can low voltage cause TPS codes? P0121
 

Was using the search feature and never saw a definitive answer.

Occasionally I will get a P0121 code. Don't drive the car often but noticed it happened twice today. Cleared code and car runs fine. When code is active, car shifts funny.
I only mention low voltage cause sometimes my factory volt gauge is showing like 10 volts while I'm driving. No under drive pulley is on car, any ideas?

Suppose it's possible (sorry can't tell ya for sure). Are the 2 occurring at the same time? You could always check voltage at the battery with a multimeter when the dash is reading 10 volts to see if it's a valid reading or not. If so, time to deal with that issue first.

When you put the cam in, did you (or the tuner) change the TPS vs RPM Test Lower {C3907} in the idle range? That causes P0121 in cammed cars if not changed...

TPS should be fed 5V from the PCM and you'd really have
to sag the IGN voltage for that to go out of regulation.

First thing to do is measure / scan your raw TPS voltage at
key on engine off and at idle.

Thanks guys, I have noticed and it may not mean anything that it only seems to do it when I'm running the A/C. It coded the P0121 on the way to the drag strip the other night, I cleared it and turned the A/C off. Drove the other 30 miles to the track and it never came back on. Drove it to take the kids to the movies earlier and had the A/C on, came on within 10 miles of driving. UGH

I get the same code when I have my AC on too I also get a MAF low voltage code. I think I just need some fine tuning since I got my cam put in and its still the first tune.

Which wire on TPS do I need to probe?

As previously stated, tps operates on a 5 v reference. Most vital sensors in an engine operate at less then 12 volts specifically for this reason.

Did you try recalibrating the sensor?

Just checked and have 5v key on engine off and at idle. I have recalibrated sensor, and this is the 3rd TPS on the car, same problem with them all

Have you tried reading the tps percentage with a scanner to see if it runs full range? 0-100% normally I would ask if you adjusted the throttle plate set screw but properly recalibrating the sensor resets the tps percentage back to zero regardles of the throttle plate position. I have seen tps codes thrown for other issues also. Can you get ahold of a GM service trouble tree ffor thar code?

% sweeps 0-100%

Was the table changed like I mentioned way back in post #3...

I bought the car already done, but did have it tuned. I will call the tuner tomorrow and see if he can dig up my file

listen to what was asked did your tuner chaNge the parameters for p0121 min,max MAP? THATS MOST LIKELY WHAT IS DOING IT

Talked to the tuner and he pulled up my file and said yes the parameter was lowered. Said if the car is running fine besides the code we may have to turn it off so it can't code that one.

Without seeing it it would be hard to say. I'm about a 3 hour drive from them, so it may be a few weeks before I can get it to them to look at it.