Hi. About 2 months ago my wife's TT ha an issue where the brake lights wouldn't go out. I replaced the switch and that solved the problem, but then a week later the car wouldn't start. I assumed it was due to the brake lights draining the battery (it was 6 years old). I replaced the battery and had no problems for 3 weeks. Now it won't start again. The engine turns over and cranks but no start.

I've read it might be a crankshaft sensor, but I don't have te stalling issues others have had when it was the sensor.

Any ideas?

 

If the engine cranks, then the battery and starter are good. Check for spark at the plugs, check fuel pressure with a gauge. A bad crank sensor will not give the ECM proper timing signals, and the ECM will not trigger spark. Is the check engine lamp on?

 

I guess so – a number of lights come on when I try to start the engine.

 

I assume that what z28pete is trying to say is after attempting to start the engine, does the Check Engine Light stay illuminated? If so, reading this code associated with the light could help point you in the right direction.

 

I had a crank sensor fail. No warning, no codes.

Car would start cold, but if you shut it off and tried to start it again warm, it wouldn't fire until it had cooled off enough.

Point being, don't rely on codes, check spark. If no spark on all cylinders, you have a starting place to try to solve it with the crank sensor.

 

I have read somewhere that the ECM uses the Cam Position Sensor up to 28 rpm's to start the car, then switches to the Crank Position Sensor.

I had the start cold but die hot problem which I cured by replacing the Crank Position Sensor in my 2001 TT Q 225 @ 117K miles.

I changed the Cam Position Sensor first but a really good Audi mechanic told me the CamPS hardly ever goes bad, it's always the CrankPS that is the culprit. Mine had metal pieces stuck to the magnet on it, too.

 

So I replaced one of the sensors (the easier of the two-can't remember if it was the cam or crank) and that helped for about a month, and then the car wouldn't start again. Broke down and had it towed to a mechanic and it turned out to be the fuel pump. Wasn't a cheap fix, but it wasn't something I was doing myself anyway.