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Hi folks, hope everyone is staying safe. First post here.
Been fighting an issue with our 04 WJ 4.0 4x4.
Absolute random bogging down/hesitation/stumble/slight backfire if pushed.
Felt like fuel lean/starvation or exhaust restriction. Just falling on it's face.
Didn't matter temperature, speed, throttle position, open/closed loop, totally random.
Never died, never developed a dead miss, idled and revved in park and neutral perfect.
Data stream looked fine, no check engine light.
Good fuel pressure, good vacuum, blah blah blah.
Checked and re-did all grounds, man I did everything you can imagine.
I did replace a few parts that I had planned on replacing anyway, just not this soon.
Anyway, it eventually threw a pending code P1899 P/N switch issue.
I dismissed this at first, Jeep always starts, reverse lights work, figured it was a fluke.
More diagnosing, checking voltage drops, wiggling connectors, blah blah blah.
Still no engine light but I checked codes again, there's that pending P1899.
Checked the wiring diagram and noticed a P/N ground signal is monitored by the PCM.
Pulled connector off P/N switch (42RE) and it's soaked in trans fluid.
I've seen these old style Chrysler P/N switches develop leaks in the past.
I will replace it but for now I sprayed the switch and connector out real good with contact cleaner.
Plugged it back in and drove it.
I have now accumulated over 100 miles in about 6 or 7 drive cycles without a single hiccup.
Could hardly get out of our subdivision without it falling on it's face before this fix.
I am confident that the P/N switch issue was causing the engine performance problem.
Perhaps the hot feed for reverse lights was semi shorting to ground for P/N circuit and freaking PCM out?
I dunno but it's fixed and just thought I'd share, maybe this will help someone else out.
Peace :cool:

Super Moderator
566 Posts
Thank you for the write up rixdafix :) that sounds like my 04 WJ at times and also same problem my 96 ZJ is having so will have a look at the P/N switch as that also has a 42RE fitted :)
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