2004 Jeep Grand Cherokee Laredo 4.0L 6 cyl P0122

Jeep has been running rough intermittently but now rough running becoming more frequent. There is one code stored, a P0122, which I believe freeze frame showed was at vehicle speed 50mph or so. Backprobed connector to Throttle Position Sensor, 5V reference shows good with key in ON position,  and good ground. Signal wire increases gradually from 0.6V with throttle fully closed to 3.8V with throttle fully open. Gradually decreases from the 3.8V back smoothly down to 0.6V at closed throttle. Behaves same when I test this way while tapping on the TPS. The main concerning result to me is the 3.8V reading,  I understand reading at WOT should be about 4.5V. Am I correct in calling a faulty TPS? Or do I have more work to do?  Thanks guys, Pop
 

Hey pop! It's tough to say if you have more work to do or not since the problem is intermittent and probably not happening right now. But, if you're gonna try a part, a TPS for this Jeep isn't terribly expensive.

I wouldn't sweat the voltage range, necessarily. Not all TPS sensors will go to 4.5V at wide open. For what it's worth, the P0122 set criteria is pretty straightforward:

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1.3 seconds is a long time for a TPS sensor signal to be stuck low. I'd also keep an eye out for a misrouted harness or a rubbed wire. The harness runs along the valve cover gasket bolts/studs, and it's easy to get one of the studs in the wrong place... 

Thank you, Tyler! I cannot find any evidence of either heat or vibration damage to any of the wires. I hate to just be a parts changer, but I am going to go ahead and replace this TPS sensor while I am in here. I did notice some dirt in the throttle body. Is it safe to clean it out with throttle body cleaner with the unit still installed on Vehicle? Thx, Pop

 

Sorry I didn't get back to you sooner, Pop. You're probably way ahead of me, but yes, totally safe.

You might also see what reset options your scan tool gives you. That generation of Jeep had several reset functions related to idle, minimum throttle position and such.

Thanks, Tyler. I am glad to report that the TPS replacement has cured the driveability problems and code has not returned. Thanks again!