Audi A4 AFN '97 won't start -> Is the engine control unit (ECU) faulty?

Hello,

I'm only here because I drive an Opel (diesel), and I have absolutely no knowledge of VW/Audi.
The following problem:
My uncle's Audi A4 (TDI 81kW / AFN engine, year 1997) won't start anymore. It started with difficulty starting the engine.
He was still able to drive it there, but it's gotten worse since then, and now it won't start at all.
Workshop #1 (a contact of my uncle's) is unable to establish a connection with the control unit.
Workshop #2 (Audi authorized service center): Unable to establish a connection with the control unit (their diagnosis: faulty control unit). Additionally, they found a defective pre-lift pump.
According to them, the car should still run even with a faulty fuel pump, and fuel is also reaching the ESP system at the front.
Since I work with electronics professionally (but not in the automotive field), I should now take a look at the control unit.

However, I still want to find out more information here first.
-Are there any typical problems or diseases associated with this model (e.g., ESP issues, variable valve timing malfunctions, broken cables, porous return lines, cold solder joints, corroded contacts)?
Can error codes be cleared without a diagnostic plug?
-läuft der tatsächlich mit def. Voil booster pump?
-If different speed sensors were installed (if I need to consult with an expert from xbay), do the speed sensors need to be programmed to the car, or is it simply a matter of connecting them and they will work?
-Does anyone have any other ideas?

Today I will be disassembling the power supply unit (PSU) to check for corrosion, cold solder joints, and defective components. I won't be able to perform a system test under load.
I somehow have the feeling that the error might be outside of the SG (System Group).


Andi.

Rekord81 wrote:

Workshop #1 (a friend of my uncle's) is unable to establish a connection with the control unit. Workshop #2 (Audi authorized service center): Unable to establish a connection with the control unit (their diagnosis: faulty control unit). Additionally, they found a defective pre-lift pump. According to their statement, the car should still run even with a defective pre-injection pump, and fuel is also reaching the ESP at the front.

I only know about electric pre-injection pumps on VAG diesel engines for PD engines (not: AFN). This is not to be confused with the rotary vane pump in the VP37.
"No connection" can also originate from the infamous relay 109, which is the main power supply for the engine electronics. If the preheating light doesn't even flicker briefly when you turn the ignition ON, that's a strong indication of a problem.

Quote:

Are there any typical diseases associated with this model (ESP, variable valve timing issues, broken cables, porous return lines, cold solder joints, corroded contacts...)?

Occasionally, the timing chain gears loosen on the crankshaft.
Porous leak lines are also common, and when the organ is playing, many air bubbles pass through the transparent supply line.

Quote:

-kann man Fehlercodes ohne Diagnosestecker ausblinken ?

No.

Quote:

-Does it actually run with a defective pre-pump?

See above.

Quote:

Since different ECUs were installed (if I need to mention xbay), the ECUs must be programmed to the car.

Yes, because of the WFS. If this is not done, the engine (which is otherwise fine!) will start, run normally for about 1 second at idle, and then shut off again.

While a faulty MSG (Main System Generator) is not impossible, it's an extremely rare occurrence within this forum.

Is a third-party radio installed? This might be blocking the diagnosis. Try disconnecting it and trying again.

The diagnostic signal path runs from the WFS (Vehicle Communication System) to the MSG (Modular Service Interface). Is it still possible to communicate with the WFS? Depending on the findings, the wiring between the diagnostic connector and the WFS, or between the WFS and the MSG, should be measured and checked for short circuits.

Does the engine control unit (ECU) receive any power? Either measure the voltage or check if the preheating indicator light comes on.

The most common problem with VP engine starting is air in the fuel line. Check if the A4 also has a clear fuel line and watch for air bubbles during startup. Other frequent causes include a weak battery or starter motor, incorrect valve timing, and, to a lesser extent, a faulty ESP (Electronic Stability Program). We have an article here that discusses these starting problems; please take a look.

Error codes in vehicles from the Volkswagen Group (VAG) can generally no longer be displayed via blinking LEDs, depending on the platform, starting roughly from the early 1990s.

I'm not familiar with a pre-lift pump on the AFN engine, although I haven't had one in an Audi yet either. However, the VP37 remains a self-priming pump. If there is indeed a pump in the tank, its function is the same as on the V6 engines: to pump diesel from the lowest point of the tank into the reservoir within the tank when the tank is empty, from which the engine then draws fuel. Unless the tank is almost empty, the pump is not needed.
Several control units are compatible with the AFN engine. There are essentially two key distinguishing features: A) With or without WFS (Wastegate Flap System), and B) For VW or Audi (the brake/clutch pedal is connected to either ground or positive voltage). Check the Bosch Ecat catalog; you'll find which control units are compatible and which have been replaced by newer generations.

Regards,
Sure.

EDIT: Okay, I must have fallen asleep on the keyboard, and as usual, Ulf was faster.

Das geht ja flott hier. Thank you very much.

Relay 109 sounds interesting, where is that relay located?
What does the glow plug indicator light look like in an Audi? Does it always illuminate briefly?
If the WFS were defective (I've also considered that possibility), the motor would still have to run for at least one second. That would rule it out, because the motor isn't running at all.

"The timing belt was replaced some time ago. If the valve timing had been misaligned since then, it should have caused noticeable problems while driving. I need to investigate this further."
"If the valve timing or ignition timing is incorrect, does white smoke come out of the exhaust? Or could it be due to insufficient fuel injection or a low starter speed? I haven't seen any smoke at the rear, nor have I smelled any diesel fumes."

The pre-lift pump only comes into play when the fuel level is low? Perhaps it has already sucked in air prematurely from the back at some point?

Rekord81 wrote:

Relais 109 hört sich interessant an, wo sitzt das Relais denn ?

Take a look at the fuse box . It might have a different number (use the search function, or first check if the indicator light comes on).

Rekord81 wrote:

What does the glow plug indicator light look like in an Audi (the filament)? Does it always illuminate briefly?

Just take a look at the instrument cluster (speedometer). You should be able to see something that looks like that there.

Rekord81 wrote:

Falls die WFS defekt wäre (daran hab ich auch schon gedacht), müsste der Motor immer noch 1 sek lang laufen ?

Yes, the motor would still run for one second, and then the control unit (MSG) would stop the motor again.

Rekord81 wrote:

Vor einiger Zeit wurde der Zahnriemen gemacht, wenn sich danach NW-Steuerzeiten verstellt hätten, müsste der auch event. beim Fahren immer schlechter gelaufen sein.

Adjusted valve timing often becomes noticeable primarily in the starting behavior of the engine, especially for drivers who are not paying close attention.

Rekord81 wrote:

Vorförderpumpe kommt also erst ins Spiel, wenn der Tanklevel niedrig wird ?

If it even has one. We've also had cases here where a workshop claimed it was defective, even though none was installed .

What about radio and air?

Regards,
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It refers to a sudden and strong gust of wind.

The car is currently parked outside at workshop #1. Since we're having terrible weather here, I'm waiting until it gets a bit better. I'll decide what to do next by tomorrow morning at the latest.
By the way, the workshop #2 wanted to replace the MSG unit (for €1300) and the pre-injection pump (for €700). That's on hold for now until I at least take a look at the control unit.

Thank you very much for the answers!

Andi.

[Translating...]

Zum Test kannst du das MSG an jedem TDI mit 90 oder 110 PS mindestens aus den Baujahren 94-97 testen. Der Motor muß zumindest für 1 Sekunde laufen.

Wenn du VAG-COM zur Verfügung hast (Shareware + Adapter reicht) oder den Bosch Tester der Werkstatt und das MSG auf dem Schreibtisch auslesen möchtest:

Rudi in https://community.dieselschrauber.org/en/viewtopic.php?t=15170&highlight=schreibtisch wrote:

Wenn du die Möglichkeit hast, bau dir einen Adapter, mit dem du die Motorsteuergeräte direkt auf dem Schreibtisch betreiben kannst. STG: Pin 1 Masse Pin 23 12V Pin 61 K-Line Diag: Pin 4,5 Masse Pin 16 12V Pin 7 K-Line K-Line wird direkt verbunden, 12V und Masse müssen an beide Stecker und eine Einspeisemöglichkeit für ein Netzteil haben (12V / 1A reicht; die MSA15 zieht auf den Schreibtisch knapp 300mA, wenn sie erstmal läuft).

Gruß
Guste

Okay, so...
The control unit is open, all solder joints and components look perfect visually, and all capacitors are okay. I expected that.
"New radio not installed, fuel line is opaque, ESP receives diesel."
According to the mechanic, the pre-lift pump located at the rear of the tank is drawing 17 amps or more and blowing the fuse. Apparently, the pump is needed for full load operation, as I understand it.

Was mir vorher in der Werkstatt aufgefallen ist, wir haben an Pin 1 und 23 = 0V gemessen (allerdings mit so einem komischen LED-Werkstattprüfer) ich werd das nochmal mit dem eigenen Messgerät prüfen. Relais 109 hab ich noch nicht lokalisiert, ist das im Motorraum bei den dicken Sicherungen (neben dem MSG), oder ist das im Innenraum bei den Sicherungen ? Also Relais 109 versorgt das MSG, aber woher wird Rel 109 angesteuert ? ÜRegarding the ignition switch contact?

What does... actually mean?

Quote:

Diag: Pin 4 and 5: Ground. Pin 16: 12V. Pin 7 K-Line

Is the diagnostic tool being powered? Should I measure ground (GND) at pin 4 and 5, and 12V at pin 16 on the connector in the vehicle (with the control unit disconnected)?
Is the K-line from the MSG connector directly electrically connected to the diagnostic port? If so, I can reasonably check for continuity there.

"I don't have a VAG-COM device, but I do have an oscilloscope. Can I use a simple voltage signal to stimulate the MSG (Motor Steuergerät - Engine Control Unit) and measure a confirmation telegram?"

"I'm asking some of these questions in advance. First, I need to verify whether pin 23 is actually not receiving voltage, or if that was a measurement error. By the way, none of the glow plugs illuminated when the ignition was turned on, but the light directly next to it (presumably for auto start/key=WFS?) lit up for 2 seconds and then went off (which is normal behavior in the cars I'm familiar with, or part of the standard light check)."
Are the two K-lines on MSG pin 7 and pin 61 electrically connected in parallel, or are they two separate K-line channels?

Almost forgot: the MSG is a Bosch part, according to the sticker. Can the local Bosch service center test it for functionality, or are they unable to do anything with it?
Andi.

Hello,
"I looked at the car again tonight, trying to find out if the control unit receives power on pin 23. I found copies of circuit diagram excerpts in the car from workshop #2 (an Audi repair shop). I think I've now located the relay that supplies voltage to the MSG (Main System Gateway). According to the circuit diagram, it's labeled J322 (relay socket number 3) and provides 12V to pins 23, 68, and 45 of the MSG."
Jetzt kommt was seltsames: Das Relais wird über eine Leitung aus dem MSG (Pin 42) angesteuert, dh. solange das MSG nicht gesteckt ist, kann das Relais nicht anziehen und ich kann dann keine 12 V an der autoseitigen Buchsenleiste an Pin 23 (also Buchse 23) messen. Wenn ich den Anschluss 42 im MSG verfolge, endet die Leitung an einem nicht bestückten SMD Bauelement. Also der liegt quasi in der Luft. I don't understand it.

Does anyone have a picture of an open AFN-MSG so I can see if the corresponding component is installed?

Andi.

On the A4 model, it has a different part number. I also looked for it on my car.

It is located in the water tank housing and can be found in the compartment with the engine control unit; its part number is 219.

Rekord81 wrote:

Jetzt kommt was seltsames: Das Relais wird über eine Leitung aus dem MSG (Pin 42) angesteuert, dh. solange das MSG nicht gesteckt ist, kann das Relais nicht anziehen und ich kann dann keine 12 V an der autoseitigen Buchsenleiste an Pin 23 (also Buchse 23) messen. Wenn ich den Anschluss 42 im MSG verfolge, endet die Leitung an einem nicht bestückten SMD Bauelement. Also der liegt quasi in der Luft. I don't understand it.

You probably followed something incorrectly there.
Here's how the main relay is activated:

At 3:00 PM, a signal also goes to the MSG (pin 38?) and activates the switching stage for the main relay there (output = pin 42, which is connected to ground). This energizes the circuit and supplies power to the entire motor electronics.

Not entirely wrong, but incomplete.
Pin 42 has a hidden connection to an SO20 SMD component. It might be a relay driver IC. The other terminal of the unpopulated SMD is directly connected to GND, meaning that if I bridge it, the relay should activate (and likely drain the battery within a maximum of 3-4 weeks).
Okay, here's what I'm going to do: Tomorrow, I'll reassemble the MSG and measure at the relay socket to see if the relay is being activated when the ignition is turned on. If it's not, I'll temporarily solder a 200mA polyfuse onto the unused SMD pad. This should then activate the relay. If that's the problem (meaning the relay driver might be faulty), I can build my own KL15-controlled driver circuit.
If the relay is being correctly activated, I have to assume that the MSG (presumably a module or component) is receiving power and is therefore defective. Unless, of course, the relay itself is faulty, but that was replaced by workshop #2 yesterday.

Does the K-line only become active when the MSG is powered by voltage via the relay (i.e., pin 23), or should it already function if there is only voltage at KL 15? Does the relay control only work with a running MSG processor?

I'm asking in advance: Does anyone know what type of voltage regulators are installed in the MSG? I won't be able to see them until I remove the heat sinks.


Andi.

[Translating...]

guste100 wrote:

Rudi in https://community.dieselschrauber.org/en/viewtopic.php?t=15170&highlight=schreibtisch wrote: Wenn du die Möglichkeit hast, bau dir einen Adapter, mit dem du die Motorsteuergeräte direkt auf dem Schreibtisch betreiben kannst. STG: Pin 1 Masse Pin 23 12V Pin 61 K-Line Diag: Pin 4,5 Masse Pin 16 12V Pin 7 K-Line K-Line wird direkt verbunden, 12V und Masse müssen an beide Stecker und eine Einspeisemöglichkeit für ein Netzteil haben (12V / 1A reicht; die MSA15 zieht auf den Schreibtisch knapp 300mA, wenn sie erstmal läuft).

nun dem nach an Pin 23

Rekord81 wrote:

1) Is the K-line from the MSG connector directly electrically connected to the diagnostic connector? Can I stimulate the Message Signal Generator (MSG) with a simple level to generate a receipt telegram that I can measure? 3) By the way, none of the preheating lights illuminated when starting the engine, but the light directly next to it (car + key = WFS?) turned on for 2 seconds and then off (which is normal for the cars I know, or rather, a normal light check). 4) Are the two K-lines connected to MSG pin 7 and pin 61 electrically in parallel, or are they two separate K-line channels? 5) Almost forgotten: the MSG is a Bosch part, according to the sticker. Can the local Bosch service center test it for functionality, or are they unable to do anything with it?

Please provide the German text you would like me to translate into English. I will then give you only the translation, without any explanations.

guste100 wrote:

Die Diagnoseleitung läuft über die WFS zum MSG. Läßt sich mit der WFS noch kommunizieren? Je nach Befund Verkabelung zwischen Diagnosebuchse und WFS oder eben zwischen WFS und MSG ausmessen und auf Kurzschlüsse prüfen.

2) When the supply voltages are switched on (according to the wiring diagram above), the MSG communicates with the immobilizer via the K-Line. You can check the function using a simple LED (of course, with a current-limiting resistor ).
3) Then that might also be your mistake. Locate the relay and check its functionality. The relay is a very common cause of errors . And if the relay doesn't engage, the MSG (Modular Sensor Group) cannot be reached via diagnostics either.
"Unfortunately, I don't have a wiring diagram available right now, but I wasn't aware that the MSG has two K-lines. However, I can only be certain about this with a circuit diagram."
5) I highly doubt that the standard Bosch service can test these things, but it's possible they might have another 90 or 110PS TDI engine on hand that they could use for testing. But I'll say it again: In over 99% of cases, the MSG is _NOT_ your source of error . So put the MSG back together and check the surrounding components first!

However, the relay itself cannot be the sole cause, because if that were the case, the starting problem would have worsened more gradually. Nevertheless, it's important to check first whether the MSG (Main System Generator) is also receiving power on pin 23.

What is connected to the fuse for the alleged pre-charging pump? For testing purposes, I would disconnect the pump and replace the fuse with a working one. In the worst case, voltage might be supplied to relays or other components (this is just an example, I don't have a SLP available).

guste100 wrote:

.Unfortunately, I don't have a wiring diagram available right now, but I'm not aware that the MSG has two K-lines. However, I can only be certain about that with a circuit diagram.

Shouldn't one of the two wires rather be the (archaic) L-line?

Hello.
I think that's probably it with the MSG. Yesterday, I measured the voltages (at the tantalum capacitors) on the open MSG in the car. Everywhere, I got a stable 5V. The preheating indicator light is NOT illuminated, nor is the oil warning light.
Zuhause auf dem Labortisch kann ich keine Aktivität an der K-Line erkennen. Ich kann überall (an allen Steckeranschlüssen und da, wo ich auf der Platine sonst noch an mehr oder weniger zufälligen Stellen gemessen habe) nur statische Spannungen messen. Kein PWM oder sonstwas. Nur die beiden Quarzoszillatoren schwingen. Das MSG zieht nach Anlegen der Spannung 320 mA, geht nach 1 Sek kurz auf 330 mA und kommt kurz danach dauerhaft auf ca 312 mA. It's possible that some kind of initialization process occurs after the power-up sequence.

I'm now assuming that the MSG is likely defective, and I lack the equipment (and especially the MSG wiring diagram) to conduct further investigations.

If I purchase a used Message Center (MSG), does it need to be reset in the donor vehicle?
Does a code number need to be included with used MSGs (Motor Sequence Generators) for unlocking or pairing?

Andi.