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TPS woes


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Hello all, newbie online member.

A month ago went into Limp mode without any CEL's and had fault codes for the TPS. Replaced it, they came back. Shop replaced the alternator, regulator, and battery thinking a voltage fluctuation might be responsible. Codes came back. Changed out the throttle body for good measure. Now they are back. The shop is otherwise reputable, known for racing more than anything I guess, and they are big on the 993's. But an electrical issue I've found drives most shops nuts. With $5K into this repair already though I don't want a fishing expedition.

Any obvious answers left? Porsche manual basically says if TPS error code, replace TPS. The only thing left upstream seems to be the harness and ECU. Should I go there next? Any easy diagnostics?

After the TPS was replaced, it happened less often and with 100 miles in between faults. Meaning the older sensor seemed to fault more often if that is a clue.

Any and all help appreciated.


The PO had an early version aftermarket kit put on with k28's, upgraded exhaust, and a chip based tune.... dreading it's related to that.

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Sorry, obvious oversight.

2001 996 TT

p2135 Porsche Fault code 256 - accelerator pedal potentiometer

p0121 Porsche Fault code 427 - accelerator peral potentiometer. 1

Not sure its relevant but also have k28 turbos, early fabspeed exhaust, hi-flo cats, etc. And chip tune.


Edited by syncrofly
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Interestingly when I go to the "actual values" tab for the two "pedal potentiaometer encoders" in the durametric it looks like with a pedal neutral position the two have different starting voltages. The first has .72 and 4.26v respectively, the sensor is new so I assume this normal. When broken down by percentage it seems an angle of #1 is 3.9% while the other is at 4.3% and varies similarly over a range of pedal motion. meaning close but not the same nor consistently different, but always slightly off. Guessing that's all normal?


Edited by syncrofly
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I did the battery unplug reset hoping that the neutral position wasn't being registered in the right location by the ECU. Need to get it out on the road and drive it 100 miles see if I still have the same issue, I assume I will as the shop would have done the same thing during install as I had battery replaced.

Advice still welcome on any diagnostic recommendations.


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  • 3 years later...


Related to P2135 and P0122,

I have a 02, 996 GT2 and I'm experiencing similar issues. 


Any update on how this was fixed or if you found the solution?


I have already replace the Pedal Sensor with a brand new unit, still having the issue. Now will check the TB, which ground point should i check??


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