ESP comes on when engine warmed up

I've got a 2001 A3 1.6 (new style) that has a weird problem, but cannot find anyone else mention it on here so here goes..

When the engine is cold, she starts fine. I can drive till the temp gauge creeps up to 90, and a couple of minutes after that, the brakes seem to lock on for a just a second, before the ESP light comes on, but also putting the car in limp mode.

If you switch the car off and back on again whilst still warm, it struggles to start although the starter motor sounds like its running normally. It now has flashed up the EMS light too.

The only things to change recently is that I have had four new tyres and a wheel alignment done about a month ago, and the other thing was most likely a sticking thermostat as the temp gauge used to bounce between 90 to 110 regularly but seemed to correct itself after a couple of days of this (this happened only a week or so ago) - Could these be related?

I'm reluctant to take the car to Audi just yet as I'm guessing this will end up being a big bill! If i can work on it myself, I'd prefer to give that a try!

Any thoughts?

i had sort of the same prob on a vauxhall vectre it was just a wire not connected once i found it and pluged it backin it was fine just took a bit of time as it looked as if it was connected just a thought

Update:

I've unplugged the MAF to see if that had any effect, but it ran exactly the same way as beforehand. I left the engine running from cold, and it stalled once it had warmed up (rather than me thinking it was the brakes coming on).

Could it be one of the ABS sensors that puts the car in limp mode? I dont know under what circumstances the car is put into limp mode when the ABS light comes on, so anyone with this info would help me no end.

I've ordered a code reader, so as soon as I have some fault codes I'll update again..

Cheers

Update 2:

I've plugged in a code reader and got these two outputs:

4082 - Bank 1 Probe 1 Electrical Fault in current circuit
4142 - Engine Speed Sender G28 No signal

... any ideas??

This only comes up once the engine is warm - It runs like a charm until it warms up!

You unplugged the MAF, which should have come up as a fault code! I don’t recognise those code numbers, I only have P and VAG code lists but Bank 1 Probe 1 is the lambda sensor in front of the cat which looks as though it is faulty and the engine speed sensor code is self explanatory. Do these two codes keep coming back?

Quote:

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Originally Posted by Crasher

You unplugged the MAF, which should have come up as a fault code! I don’t recognise those code numbers, I only have P and VAG code lists but Bank 1 Probe 1 is the lambda sensor in front of the cat which looks as though it is faulty and the engine speed sensor code is self explanatory. Do these two codes keep coming back?

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Yeah, I plugged the MAF back in before I read the codes and then did the code reading.

If the engine is cold, resetting the codes is fine. After a short drive the rev counter briefly drops to zero and the car stutters, and then it goes into limp mode showing both the EMS and ABS lights on the dash.

I thought that a faulty speed sensor would cause a continuous fault rather than just the one until it cuts into limp mode. How easy is this sensor to replace? Ive spoke to GSF who say they do not supply the part - is it known as something else? They have a Crankshaft sensor that is about £50 - that sound reasonable?

Im getting proper narked off with this car now..

The crankshaft sensor is the same part as the speed sensor, PM me your cars reg and I can tell you the part number. From the codes you are getting it is quite reasonable to change both the speed and lambda sensors but remember that other faults on the car, such as a HT circuit misfire (crankshaft speed variations) and faulty AMM (too rich or too lean), can cause those two codes to appear. If I had VAG or P codes for those faults and your cars details, I could be of a little more help. Don't get annoyed with the car; your inability to diagnose and repair the fault is not the cars fault. Modern cars are extremely complex and difficult things to diagnose faults on and can tax even the professional so have patience and work your way though this, getting annoyed with it won't help.

Quote:

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Originally Posted by Crasher

The crankshaft sensor is the same part as the speed sensor, PM me your cars reg and I can tell you the part number. From the codes you are getting it is quite reasonable to change both the speed and lambda sensors but remember that other faults on the car, such as a HT circuit misfire (crankshaft speed variations) and faulty AMM (too rich or too lean), can cause those two codes to appear. If I had VAG or P codes for those faults and your cars details, I could be of a little more help. Don't get annoyed with the car; your inability to diagnose and repair the fault is not the cars fault. Modern cars are extremely complex and difficult things to diagnose faults on and can tax even the professional so have patience and work your way though this, getting annoyed with it won't help.

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Cheers for all yourhelp on this, much appreciated. I've PM'd you my car details..

He crankshaft speed sensor is VAG part number 06A 906 433 L and costs £82.14 from Audi and comes with a two year guarantee. I have had problems with non genuine crankshaft speed sensors so for the price difference I would go genuine.

The lambda sensor is a common failure and is part number 06A 906 262 AN and costs £126.67 and the same goes for the lambda sensor where suppliers are concerned, I try to fit genuine sensors if possible.

If these both keep coming up as faulty it is quite reasonable to suspect the ECU is correctly identifying them as faulty. One of your symptoms strikes me as being a faulty coolant temperature sender but your car has the mapped cooling system electronic thermostat and these are showing signs of being unreliable.