Audi Q7: Won't Start - Troubleshooting Guide

Hello, my Audi Q7 4.2 TDI with 326 horsepower, manufactured in August 2009, will not start after a thunderstorm. After a thunderstorm during the night, I was just at home and couldn't get out of the car because of the heavy rain. The car was turned off, and then there was a very loud bang and a lightning strike at the same time. I was very scared and also felt like the car was moving.

The next morning, I wanted to drive away, but the engine wouldn't start. The preheating light is blinking and won't turn off. Error codes were read, including "steering angle sensor incorrectly programmed," "transmission control unit incorrectly programmed," and "engine control unit incorrectly programmed," among others. The car was then towed to a VW dealership. After an initial diagnosis, the high-pressure pump was replaced. There was no rail pressure. Then, the engine control units were sent in for inspection. The control units were found to be in order. Next, the fuel pre-pump was replaced. Sensors and the pressure regulating valve on the rail were replaced, and the fuel injectors were checked by a Bosch service center, and everything was found to be in order.

The car isn't getting any fuel pressure and won't start. Audi is stumped and doesn't know what to do. As it stands now, I'm going to get the car back unrepaired. Maybe someone here can help me.

Hello,

Quote:

Errors were read out

...an automatic scan would be helpful here!

The first spontaneous thought I had while reading this was that the strong electromagnetic field from the lightning strike might have damaged one or more control units.

Was the WFS control unit inspected?

Due to which diagnosis were the high-pressure/pre-charge pump and sensors replaced?
Just because of "no rail pressure"?

Randomly swapping parts, hoping to find the right one, is not effective and, moreover, it's expensive!

Best regards, Richard.

Das war auch meine Vermutung. Aber Audi ist da anderer Meinung. Es war auch ein Gutachter der Versicherung da. Laut ihm kann er kein Blitzeinschlag/Blitzaustritt feststellen. Deshalb können auch keine Steuergeräte Schaden genommen haben. Die Hochdruckpumpe wurde dann gegen eine Austauschpumpe getauscht weil kein Raildruck da war. Vermutung HDP defekt. Ka rail pressure.

Danach die Vorförderpumpe getauscht weil vielleicht die eingebaute zu wenig Druck macht. kein Raildruck. Danach meine HDP zu Boschdienst prüfen lassen. Pumpe ok. Beide Motorsteuergeräte zum prüfen bei Firma ECU. Steuergeräte ok keine Fehler, auch kein Wasserschaden im Steuergerät weil das öfter mal vorkommt. Railrohr ausgebaut und auf Haarrisse überprüft. Railrohok.

"Have all 8 injectors checked at a Bosch service center. 2 injectors were replaced due to leakage. No rail pressure... The previous errors have been cleared, and the car should start, but it doesn't. The immobilizer has been checked and is working correctly. The immobilizer was bypassed, but the car still won't start. No rail pressure. Audi says they can read all the control units, so they can't be defective. However, there must still be an issue with the electronics somehow."

Someone needs to start a guided troubleshooting process here.

It only takes a single signal from a critical sensor during the startup process to cause a problem.

The suspicion that a defect was caused by overvoltage or electromagnetic radiation is very likely. Since two ECUs have already been to the company, I think it might be worthwhile to have the Q7 checked there as well, so that a comprehensive analysis can be carried out. In my opinion, it's worth a try.

BTW: The expert's statement is also very interesting, that no damage could have occurred simply because there are no traces. It seems to be very up-to-date from an electrical engineering perspective .

Thanks for the information. The car is running again. It was actually the control unit. The two weren't communicating with each other. The control unit has been replaced, and the car starts immediately.

Premature celebration... Now, when driving, the preheating light comes on, and the error message indicates "rail pressure too high."

Hello,

The target value and actual value for the rail pressure can be found in the measurement data blocks of the engine control unit.
The rail pressure sensor is directly connected to the control unit. I would inspect the wiring harness for any damage.

Best regards, Rainer.
PS: It would be worse if the rail pressure was too low.

Andyvr666 wrote:

Too early to celebrate... Now, when driving, the preheating light comes on, and the error message indicates "rail pressure too high."

You can reduce it by applying more pressure on the gas pedal .

Okay, enough joking around. Go back to the dealer and please keep us updated.

If it helps:
Damage caused by a surge (lightning strike) can be proven by (1) a local thunderstorm recorded by a weather service, and (2) visible traces on the vehicle or abnormal conditions of the on-board electronics. It was probably not a direct lightning strike, but rather about 50 meters away; otherwise, you would have experienced a concussion.
The car dealership should have scanned and documented the condition of the vehicle's onboard electronics. It's clear that several control units (ECUs) have been incorrectly programmed.

I would try to limit the extent of the damage by (this is where the car dealership failed; once your report is complete, they should have contacted the manufacturer from the beginning to discuss the suspected lightning damage).
- Reading out the complete vehicle electronics and any error codes (which would be an Autoscan with VCDS).
- Check all fuses.
- Comparison of target values and actual values for all ECUs.
- Actuator diagnostics;
- Temporary replacement of all suspicious ECUs (the workshop must approve this);
- Inspection, especially of the cable harness connecting the MSTG (Main Switching and Control Gear) to the motor (there is a test box for this).
- If possible, disable and unregister all control units (ECUs) that are not required for vehicle operation.

The trading frenzy was nonsense, especially considering the likely cause. Hopefully, you didn't have to pay anything for it.

hg
Herbert.

"Has the pressure regulating valve been replaced? It's working again now. I've driven about 500 km and everything is okay, no error messages."

Has the pressure regulating valve been replaced again?
In the first post, you already wrote:

Andyvr666 wrote:

Sensors and pressure regulating valve replaced from the rail

.

Overall, I would have expected such a valve to be relatively immune to electromagnetic interference (EMI), especially if it's only powered by 12V from the control unit and doesn't have its own internal electronics. Therefore, I am even more surprised by this error.

No, it was replaced back then, but when it stopped working, the old one was put back in. Now that it's running and displaying an error message about high rail pressure, the new one was installed, and it's been working ever since.

Hopefully, the repair has finally been successful this time.