4.0 TPS High Voltage

[tarock]

I've got a '99 4.0 TJ that is throwing the P0123 TPS high voltage code. The IAC and TPS have been replaced with quality units. I tried to reset the check engine light, but it came immediately back on. I have back probe tested the plug with the TPS installed and voltage on the signal wire is showing 4.11v and the feed wire is 5.22v. The signal wire when applying throttle will smoothly go up to 4.98v.
I have been able to unplug the clock spring and this only lowers the voltage to 4.08v, and this allowed the check engine light to be reset. Once I plug the clock spring back in it immediately comes back on. When the clock spring is unplugged, the live data TPS % is 78. When I plug back in the clock spring it immediately shoots up to 100%.
I have cleaned as many grounds as I could find (I could be missing some) and the signal wire voltage is still never below 4.05v.
I have a new clock spring on the way, but I'm afraid this won't bring my voltage down, or am I wrong? Will a new clock spring lower the voltage, or am I seeing the correct number with it unplugged? Is there anything else I should be checking to get my signal wire voltage back into spec.?

 

[TJ Jim]

Does the tps voltage vary as you change throttle position?

 

[tarock]

Yes. It starts at 4.08v and smoothly goes up to a max of right around 5v at full throttle. So the volts sweep as the throttle is engaged. My understanding is the voltage should start below 1v and go up to around 4.3v for 100% throttle. So this is indication my TPS is starting at 78% and going past 100%
For the record, the engine runs and idles rather well. The only real reason I started tracking down the issue was trying to clear the check engine light. It might rev a little high on cold start (1800ish) and other wise it idles well. I also get a bit of rough running when starting off when cold (I just attributed that to being 25 years old and sitting for a couple years).

 

[tarock]

I actually found my old (possibly mopar) TPS lying around. I plugged it in and back tested the voltage. Down to .75v at idle which the scan tool said was 13%. Much better than the Dorman replacement that was showing just over 4v or 78%. This was tested with the clock spring unplugged. With the clock spring plugged in, the idle voltage went up to 1v.

I have a new clock spring on order. This appears to be the fix, in addition to reaffirming the need to use OEM sensors. I’ll report back once clock spring is installed.

 

[ItchyDong]

Hey, so I got coffee in me.

With the test light installed and illuminated and key in the run position, start pulling fuses 1 by 1 and watching your light. Reinstall the fuse if it doesn’t make the test light go out. This will narrow down what circuit to chase when the light goes out.

You will need the PCM connectors installed to do this and you’ll probably want to skip the PCM fuses being that you’ve already eliminated it and it’ll kill power to other circuits that may be the offender.

 

[ItchyDong]

Wrong thread