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Matt, Mechanical Engineer
Category: Audi
Satisfied Customers: 22731
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Hi. A few weeks ago I had just come off the motorway after

Customer Question

Hi. A few weeks ago I had just come off the motorway after a 20 minute journey & my glow plug light came on. I stopped & turned my engine off & when I turned the ignition again, my engine wouldn't start. AA came out & tested it & said it was my speed sensor. I was able to drive it home as it had cooked down by then. My local mechanic replaced the speed sensor & it drove well for less than 24 hours. When I was starting the engine, it was fading and shutting down after less than 10 seconds. Mechanic replaced my camshaft sensor as apparently the two are related & my timing belt was changed at the same time as it was due anyway. Car is doing the same as before, starting first time, revving appropriately but after a journey, regardless of it being long or short, when car heats up it is spluttering all over the road. Help!!! It's a 55 Audi A3 2.0 TDI Sport.
Submitted: 4 years ago.
Category: Audi
Expert:  Matt replied 4 years ago.

On any car if you get a check engine light or other fault light this typically means one or more of the sensors has failed or has a faulty connection.

The fault can be something quite simple and nothing that’s going to stop the car to something quite major that will reduce engine power and possibly stop the engine

The ECU senses this and may put the car into 'limp home' mode which typically limits the revs and the amount of power available. Usually the car is safe to drive for a short distance as the mode is intended is intended to get you home without incurring any engine damage

The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

You don't mention if a diagnostic check has been done at any point - if it has could you tell me the 'P' error codes that were logged

if the codes are consistant with engine speed sensor issues and these have now been replaced then 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 position sensor

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.

if this all checks out OK then I'd consider sending the ECU off for testing / repair