TPS issues on a 02 Jeep Liberty,

[Tempest]

P0123 High voltage at TPS.

Intermittent. Vehicle stalls when CEL occurs. Will restart and run.

Graph on code reader seems to indicate smooth operation of TPS. No obvious spikes or dips in the range. Reader only shows %, not actual voltage. Goes from about 12% to 78%.

Weird part: With key on, connector voltages are:

4.64 V, 7.2 mV, 5.16 V Shouldn't there only be voltage at one of the wires?

IAC was changed by a mechanic that said it was the problem (on a road trip at the time). Car ran better for a few days and then the same code returned.

Any help is much appreciated.

 

[eljefino]

If you're probing with the computer plugged in you're essentially leaking current through the computer and the DVOM you're using is so sensitive it picks it up.

You have a scratchy pot on the TPS, throw a new part at it. It'll be scratchy at idle where it spends a lot of time.

The computer occasionally sees a throttle position that's falsely not at idle, and then decides it doesn't need to move the IAC as part of its strategy. Then you stall.

The only other issue is if you have other sensors on the line that can corrupt the pure +5v feed.

 

[Lubener]

Disconnect the TPS and check its operation with an analog ohm meter. It is nothing more than the volume control on an old tv or radio.

 

[Chris142]

I have put 3 or 4 tps on my jeep over its lifetime. The one from oriley has lasted the longest

 

[meep]

TPS Sidebar: While the '02 may still be a potentiometer, I was interested to discover the newer chryco TPS are no longer. On the '08 model I opened up, the rotary portion had no contact to the board. Looked like some sort of field-effect device but I really couldn't tell as there wasn't much to it, no supporting circuitry. Cool design but I couldn't understand how it functioned, BUT- in later years they have gone away from a pot.

 

[The_Eric]

Originally Posted By: Tempest
P0123 High voltage at TPS.

Intermittent. Vehicle stalls when CEL occurs. Will restart and run.

Graph on code reader seems to indicate smooth operation of TPS. No obvious spikes or dips in the range. Reader only shows %, not actual voltage. Goes from about 12% to 78%.

Weird part: With key on, connector voltages are:

4.64 V, 7.2 mV, 5.16 V Shouldn't there only be voltage at one of the wires?

IAC was changed by a mechanic that said it was the problem (on a road trip at the time). Car ran better for a few days and then the same code returned.

Any help is much appreciated.


First thing- reading the output with a graphing scan tool really doesn't show the whole picture. They simply don't sample fast enough to catch all the things that can happen. Ideally you would back probe it and sample with a quality lab scope. Using an old style analog meter may do better- it's worth a try. Read both resistance (unplugged) and output voltage.

The connector voltages are weird- are you measuring with the connector plugged in or unplugged?

 

[zzyzzx]

http://www.obd-codes.com/p0123

I would blame the wiring or bad electrical connection someplace before I would blame a part.

 

[Chris142]

The tps grounds through the clock spring. I have replaced that too. I think I have replaced 4 tips in 150k. Its usually the tps that fails.

 

[Tempest]

Thanks all for the help.

I was reading the voltages with the connector unplugged from the sensor, not being back probed.

This is the original TPS with about 150K on it. Wouldn't hurt to change it anyway. I think I'll try that and report back with results.