Posted: 8/31/2010 4:21:09 PM EDT
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My wife was driving our 99 Jeep Cherokee 4.0 I6 and the SES light went off. She said when she pulled in the driveway, the RPM's started rising and the motor was "running higher". I took it to O'Reilly's and had them scan it, and it returned a p0121 code something about the TPS sensor (which could explain the weird surging idle problem my wife experienced). I was wondering if anyone had this error before, and what fixed it?
After doing some googling, it looks like swapping out the TPS fixed it for some, but for others they were on a wild goose chase trying to figure out what it was doing. |
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TPS should only be ~$50, and is something you can replace yourself. Easy enough, and a pretty common item to fail. If you replace the TPS, and still have problems, you're not out a fortune, and your car has a new TPS, which was probably going to take a shit soon anyway. |
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Quoted:
TPS should only be ~$50, and is something you can replace yourself. Easy enough, and a pretty common item to fail. If you replace the TPS, and still have problems, you're not out a fortune, and your car has a new TPS, which was probably going to take a shit soon anyway. Yeah, but I was doing a quick search on my iPhone at O'Reilly's and it wasn't as cut and dry as I expected so I thought I'd come home and get some more input on it. I have no problems swapping out a TPS. 
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all signs point to the TPS senor. 
take care of it its as easy as unscrewing it.. this happened to my caddy,, i held off replacing it cause it was 90 bucks, one day I had to STAND on the brakes to keep from ramming into the car in front of me at the red lights, when i replaced it the comp did its thing and reset it good as new after that |
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Or you could check it before throwing parts at it.
The orange wire is your 5v reference,the brown/yellow is ground,and the orange/dark blue is the signal return. Key on,engine off,you will see 5v (or very close) on the orange wire and around .5v on the orange/dark blue.As you open the throttle by hand,the voltage on the orange/dark blue wire should increase steadily until around 4.5-5.0volts at wide open throttle.At no time should it drop down as you increase the throttle opening.Easier to see on a scope,but a volt meter should work good enough. Since no other codes are showing up,and most of the sensors share the 5v reference voltage and grounds,unless you have a broken wire,you have a bad TPS. |
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I am impressed that the normal bags of douche haven't arrived to describe the following: "I had an XJ that did something similar..." "My YJ never had that problem...." "If I ever had a BJ then I wouldn't care about such, but here I am with my XJ that never had that problem either...." |
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I am impressed that the normal bags of douche haven't arrived to describe the following: "I had an XJ that did something similar..." "My YJ never had that problem...." "If I ever had a BJ then I wouldn't care about such, but here I am with my XJ that never had that problem either...." It's early yet.................. 
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Quoted:
Or you could check it before throwing parts at it. The orange wire is your 5v reference,the brown/yellow is ground,and the orange/dark blue is the signal return. Key on,engine off,you will see 5v (or very close) on the orange wire and around .5v on the orange/dark blue.As you open the throttle by hand,the voltage on the orange/dark blue wire should increase steadily until around 4.5-5.0volts at wide open throttle.At no time should it drop down as you increase the throttle opening.Easier to see on a scope,but a volt meter should work good enough. Since no other codes are showing up,and most of the sensors share the 5v reference voltage and grounds,unless you have a broken wire,you have a bad TPS. Well I went and bought a new one prior to seeing your post. It idled really odd at first after swapping them out, surges and drops, etc. I drove it around for about 10 minutes and it seemed to normalize a bit there towards the end, but I'd need to drive it more to really tell. It seems like when in drive and at a stop idling, the RPM's are lower than before. The tach says 400-500, give or take, but I'm not sure how accurate the factory tach is anyway. When in Park at idle, it's around 800-900 and seems pretty normal. Does the computer need time to "relearn" the new sensor? |
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Quoted:
Quoted:
Or you could check it before throwing parts at it. The orange wire is your 5v reference,the brown/yellow is ground,and the orange/dark blue is the signal return. Key on,engine off,you will see 5v (or very close) on the orange wire and around .5v on the orange/dark blue.As you open the throttle by hand,the voltage on the orange/dark blue wire should increase steadily until around 4.5-5.0volts at wide open throttle.At no time should it drop down as you increase the throttle opening.Easier to see on a scope,but a volt meter should work good enough. Since no other codes are showing up,and most of the sensors share the 5v reference voltage and grounds,unless you have a broken wire,you have a bad TPS. Well I went and bought a new one prior to seeing your post. It idled really odd at first after swapping them out, surges and drops, etc. I drove it around for about 10 minutes and it seemed to normalize a bit there towards the end, but I'd need to drive it more to really tell. It seems like when in drive and at a stop idling, the RPM's are lower than before. The tach says 400-500, give or take, but I'm not sure how accurate the factory tach is anyway. When in Park at idle, it's around 800-900 and seems pretty normal. Does the computer need time to "relearn" the new sensor? Yeah,some can take a little bit of learning-most of the time it's quick.Drive it around and see if the code comes back. |
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Take the pos battery cable off for half an hour and it should reset the computer. My XJ had the same issue after getting the engine submersed while 4 wheeling (I had a snorkel on it). Replaced TPS and still had an issue. Called a friend and told me to pull power from the computer to reset it. Worked fine after that. And I didn't get a BJ for having an XJ but I got into my PJ's later that night.
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Quoted: Take the pos battery cable off for half an hour and it should reset the computer. My XJ had the same issue after getting the engine submersed while 4 wheeling (I had a snorkel on it). Replaced TPS and still had an issue. Called a friend and told me to pull power from the computer to reset it. Worked fine after that. And I didn't get a BJ for having an XJ but I got into my PJ's later that night. Then stop being a DB and explain what an XJ is? AH. |