Defective Pressure Sensor: STG Diagnostics

Hello,


I read out my Caddy (AHU) using VAG-COM.

Problem: The engine goes into limp mode after a short time, especially in 4th and 5th gear, but also when accelerating in the lower gears. (See also the post about the VTG - Valve Timing Gear - module).
After restarting, the game starts from the beginning.

Following the instructions for 'Troubleshooting with VGA-Com,' I observed a significant deviation in group 10, which I am reporting.

With the engine idling!

Barometric Pressure: 969.0 mbar

Manifold Pressure: 1417.6 mbar


Here's another log attached.

Thursday, July 1, 2004, 5:42:54 PM
028 906 021 DL, 1.9L R4 EDC, G00SG, 0828.

Group A: '010',,,,Group B: Not Running,,,,Group C: Not Running
'Mass Air Flow, Barometric, Manifold, Position,...'
,TIME,,Pressure,Pressure,Throttle,TIME,,,,,TIME,,,,
Marker, STAMP, mg/R, mbar, mbar, %, STAMP, , , , STAMP, , ,
,0.38,365.8,969.0,1417.8,0.0,,,,,,,,,,
,0.78,369.1,969.0,1417.8,0.0,,,,,,,,,,
1.19, 365.8, 969.0, 1417.8, 0.0, , , , , , , , , , ,
1.59, 349.1, 969.0, 1417.8, 17.3, , , , , , , , , , ,
1.99, 372.4, 969.0, 1417.8, 22.4, , , , , , , , , , ,
2.42, 382.4, 969.0, 1417.8, 21.2, , , , , , , , , , ,
2.83, 405.6, 969.0, 1428.0, 32.5, , , , , , , , , , ,
3.23, 432.3, 969.0, 1458.6, 31.8, , , , , , , , , , ,
3.64, 438.9, 969.0, 1468.8, 34.5, , , , , , , , , , ,
4.07, 415.6, 969.0, 1468.8, 36.5, , , , , , , , , , ,
4.46, 415.6, 969.0, 1468.8, 40.8, , , , , , , , , , ,
4.87, 405.6, 969.0, 1468.8, 46.7, , , , , , , , , , ,
5.27, 432.3, 969.0, 1468.8, 50.2, , , , , , , , , , ,
5.66, 485.4, 969.0, 1519.8, 58.0, , , , , , , , , , ,
6.09, 522.0, 969.0, 1591.2, 61.6, , , , , , , , , , , ,
6.52, 578.5, 969.0, 1723.8, 64.7, , , , , , , , , , ,
6.93, 658.4, 969.0, 1948.2, 64.7, , , , , , , , , , ,
7.34, 714.9, 969.0, 2182.8, 64.7, , , , , , , , , , ,
7.75, 625.1, 969.0, 2131.8, 62.0, , , , , , , , , , ,
8.16, 495.4, 969.0, 1876.8, 0.0, , , , , , , , , , ,
8.58, 512.0, 969.0, 1683.0, 28.6, , , , , , , , , , ,
8.99, 658.4, 969.0, 1764.6, 73.7, , , , , , , , , , ,
9.38, 688.3, 969.0, 1968.6, 73.7, , , , , , , , , , ,
9.79, 731.5, 969.0, 2111.4, 76.5, , , , , , , , , , ,
10.19, 704.9, 969.0, 2162.4, 78.0, , , , , , , , , , ,
,10.61,691.6,969.0,2131.8,78.4,,,,,,,,,,
11.04,668.3,969.0,2111.4,83.9,,,,,,,,,,
11.46, 655.0, 969.0, 2080.8, 84.3, , , , , , , , , , ,
,11.87,645.0,969.0,2070.6,84.3,,,,,,,,,,
12.30,631.8,969.0,2050.2,84.3,,,,,,,,,,
12.72, 605.1, 969.0, 2009.4, 84.3, , , , , , , , , , ,
,13.13,588.5,969.0,1958.4,0.0,,,,,,,,,,
13.53, 505.4, 969.0, 1734.0, 0.0, , , , , , , , , , ,
13.93, 575.2, 969.0, 1693.2, 67.8, , , , , , , , , , ,
14.33, 701.6, 969.0, 1989.0, 80.0, , , , , , , , , , ,

Regarding the pressure gauge I connected to the pressure line of the control unit (STG), I'm getting a reading of 0 bar at 900-1400 RPM. After that, the pressure builds up to 0.8 bar.

I disconnected the pressure line to the control unit (STG) and, using a hand pump with a pressure gauge, pressurized the control unit to 0.35 bar. My Caddy is now running and has power, and it no longer goes into limp mode.

Question:

• Is the pressure sensor in the control unit defective?
• Can it be repaired by the user? (Where can you find the spare parts?)

Thank you very much for your help in advance.


Regards,
Bernd[/u]

TT - Diesel wrote:

With group 10, I have a significant deviation, the pressure. With the engine idling! Barometric Pressure: 969.0 mbar Manifold Pressure: 1417.6 mbar Attached is another log file.

So, I can't bring myself to read the log -> eye cramps .

But the difference between the ambient pressure and the boost pressure clearly indicates that there is something wrong with the boost pressure sensor.
It might just be a cold solder joint.

hello,

'Please log group 11, not group 10. Group 11 shows the target and actual engine speed, as well as boost pressure. What you're seeing is just the ambient air pressure reading from the control unit, which is 979 mbar, so it's okay (my control unit reads only 670 mbar, so mine is probably faulty) and it's not changing.'

best regards

Otherwise, I would also say that the boost pressure sensor is faulty.

It's quite likely that the pressure sensor is defective. One option is to find a used control unit with the same pressure sensor. Replacing it isn't the problem. Maybe HitzPätz will sell you the corresponding replacement part. They also repair control units, but that usually costs between 400 and 500 €. I'm not sure if they sell replacement parts, though; it's worth trying.

Best regards, Holger.

Hello,

Unfortunately, HitzPätz does not sell ET parts.

I ordered a Motorola MPX 4250 AP from Spoerle.
The MPX 4250 AP has a hose connection, and the values should be...
that are equivalent to the original Bosch parts.

The fact that it has 6 pins isn't a problem, as only the first 3 are used. The other pins can be removed (they are only present due to the design -> standard).
The price is €27 plus VAT, with shipping and cash on delivery costing approximately €40-€45.

As soon as there is any new information, I will provide further details here.

Regards,
Bernd.

TT - Diesel wrote:

As soon as there is something new, I will provide more information here.

Please also consider the possibility that the old sensor might only have a cold solder joint.

Then, although the new sensor would be unnecessary, others might still learn something from your story .

Hello Ulf,

I had already resoldered the pressure sensor, but unfortunately, there was no change.

Original pressure sensors are only supplied by Bosch to authorized repair shops.
Therefore, HitzPätz is not allowed to supply ET (presumably referring to 'Ersatzteile,' or spare parts), and Bosch is very careful to prevent any ET from entering the market.

However, in the meantime, I tried something and found the following solution.
'Das 10 Cent Tuning' inspired me to do it.

I replaced the SMD resistor (10 kOhm, at the signal output of the pressure sensor) with two stranded wires. I then soldered a fixed resistor with 40 kOhm and a potentiometer with 50 kOhm (in series) to those wires.

This allowed me to reduce the boost pressure sensor reading from 1417 mbar to 1030 mbar while the engine was idling.
(Air pressure 969 mbar) This means that, according to VGA-Com, at full boost pressure, the turbocharger produces a pressure of 1887 mbar, which is within the optimal range according to the engine control unit (ECU).

On my pressure gauge, I'm seeing a 'real' boost pressure of 1.00 to 1.05 bar, which shouldn't be a problem for the turbocharger.

If we now implement this '10-cent tuning,' the motor's power output will likely increase significantly, as will the case with other nozzle configurations.

But I will still replace the pressure sensor and re-solder the original resistor back in.

My Caddy has already covered 274,000 km (manufactured in 2000) and is supposed to last until next year.
(estimated to be around 350,000 km)

So far, I have only replaced the servo pump (202,000 km) and the right front wheel bearing (255,000 km), and now I'm having an issue with the STG (Steering Torque Generator).

Regards,
Bernd.

Please also consider this, even if the old sensor only has a cold solder joint.

Hello!

I need to say something about this.

Engine: 1.9 TDI AFN, manufactured in 1998.
I was able to increase the boost pressure using a diode in the sensor signal, following the instructions on dieselschrauber.de. Unfortunately, a strong vibration caused by a bump in the road detached one of the three solder joints on the pressure sensor. Of course, in that condition, the car only ran in limp mode.
The real problem arose when I noticed that reconnecting the positive, negative, and signal wires didn't improve anything. Afterward, the car only ran with half of the intended boost pressure.
Multiplying the voltage drop of the sensor signal to the control unit (ECU) by four (4x) using three additional diodes resulted in only slight improvement. -> 0.7 bar instead of 0.5 bar - TARGET: 0.95 bar.

Okay, here's the translation:

'Now my question: Can the engine control unit (ECU) or the sensor's control circuit be damaged by starting the engine or by operating it with a severed wire (I no longer remember exactly which one) connected to the pressure sensor?'

Thank you, Peter.



EDIT: Solution to 'cold solder joint' found in the thread.
'Boost pressure sensor (internal to the control unit - AFN...)'