Lately it feel like this truck just dosent want to be drivin. 96 12v. My latest issue started about two weeks ago. Trans is hunting 3-4 gear, yes 3-4 i know its not just lockup. Got a code of p0123 (high volatge tps). Wich explains the hunting. Changed tps out with new one no change. Finally got around to checking voltage today.... Purple to black wire is 5v as it should be. However with key on and idle position i got a reading of 66V!! From black to orange with the sensor plugged it. How can this be?!? Even with the tps plug unplugged im getting 3.2v from black to orange. Possible my computer is fried? 3.2V stays consistent all the way over to where the orane wire goes into the plug on the pcm. If you inplug that plug the voltage drops to 0. Truck is getting closer and closer to craigslist ever day lately. Any help would be great

 

A few things to try that have worked for me in the past with P0122 and P0123 codes when TPS is OK.

Inspect the JTEC connectors for water and corrosion

Clean your battery connections really good, then install ground wire from PCM directly to the negative battery connection. Is the code setting in PCM controller on R/S firewall or in ECM(engine controller)?

Vehicle Issue P0123 : 1B : THROTTLE POSITION SENSOR VOLTAGE HIGH :Replace A/C relay;Follow all appropriate diagnostics for the fault that is present. Prior to replacing parts, please review the explanation below in the recommendation field.
System or Component DTC / Error Message;Group 18 - Vehicle Performance / Driveability;Yes - Intermittent,Yes - Continuously
Recommendation Insure there are no shorts to power on the speed control 5 volt feed from switches to cav. C32 at the PCM if ok, Replace A/C relay

 

Trucks a 96. Only has a pcm no ecm correct?

 

Correct my bad, I have been seeing that code setting mostly on the 98's. But you could be getting RF noise from ALT. That's why I have been running a ground wire to the battery ground to the PCM.

 

Ok ill give it a try. Thanks for the response

 

Interesting about the a/c relay as a possible cause. Am thinking it would be nice to make sure the replacement relay has a suppression diode across the winding. I wonder if there has been an update in the replacement part.