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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22919
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Im having starting problems with my A4 2006 (B7) 2L Diesel.

Customer Question

I'm having starting problems with my A4 2006 (B7) 2L Diesel. Car turns over fine but wont start. First very infrequently with up a month between incidents. Usually I just leave it for 2 or three minutes and then it starts just fine. This evening it was the worst so far. I had driven for about 20 mins on my commute home and stopped at a shop. Came out in five or six minutes and car wouldn't start. Tried for up an hour (with intervals) then got a tow truck to take me home. When I arrived home car starting fine again! So frustration!! One symptom is if the glow plug light doesn't light then the car wont start (even though) this problem sometimes occurs when the car is hot or it may happen first thing in the morning when it is cold. It seems to be more prevalent when the car is hot.
Submitted: 4 years ago.
Category: Car
Expert:  Matt replied 4 years ago.

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;
Airflow meter
Crank position sensor
Cam position sensor
O2 sensor
Throttle pedal position sensor

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Also its worth checking that the electric pump that feeds the main pump is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V