooling system with coolant according to local regulations.


No clutch engagement in automatic transmission

The transmission control unit has a fault code indicating "gear monitoring, incorrect gear ratio," and the engine control unit has a fault code for "coolant temperature sensor G62, intermittent." It is possible that the automatic transmission is already experiencing engagement problems in gears 4 and 5.
Only automatic vehicles with a 2.5L TDI engine are affected.

Cause:
The coolant temperature sensor occasionally detects a much lower temperature (e.g., -4°C instead of 60°C). As a result, the engine control unit calculates a significantly low (incorrect) engine torque, which is transmitted via CAN bus to the transmission control unit for ATF pressure calculation (e.g., calculated: 20 Nm, actual: 190 Nm). The clutches are then held with insufficient pressure, causing them to slip. This primarily burns out clutch E, which is responsible for power transfer in gears 4 and 5.
The coolant temperature sensor is only recognized as faulty by the engine control unit if it detects an interruption or short circuit to the positive terminal. After restarting the engine, this error entry becomes a sporadic error, and damage to the transmission can begin again.

Solution:
Read the error codes from the engine and transmission control unit.
If the described errors are stored in the engine and transmission control unit, the coolant temperature sensor should be replaced, and the automatic transmission should be checked for proper engagement, especially in gears 4 and 5. To do this, disconnect the transmission control unit from the vehicle's wiring harness and perform a static brake speed test in drive (D) for a maximum of 5 seconds (the transmission will be in emergency mode in 4th gear). If the engine speed exceeds 2800/min, this indicates a slipping clutch.

Sure, here is the translation of the text from German to English:

"Note:"
When assessing the condition of the automatic transmission fluid (ATF), it must be considered that in diesel vehicles, the high stress on the torque converter clutch can cause the ATF to darken even with transmissions in good working order, especially after driving more than 20,000 km. The only way to definitively determine the ATF's condition is by comparing its smell ("burnt" or "not burnt") to that of new ATF.

After replacing the coolant temperature sensor in measurement block 009 of the transmission control unit, the engine torque must be checked for plausibility during driving operation to eliminate any potential additional sources of error. In full load operation, the torque should correspond to approximately the maximum torque documented in the technical specifications (±5%).

Sure, here is the translation of the text from German to English:

"Note:"
The coolant temperature displayed on the instrument cluster may not be identical to the value read by the engine control unit, as the coolant temperature sensor operates with two independent, temperature-dependent resistors.



Fuel line damaged during installation

Fuel leakage after installation and removal of the fuel line in the underbody area.

Cause:
The fuel line is protected from damage by a cover located in the underbody area. This cover is secured to the fuel lines by being clipped into place at the rear with retaining clips and fastened at the front with 2 screws on the wheel arch liner. The retaining clips on the cover are also fitted with a screw, which does not contribute to structural strength but solely supports the clamping function of the clips.

If this screw is removed during a repair and later reinstalled without being properly tightened, it can damage the fuel line.

Solution:
When disassembling the cover, it must only be removed by loosening the two mounting screws in the front wheel well and disconnecting it from the fuel lines at the rear. The pre-installed screw on the cover must not be removed.



Fuel leakage on the outside of the cylinder head

Cause:
In 4-valve TDI engines, the fuel injectors are necessarily routed vertically through the valve cover and cylinder head, thus being surrounded by engine oil. To prevent extreme oil dilution in case of defective or leaky injectors due to improper installation, horizontal drain holes are led from all injector housings outwards. Without these drain holes, the oil pan would quickly fill up in such a situation, potentially causing the engine to run uncontrollably.

Solution:
If diesel fuel leaks from any of the three bores located on the side of the cylinder head, it is due to a damaged O-ring in the corresponding injector. In this case, the injector must be replaced.



Coolant leak at the expansion tank

Cause:
Hose connection, vent hose - expansion tank not functioning correctly.
The connector housing for the coolant sensor on the expansion tank is leaking.
Due to a manufacturing defect, the mesh inside the coolant hose is loose. As a result, the coolant leaks out through the vent hose connection to the expansion tank due to capillary action.

Solution:
Replace the hose clamp.
Disconnect the coolant level sensor connector. If there are traces of coolant visible in the connector housing, replace the expansion tank.
If coolant leaks from the coolant hose fabric at the connection to the expansion tank, the coolant hose must be replaced.

Sure, here is the translation of the text from German to English:

"Note:"
Coolant traces on the seam of the expansion tank can have the following causes:
- Leak in the hose connection at the vent hose (see 1).
- Overfilling of the cooling system, causing coolant to be expelled through the filler cap of the expansion tank.
- The pressure relief valve in the lid is not maintaining the required pressure.



Loud noises from a timing belt drive

Loud noises coming from the timing belt drive; defective idler pulley for the timing belt.

Cause:
The idler pulley for the timing belt is shifting forward and rubbing against the vibration damper as a result.

Solution:
Replace the idler pulley for the timing belt drive, along with the timing belt and any potentially damaged adjacent components.
Only the idler pulley with part number 06C 109 244 D is permitted for installation.
The new redirecting roller is backward compatible.



Oil leak lines are leaking.

Fuel loss due to leaking oil lines that have become detached.

Cause:
The oil feed lines consist of a rubber hose that is reinforced with fabric for stability.
Due to embrittlement of the material and tearing of the rubber hose, the oil drain lines can become detached from the connections of the injector or the distributor injection pump.

Solution:
To prevent leaks from the oil lines, the following points must be strictly adhered to:

If a pipe needs to be disconnected for repair work, it must generally be replaced.
Repair attempts involving cutting and reattaching are not permitted. This is necessary because the removal process creates microscopic cracks that compromise the secure fit on the connector.
When replacing, only use the hoses specified in set number 059 198 998 B. Under no circumstances should lines that appear visually similar but have different part numbers be used.



Lack of performance

V6 TDI: Gradually decreasing engine power.
V6 TDI: Sudden loss of power in rainy conditions; possibly an error code 00553 (mass airflow sensor, implausible signal) stored in the engine control unit.

Cause:
Oil mist settles on the sensor membrane of the mass airflow sensor. The mass airflow signal becomes increasingly distorted, leading to a noticeable loss of power. If the "warm-up phase" of the mass airflow sensor, which lasts for 4 minutes after turning off the engine, is still active, the oil mist will additionally adhere to the membrane. This gradual change usually does not trigger any error messages.

Under heavy rain and at very high speeds, water splashed up by vehicles ahead can be sucked into the engine. In extreme cases, the air filter element becomes completely saturated, and water can reach the mass airflow sensor. This sudden change in signal causes a loss of power, potentially triggers an error code 00553, and puts the engine control unit into emergency mode.

Solution:
Check the mass airflow sensors. Compare the target and actual values of the air mass entering the engine in measurement block 10 under load. Replace the mass airflow sensors if the target values are not reached.

Using a voltmeter or test lamp, check at pin 2 of the mass airflow sensor to see if there is still voltage present after the engine has been switched off by turning off the ignition. If voltage is still present, as a preventative measure against further contamination of the mass airflow sensor, the "warm-up phase" must be interrupted, and the power supply to the mass airflow sensor should be connected directly to terminal 15 (ignition).

Procedure: Type A6.
1. Disconnect the wire from pin 2 of the mass airflow sensor, cut the contact, and insulate the cable. The connector is numbered.
2. Run a new cable with an insulating tube (cross-section 1 sq mm) and a 2.8 mm gold contact, along with single-wire sealing, from pin 2 of the mass airflow sensor to the output of fuse 31 in the central electrical unit. (Fuse 31 = reversing lights = terminal 15). Route the cable along the engine wiring harness, through existing rubber grommets, into the water reservoir and then into the electrical box.
3. Turn on the ignition. There should be approximately battery voltage at pin 2 of the mass airflow sensor. Start the engine. After turning off the engine by switching off the ignition, there should be no voltage at pin 2 anymore. Supplying direct voltage does not affect the driving behavior; it is purely a preventative measure against recontamination.

Check the air filter element for water ingress. If water has been drawn in, replace the air filter element. Bosch mass airflow sensors (with a black plastic housing) must be replaced with a new Bosch part after contact with water and if a negative result is obtained during testing in data block 10. Hitachi mass airflow sensors (with an aluminum housing) typically do not need to be replaced after contact with water, provided that a test drive can be completed without any issues.

It is not possible to interchange air mass flow sensor units between different models.
As a preventative measure and to avoid recurring issues (water intake), the following parts (Nordland version) can be installed:
Air filter lower section with snow deflector, part number 4B0 133 837 F.
Air intake snorkel with coarse mesh grille, part number 4B0 129 617 F.

Below the air filter is a circular opening in the bodywork that leads to the wheel well. The fuel lines pass through this opening. To prevent water from being sucked into the air filter via this opening, it must be sealed with suitable material (such as foam).



Performance Deficiency II

Sudden performance drop, error code 00575 (intake manifold pressure) stored in the engine control unit's fault memory.

Cause:
If the engine control unit detects a too-low or too-high intake manifold pressure (boost pressure), it switches to a limp mode, and the engine power is significantly reduced by adjusting the fuel injection quantity.

If the boost pressure is too low (below the set limit), it is likely that no vacuum will reach the vacuum chamber of the turbocharger's wastegate actuator, which controls the turbine vanes. In such cases, the most common cause is not the boost control valve itself, but rather cracked or damaged vacuum hoses or angled connectors.
If the boost pressure is too high (exceeding the regulatory limit), the most common cause is usually a sticking or jammed variable geometry nozzle actuator of the turbocharger.

Solution:
Check the entire vacuum hose system for leaks using a manual vacuum pump. Replace any elbows if necessary. If the vacuum hoses are in good condition, check the turbocharger's impeller adjustment.
Disconnect the vacuum hose from the vacuum actuator on the turbocharger and connect the hand vacuum pump to the vacuum actuator. The linkage for the guide vane adjustment must move freely without sticking. If it doesn't, the turbocharger needs to be removed and the test repeated on the detached part.
If the adjustment mechanism is jammed or sticking, the exhaust manifold with its compensator must be removed and carefully inspected. There is a possibility that the exhaust manifold and compensator are corroded internally. Rust particles can detach and enter the turbine wheel of the turbocharger along with the exhaust flow. As a result, the adjustment mechanism of the guide vanes is damaged.

To prevent repeat damage, replace the turbocharger and exhaust manifold components.



Performance deficiency level III

Lack of power, loud knocking noise after cold start or under partial load, engine running unevenly, automatic transmission in emergency mode.

Cause:
Tensioner roller for the camshaft timing belt is difficult to turn, seized, or the tensioning element is defective. Over time, this prevents the timing belt from being properly tensioned. This can lead to deviations in valve timing. In extreme cases, error code 0550 (injection start, control difference) may appear in the engine control unit's fault memory as a result of this issue. In vehicles with automatic transmissions, the transmission control unit will then enter limp-home mode.

Solution:
Remove the timing belt tensioner and check its smooth operation on the mounting bolt; replace if necessary.
Note: The clamping element is oil-damped, can only be compressed slowly and with even force, and must automatically retract. A washer must be installed between the cylinder block and the clamping roller.



Performance deficiency level IV

Gradual loss of power over time, stuttering, and rough engine running.

Cause:
Possible severe wear on the camshaft with deep scoring marks on the valve lobes in the millimeter range, starting around 150,000 km, due to the combination of unfavorable tolerances. Uneven engine running and jerking caused by altered valve opening angles.

Solution:
In the event of a complaint or issue, install specially hardened camshafts. If the cylinder heads, rocker arms, and hydraulic lifters are in good condition, their replacement is not necessary when using the hardened camshafts.

KD camshaft part number:
Intake valve cylinder 4-6 left ......... 059-109-021 P
Intake valve for cylinders 1-3, right side: 059-109-021 Q.
Omit cylinders 4-6 left side... 059-109-022 P
Omit cylinders 1-3 on the right side.. part number: 059-109-022 Q.

According to previous analyses, material loss on the valve lobes of up to 0.5 mm is not critical. Only when wear exceeds 0.5 mm is it justified to replace the camshaft.



Oil level too high

Oil level too high, for vehicles with a vertically mounted oil filter.

Cause:
After the engine has been idle for a longer period, an increased oil level may be visible on the dipstick. This is because the oil has the opportunity to flow back from the oil filter housing into the oil pan.
If the oil level is checked within a maximum of 10 minutes after the engine has been turned off and is still warm, the oil level will correspond to the marking "A" on the dipstick, as described in the owner's manual.

In extreme cases, a prolonged standstill can cause the oil filter housing to become completely empty, which leads to an increase in the oil level in the oil pan.
This process is perfectly normal and does not affect the engine's performance, as the oil filter housing is completely filled with oil just 2 seconds after restarting the engine, which restores the oil level in the oil pan to its normal level.
While the engine is running, the oil filter housing is constantly filled.



Oil leaks on the cylinder head cover

Cause:
1) Insufficient sealant application on the outer bearing covers.
2) Due to unfavorable tolerances, insufficient contact pressure of the valve cover gasket may occur in the area of the joints.

Solution:
"Based on experience, oil leaks are typically caused by the camshaft bearing cover seals rather than the valve cover gasket. Due to the significant assembly effort involved, the front bearing covers should only be removed if there is a leak in the front area of the valve cover. A reliable seal cannot be achieved without disassembly. The contact surfaces between the bearing cover and the cylinder head must be free of oil and sealant residue. Only apply sealant No. 454 300 A2 (blue) to the areas indicated by the hatching on the bearing covers."
"Use a two-part valve cover gasket with a separate crescent shape. Install the valve cover immediately afterward (no more than 2 minutes later). After reaching operating temperature, tighten the mounting nuts of the valve covers to 10 Nm. Ensure that the sealing rings for the injectors (non-replaceable) are not damaged."




Hoher Ölverbrauch. Blue smoke.

Cause:
Faulty check valve in the oil filter module. This prevents engine oil from flowing back into the oil pan, causing it to be burned off through the intake manifold.

Solution:
Check the intake manifold for oil residue. If there is oil residue in the intake manifold and it is not due to a faulty turbocharger, replace the oil filter module.



Oil leak at the cylinder block

Cause:
The bearing covers for the crankshaft bearings are fixed to the outside of the engine block with screws (see image). In some isolated cases, the thread in one of the bearing covers may not be deep enough. The tightening torque of the screw is reached before the screw head makes contact with the engine block and can seal. Over time, this results in oil leakage. Because the area is very difficult to see, there is a possibility of mistaking it for a leak in the oil pan.

Solution:
"Only remove the affected screw and replace it with a shortened one. Alternatively, the existing screw can be shortened by approximately 1.5 mm using a file. Tighten the screw to 25 Nm. No additional sealant is required."



Stuttering under load

Driving behavior issues, including jerking or hesitation under load at engine speeds between 1200-1800 RPM in the higher gears.

Cause:
Faulty or clogged fuel injectors can cause severe engine misfires under load within the specified RPM range.

Solution:
If complaints arise regarding vibrations within the specified speed range, the problem is not always related to the powertrain or transmission. In such cases, check the measurement data blocks 13 and 14 (idle stabilization) while the vehicle is idling. With the automatic transmission, engage gear "D" and activate as many consumers as possible to increase the load on the engine. If one or more fuel injectors deviate significantly from the others or exceed the threshold of 1.5 mg/stroke, you can assume that these injector(s) are defective.

In this case, only replace the faulty injector(s).



Loss of power during acceleration

When accelerating fully, the engine power is abruptly reduced. Error code 00575 (boost pressure) is stored in the engine control unit's fault memory.

Cause:
When demanding full acceleration, the boost pressure may temporarily exceed the target value (for one to two seconds). Before the boost control valve can regulate the pressure, the engine control unit detects a boost pressure that is too high due to the engine protection function and reduces the fuel injection quantity. At the same time, the error code 00575 (boost pressure exceeds regulation limit) is stored. After turning the ignition off and on, the protective function is deactivated, but the error entry remains.

Solution:
In case of a complaint, use an engine control unit with modified turbocharger pressure detection.



Timing belt skipped

Lack of engine power due to a skipped timing belt. In the worst case, this can lead to engine damage.

Solution:
Foreign objects between the gear and the timing belt are often the cause. These objects are usually small animals like mice, which prefer to use narrow cavities, especially in parked vehicles, as storage areas and shelters. A popular spot is underneath the timing belt cover. The stored food or even the animals themselves can get caught in the timing mechanism when the engine is started.

Solution:
As a preventative measure or to avoid recurrence, additional sealing elements can be installed on the timing cover.
No. 059 103 931.
No. 059 103 931 A
No. 059 103 931 C



Timing belt slipping

Timing belt misaligned, significant wear on the leading edge.

Cause:
The idler pulley for the camshaft timing belt is not aligned correctly. There is a manufacturing defect in the housing for the idler pulley on the front sealing flange of the engine block.

Solution:
Replace the timing belt and sealing flange completely, including the tensioner pulley. As part of the necessary work to replace the timing belt, the tensioner pulley should not only be checked for proper function but also for smooth operation on its mounting bolt.



V-belt ineffective or broken

Serpentine belt tensioner, ineffective, broken.
V-belt broken.

Cause:
Due to strong dynamic movements of the ribbed V-belt, it is possible, in the worst case scenario, for noises to occur and subsequently lead to damage or failure of the ribbed V-belt tensioner.

Solution:
Replace the serpentine belt and tensioner.
Make sure to replace the fixed pulley on the generator with a freewheeling pulley.
Idler pulley for Bosch alternator No. 028 903 119 T.
Valeo generator, part number 028 903 119 AC.
Make sure to install a spacer ring (part number 028 903 237 A) between the freewheel pulley and the generator.



Lack of power, rough idling, black smoke

Problem description.
Lack of power, black smoke, soft jerking during acceleration, engine stalling.
Top speed not reached, starting problems.
Error codes 00575, 00553, or 17656 found in the error memory.

Cause.
1. Various process uncertainties.
2. Air mass meters during specific production periods.
3. Turbocharger (also present in 81 kW engines, and may be the cause of occasional power loss).
4. Low-quality rapeseed methyl ester fuel. Air in the fuel system.

Solution:
Vehicle inspection for:
• Added exhaust system and catalytic converter.
• Blocked raw air intake (before the air filter or intake screen).
• Torn, split, or improperly fastened charge air ducts.
• Exhaust gas recirculation (EGR) and turbocharger control lines that are disconnected, incorrectly connected, torn, or broken.
• Electromagnetic control valve for turbocharger pressure regulation (only in cases of engine misfire complaints).
• Turbocharger (only in cases of complaints regarding performance or excessive black smoke).
• In Passat 4 TDI vehicles manufactured from May 1995 onwards, which use spring band clamps for mounting the intercooler pressure pipes, there have been instances of the intercooler pressure pipes slipping between the turbocharger and the intercooler. The cause is a spring band clamp on the pressure connection of the turbocharger. Since the turbocharger's pressure connection was not designed to accommodate spring band clamps, a hose clamp must continue to be used in this location.
• For Passat 4 vehicles with spring band clamps used to mount the intercooler charge air ducts, the spring band clamp must be removed from the turbocharger pressure port (the connection where air is directed to the intercooler) and replaced with a hose clamp, part number N 024 507.4.
• Remove all lubricant from the connections for the charge air ducts and hose sections in the charge air system.

2. Read the error codes.
If the error combination 00575 and 00553 is stored in the fault memory, the mass airflow sensor should not be replaced because error 00553 is only a secondary error.
Troubleshooting this case, such as entry number 00575.

If error code 00553 - "Mass airflow sensor: Implausible signal" appears, replace the mass airflow sensor.
Under no circumstances should the mass airflow sensor be replaced if the errors are occurring sporadically!
Check the mass airflow at full load. Inspect the air filter element for damage.
If no error code is displayed in the diagnostic memory and no other faults are found according to the repair manual, replace the mass airflow sensor if the manufacturing date is before calendar week 16 of 1994.
If repeated failures occur, definitely replace the air filter cartridge, as these cases are often due to contamination.

3. If no errors are found after steps 1 and 2, replace the turbocharger.
After a turbocharger failure, inspect the intercooler piping for leaks. A leak can be the cause of turbocharger damage.
4. If error code 17656 is stored in the fault memory, there is a possibility that the fuel filter is clogged. This may have been caused by the use of unsuitable rapeseed methyl ester fuel. A clogged or blocked fuel filter can lead to high pressures in the fuel supply line.

To determine the vacuum pressure, perform the following measurement:
A T-piece (e.g., part number 251 201 346) must be installed in the fuel supply line at the filter. To do this, disconnect the supply line from the fuel filter and connect it to the T-piece. Reconnect the other free end of the T-piece to the fuel filter using a hose piece. The third outlet on the T-piece must be connected to a pressure gauge. The line between the T-piece and the pressure gauge should not be too short, so that no fuel can reach the pressure gauge. The vacuum pressure must be measured at idle speed and at 2,000 rpm. If the vacuum pressure is above -350 mbar, the fuel filter must be replaced.
With the new filter installed, the measurement should be repeated to rule out other components (for example, kinked fuel lines).
Do not perform extensive troubleshooting on the fuel injection control unit or diesel injection pump before ruling out a clogged filter.


It is also possible that air has entered the fuel system.
After 2 minutes of the engine running at idle, the bubble length is 2 cm or more at the highest point of the transparent fuel supply line from the fuel filter to the injection pump (for black lines, install the transparent line directly from the filter into the supply line leading to the injection pump - minimum length 10 cm; use and modify part number 1J0 130 307 B).
Possible causes of air bubbles include: leaks or fuel vapor bubbles caused by contamination with gasoline.


Debugging:
Install a transparent fuel hose (see above) into the fuel line from the tank to the filter, directly in front of the fuel filter (ensure the clamps are tight!). Let the engine run at idle for 2 minutes to bleed any air from the fuel line leading from the tank to the filter. Turn off the engine for 1 minute and compare the size of the bubbles in the hose before the filter and after the filter, leading to the injection pump.

• The clear hose before the fuel filter is bubble-free or has bubbles no larger than 5 mm.
The cause is related to the fuel filter/pre-heater valve.
Possible causes include:
Leaks (these are air bubbles).
The filter becomes clogged over time with particulate matter, leading to a significant increase in flow resistance (due to fuel vapor bubbles, specifically gasoline vapors). This occurs whenever small amounts of gasoline are present in the diesel fuel.
Measure:
- Replace the filter with a preheating valve.
- Replace potentially contaminated fuel.
• Approximately equally sized bubbles are visible in the transparent tubing both before and after the fuel filter (2 cm or larger).
The cause is likely in the fuel system, specifically the fuel level sensor or the line leading to the filter. In this case, install a transparent hose directly at the outlet of the fuel level sensor, connecting it to the supply line.
If the air bubble is not completely gone after approximately 30 seconds of engine idle, or if the size of the air bubble is greater than 5 mm after approximately 15 seconds of engine standstill, then the tank unit is defective.

Measure:
- Replace the charging unit.
- Otherwise, identify and eliminate the leak between the fuel tank unit and the fuel filter.



The engine won't start.

The engine has no compression.
When starting, the engine sounds like it's revving without any load.

Cause.
Due to a casting defect, the control mechanism for the intake manifold flap is jammed.

Solution:
In case of malfunction, replace the component.



Engine does not start II

Engine won't start.
The error sometimes occurs sporadically.

Cause:
Power supply relay for the motor control unit is defective.

Solution:
Testing the voltage supply of the engine control unit (ECU).
In case of a defect, replace the relay.



Lack of power with noises

Sudden noises accompanied by power loss.

Cause:
Due to irregularities in the valve manufacturing process, damage to the valve disc may occur in isolated cases.

Solution:
Part exchange.



Pulsating sounds, croaking noises

Pulsating noise coming from the front of the car on the right side, occurring at approximately 1,400 to 1,800 RPM and during slight acceleration.

Cause:
The noises are caused by pulsations in the vacuum line between the solenoid valve and the exhaust gas recirculation (EGR) valve. The diaphragm of the EGR valve vibrates at the same frequency as the vacuum pulsation.

Solution.
Bring the vehicle to its operating temperature. Disconnect the connector from the solenoid valve and perform a test drive. If the noise no longer occurs, please replace the solenoid valve and clear the error codes in the engine control unit.



Idle speed control

Group 13 (in the engine control unit):

Field 1: Injection quantity difference between cylinder 3 and cylinder 2.
Field 2: Injection quantity difference between cylinder 1 and cylinder 2.
Field 3 and Field 4: no setpoint value.


Group 14:

Field 1: No setpoint value.
Field 2: Injection quantity difference between cylinder 6 and cylinder 2.
Field 3: Injection quantity difference between cylinder 4 and cylinder 2.
Field 4: Injection quantity difference between cylinder 5 and cylinder 2.

Set Point: -2 mg/H .. +2 mg/H

Positive value:
Each cylinder has a lower power output than the reference cylinder and is therefore supplied with more fuel.

Negative value:
Each cylinder is more powerful than the comparable cylinder and therefore receives less fuel.