2004 Jeep Grand Cherokee , Code P0122 Set, Runs Poorly Sometimes

This 2004 Jeep Grand Cherokee came in with the complaint that the engine would buck and jerk and sometimes stall. There was a code P0122 stored and the TPS had already been replaced in an attempt to repair this vehicle. The customer stated that the oxygen sensors and the crank position sensors had also been replaced due to codes being set for them as well.  I did a little investigating and found a problem with the wiring harness at the rear of the engine slightly to the driver’s side of the vehicle. If you look at the wiring harness at the rear of the engine in the next picture you should be able to see that it may be resting on a stud extension on the last head bolt.

If you enlarge the next picture and look in the mirror reflection you can get a slightly better view.  Lifting the harness and securing it away from the stud could be enough to alleviate the concern temporarily.

To fix it, a little more work is needed.  I actually did not find the problem until I did some testing at the TPS. At the TPS connector the orange/red wire is the signal wire to the PCM from the TPS The orange wire is the five volt reference from the PCM to the TPS and the black/lt blue wire is the sensor ground. Looking at the data on my scan tool showed a TPS voltage of zero volts. I jumpered the five volt reference wire to the TPS signal wire. The scan data voltage should have gone up to five volts but instead remained at zero. The diagnosis would have to be either the TPS signal wire shorted to ground or a faulty PCM. Following the wires around and lifting the harness, in the previously mention suspect location, caused the TPS data voltage to increase to 5 volts. Diagnosis shorted TPS signal wire.

The plastic housing that mounts on top of the throttle body assembly needed to be removed so that I could easily access the TPS connector and wiring. It also needed to be out of the way for repairing the wiring harness.

There were several mounting screws and hoses that had to be detached  from the housing.

The only one that is slightly tricky is the one for the rubber boot that sealed between the housing and the throttle body bore.  The clamps for the air intake tube also need to be loosened so that connection point can be disassembled.

A view of the same screw from the underside.  Even with loosening the clamp the boot may stay on the throttle body or the housing.

To get enough room to work comfortably, I also moved the hoses and cables shown in the pictures out of the way. I had to carefully cut the old split loom and tape off of the wiring harness. I lifted the harness shield that runs the length of the engine off of the head bolt studs. This allowed me to maneuver the harness around enough to work on it without having to fully remove it.

I had to cut a short section out of the orange/red wire.

I repeated the repair on a second wire that I found damaged also.  I used heat shrink tubing to seal and protect the splice joints.

This is the damage on the underside of the original split loom. A combination of heat and vibration against the stud over several years is what damaged the loom.

I cut a new piece of split loom to length.

Installed the loom and re wrapped with tape.

I cut a short piece of rubber hose to use as a protector over the stud.

It will probably never happen, but if the harness works it’s way back down again the rubber hose will keep the wires from shorting out on the steel stud.

Except for installing the breather housing back onto the throttle body this one is done.  Notice that the rubber sealing boot is on the throttle body. I took it off and installed it back onto the plastic housing before the final assemble.

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