Mechanics

CODE P0123

2003 Jeep Grand Cherokee • 4.0L 6 cylinder 4WD Automatic • 106,000 miles

CEL on, codes p0122 & p0123, try to clear codes and 122 clears 123 will not clear. Vehicle runs terrible, hesitates, trans doesn't seem to shift at correct points, sometimes almost stalls, idle rpm will jump to 1500 rpm and then settle down to 750 or so. I have another almost identical Jeep (different color), so I swap out the TPS.
No change. And the TPS works fine in my other vehicle. Notice that the cruise control will not work, light on dash comes on but the cruise will not engage. Decided to swap out clockspring. No change. The clock spring works fine in other vehicle.
The vehicle had an open air bag recall that needed to be taken care of, so I called dealer made appt. For the recall knowing he would have to put DRB111 scan tool on to check safety system when he was done with recall repair. I asked him to check P0123 code while he had tool hooked up. He came back and said the connector on the TPS was cracked and that was what was causing the problem. I was skeptical to say the least and even more so when he told me he wanted $268.00 to change the connector. So I went to another dealer and bought a new TPS connector and soldered it in place. No change on the p123 code and I still cannot clear the code. With FSM in hand traced out the circuits and decided to disconnect the horn and cruise control connector from the clock spring. (Note horn worked before I disconnected) I was now able to clear the P0123 code, drove the vehicle and it drives perfectly. But with limited electrical capability I don't know what to do next. I know the IAC, MAP, TPS, CKP, CMP, sensors all seem to be tied to the same 5-volt supply from PCM and the grounds I believe are common also. I just don't know where to start to find the bad wire or wires or confirm one of the cruise control switches is the culprit. Any guidance would be appreciated.
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Wags1026
March 14, 2014.




First thing to do is clean the throttle plate on both sides and iac hole. Make sure all carbon is gone near tps. This however could also be a bad pcm or a short going to pcm. One thing to lso check is that these 4.0L engine rub through the harness at the rear of cylinder head by a stud tha t is there. This may also be the problem so check that. It may be causing all your problems. The ground is on the right side of engine its' a blk/wht and blk/tan wires. But check that harness that may be allof your problems.

Tiny
Hmac300
Mar 14, 2014.
Thanks for response, IAC slot and throttle body were thoroughly cleaned.
Don't think it's pcm but very well could be a short going to pcm. I suspect it's either a wire from cruise control switch, the cruise switch itself or a wire rub under hood area. I have a DVM but in my unelectrical hands it may as well be a hot potato. Really need detailed electrical advise on how to go about finding switch, wire or sensor that is causing problem. At least now I can drive it, just no horn and no cruise.

Tiny
Wags1026
Mar 14, 2014.
Make sure to check that harness where I said that is a very common fault. You can plug the items in one at a time to see which one gives your the problem
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Tiny
Hmac300
Mar 14, 2014.

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