01 4.0 p0121 Code!

I'm a noob here on this forum and new(to me) XJ owner.

Its pretty stock; 3 1/2 lift, 31's, sway disconnect, exhaust, JCR sliders....pretty simple, but enough to be dangerous.:fuse:

While wheeling in Moab this last week, I took a water hole that looked ok, but turned out to be a little more than it seemed.

When I realized how deep it was I cut the ignition immediately to avoid a hydro-lock. I have a jet boat and some experience with this...

Pulled the plugs, cycled it out, dried out the intake etc....got as much water out of the oil as possible, and got it back running and off of Poison Spider Mesa in time for dinner.

Came home and have been cleaning it up, and the last thing that's screwing with me is the P0121 code.
It HAD 121 AND 123, but after a little cleaning and checking around, and flash (thanks Tim for the write up on someone else's thread) all that remains is the p0121 code.

If I clear the code, it stays off in idle. I put it in gear, and drive away and right when it feels like it should shift to second, it hesitates a bit, throws the code and will not shift. Seems to be a Limp mode, but I assume it will take care of itself if I can trace down the 121 issue.

I've read all the posts and tried the following thus far

• Re-flash per TIM (positive to ground for 30 seconds, reconnect, turn key, lights on then off)
• replaced the TPS

I do not have a meter yet, so I can't test voltage. Thats next on my list per the write-ups I'm seeing.

What I cannot find, is the part where which wire is what, and what I should be seeing on those tests.

If I could figure how, I'd throw in a couple pics for laughs....

Thanks for any help/hints...as I plug away on my submarine.

Edited to add; If i get the right voltages, whats next? And if not, what are the causes for discrepancy in voltage..?

If you got the TPS wet, and now have a P0121 TPS code, the TPS is likely toast. Several of XJ owners in my local Jeep club have dunked their TPS, and then had to replace it. The TPS has direct input to the Transmission Control Unit, so any soggy TPS signals will cause shifting issues.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives a variable input signal voltage from the TPS. It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts input. One remaining wire is the variable signal. This signal will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.

Tim_MN said:

If you got the TPS wet, and now have a P0121 TPS code, the TPS is likely toast. Several of XJ owners in my local Jeep club have dunked their TPS, and then had to replace it. The TPS has direct input to the Transmission Control Unit, so any soggy TPS signals will cause shifting issues.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives a variable input signal voltage from the TPS. It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts input. One remaining wire is the variable signal. This signal will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.

Click to expand...

Sweet thanks. Just went by harbor freight to grab a meter and will check that out next. Replaced the TPS already figuring it was a no-brainer and it SHOULD be toast..but seems it may not be since the code won't go away

If you replace any of the engine sensors, use genuine Jeep parts. Most auto parts stores sell cheap crappy Chinese parts, some that come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that aren’t faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.