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Audi TT limp mode

Note, Manual Shift, 2001. Car has lost power, randomly, 4 times in 3 years. I pull over, turn off the car, turn back on and drive off. While driving during these events, the rpm goes to 1,000, at which point the motor flutters and the ECP light comes on. Not Chk Eng.

A scan revealed 4 codes:
-O2 sensor 16524 / PO140
-engine torque monitor 17743
-O2 sensor 16523 PO 139
-cat 16806 PO422

Note: this engine was modified. Cat converter removed. I dont have more details on the the mod other than electronic tuning was done. Car works perfectly, otherwise. 2 mechanics, one an Audi specialist, could not pinpoint the problem. Have not brought car back to the guy who did the mod.

That’s what you need to do. There is NO way for us to know what the modder did to the original car and these kinds of issues are hard enough to diagnose on an un-modified car. I’d also say the modder disabled your check engine light as all 3 of those codes would throw a check engine every time it sees them. The last 2 because there is no cat.

That said, the EPC light comes on when there is a:

  • Throttle body failure
  • Bad ABS Sensor
  • Failed brake pedal switch – Common problem on Golf 4 & Fabia
  • Bad ABS Ring
  • Bad ABS sensor wiring
  • A failed brake pressure sensor (Inside the ABS Module)
  • A Bad Engine Sensor
  • Internal engine problem
  • Power steering failure
  • Steering wheel sensor
  • Wiring issues
    And can toss you into Limp Home mode.

The Audi mechanic knows this and likely has looked for these things.

1 Like

Thanx. Will do. But how can something go wrong only one second every 2,000 miles?

Intermittent open/short.

If this is a road car, I’d put the cat and O2 sensors back on, you’re gaining minimal hp without it, and are a major polluter.


@texas has the correct answer

Especially likely on a 19 year old car with modifications. Sensors fail, the car is trying to protect itself from damage. It might also be an error cause by the mods that didn’t appear until now once the car was a bit more worn. Audi plans for that. Your modder doesn’t.

Also, agree with this advice, too, as it is illegal (federal law) whether you have inspections or not in your state.

As long as this is the case, I won’t be trying to help.


Except that doesnt guarantee a solution.

The modder is giving me details… which I’ll post here. In the end he is cooperating.

Here’s mod details:

-Apr stage 1 ecu flash

-Plus removal of cat and addition of these hardware components: exhaust, intercooler, intake, and test pipe.

They had to do something with the O2 sensor. Plenty of cars make great hp with cats. Removing them is a TERRIBLE IDEA.


With an old vehicle like this I would look for an intermittent problem with the throttle position sensor or the accelerator position sensor, these failures can be difficult to capture with the scan tool.

I think that the modifications have nothing to do with the malfunction.

Some ppl say mod isnt affecting it. They have mentioned the throttle body and poss the airmass sensor.

I sent my problem and engine codes to APR, the software company … we installed their product. Googling the APR product you can see other ppl have had the same problem. Let you know…

Altho more research didn’t reveal much, the car started idling poorly and got worse. Took it in and one O2 sensor is dead and two manifold intake hoses are very loose.