Help needed...What should I do next?

[mikeheff]

Thanks in advance to any suggestions/help anyone can give me. I have a 1996 Tahoe that keeps getting code p0121 (throttle position sensor circuit A low output) I have replaced the tps with genuine ac delco part, checked voltage , grounds. I installed a new connector on tps, rewired it straight to pcm in correct terminals, soldered wires. I did this in case there were a wire rubbing in harness that I couldn't find. Still get code ! I got a used pcm with same serial number as original. I plugged it in and runs rough, I assume it will need reprogramming. Does anyone agree replacing pcm is the only thing left? nothing else left in that circuit that I know of. This is getting frustrating to say the least, so if anyone has experienced this please give me some good advise.

 

[SunlitComet]

if nothing is wrong with the tb or cables themselves then replace the pcm and reprogram for proper drivetrain setup.

 

[mikeheff]

if nothing is wrong with the tb or cables themselves then replace the pcm and reprogram for proper drivetrain setup.

Thanks, I am taking in this Thursday for programming. Is it normal for the donor pcm to run very rough until programmed. I got one that had same serial # as mine, but off different vehicle they told me.

 

[SunlitComet]

if same drivetrain then it should not be an issue. but perhaps yours came off an engine with a different engine size. and it is part number not serial number.

 

[mikeheff]

You would be correct, I called the used yard I got it from and they said was off blazer with 4.3 L.

 

[SunlitComet]

so yeah it isn't exactly firing on all 8.

 

[mikeheff]

Thanks again for your help, I will post how its doing after the programming later this week

 

[mikeheff]

Ok guys, I finally got the ecm programmed at GM dealership. The same problem is there, sets tps code low voltage. I'm lost! new genuine tps, rewired straight to ecm, replaced ecm and programmed. any ideas? even GM had no positive input.

 

[mikeheff]

today I put on new coolant temp sensor, just cause t shares ground with tps. I also installed new ac delco spark plugs, just because, I knew this had nothing to do with tps problem, but why not, right? I double checked all pins and still, The Damned TPS code still comes back, runs like dog pooping razor blades when you accelerate and shifts hard 1-2. Any ideas folks...I'm lost once again

 

[SunlitComet]

how does the pcm data output on temperature reading compare to the dash? are the grounds on the thermostat housing in good shape as well as engine to frame to battery?