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Mattias Sandgren

Audi TT G4+ PnP engine won't turn off (key off)

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Car : Audi TT quattro 1.8 turbo year 2000 (mfg 1999-09-20) with APX engine.

Issue : With the engine running you can turn the ignition key to off position (and remove it from the ignition lock if you want) and the engine and all lights are still running.

Pretty sure "brake + clutch drop in gear" is not going to cut it as the go-to solution for the customer. 

Is this a known issue?

The car and engine is completely standard/stock, and with the original ECU this does not happen. 

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Sounds like something is wrong on the car's wiring.

The Link ECU requires that the Main relay's positive side of the coil is ignition switched, your Audi should be ignition switched, so either its been rewired or the alternator's diode in the sense circuit is missing or shorted. The reason for this is that the Link ECU pin 3???  is connected directly to ground so with the ECU present the main relay will be switched on, however the OE ECU will not.

 

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Oh, sounds a bit like the issue I had wiring a Link Fury to an Audi RS4 -99, where the fuel pump relay was turned on as the outputs all short to ground with the ECU off.

I had to install a separate relay, powered through the ignition, in series with the ground side of the solenoid of the fuel pump relay. The fuel pump relay solenoid positive side either had current leaking through the ignition lock or it was always powered.

I'll have to check if there is a "hold" function of  sorts..

 

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Turning off the engine now works, but did a quick solution.

Out of all the "key on" signals in the car only one was found to really turn off at the key, so wiring in a relay was the best option.

There is probably some kind of "hold relay" in the car that is controlled by the stock ECU and chassis electric units, might be a signal through CAN-BUS. Also this particular model car with APX engine apparently is the only one to have this particular Bosch ME 7.5 ECU, oh well.

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