Not your usual 42RLE 1st-2nd shift issue

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Fred85

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Jun 2, 2021
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Virginia
First off, I think I've read everything available online about 42RLE shifting issues, PCM problems, Wranglerfix fixes, etc. Unfortunately I haven't seen anything similar to the issue I've been experiencing, which brought me to become a member of this great forum (long-time lurker).

My '06 LJ experiences a hard 1st-2nd shift/shudder only after warmed up. I've read that most shifting issues occur on a cold start, but mine only occurs after about 10-15 minutes of driving. Until then, the transmission shifts fine and there are no issues. When everything does get warmed up, the 1st-2nd shift is hard and I can best describe it as a shudder you feel through the accelerator pedal. All other shift points are fine.

The other odd aspect is that if I accelerate really slowly, 9 times out of 10 the issue does not occur. Alternatively, if I accelerate quickly (for a Jeep) it is more noticeable. I've also noticed If I anticipate the 1st-2nd shift point and back off the accelerator right when the shift happens, the issue doesn't occur.

Lastly, to throw another wrench in this, a few weeks ago I started experiencing the classic PCM issue. The engine would rev to 2.25k/2.5k RPM in 1st and then slam into 2nd. I pulled the battery cable overnight and this issue hasn't occurred again, but the usual shifting issue remains. I should add that the transmission fluid is still in relatively pink/red and appears in good condition. Thank you for any and all input!
 
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I’m going to assume that if the MIL were on you would mention it.

The 42RLE is electronically controlled with a number of solenoids and sensors. If anything is not workings properly, a code should set. The fact that you are not getting an MIL suggests the PCM is the issue.
 
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AjRagno said:
I’m going to assume that if the MIL were on you would mention it.

The 42RLE is electronically controlled with a number of solenoids and sensors. If anything is not workings properly, a code should set. The fact that you are not getting an MIL suggests the PCM is the issue.
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Actually there are a number of transmission codes that will be stored but will not illuminated the MIL. (Specifically the P0218 and P0714 temp codes associated with the PCM failure.) To the OP have you scanned for codes?
 
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That very well could still be a PCM issue, let's alert Mark at @Wranglerfix and see if your symptoms mean anything to him.

Wranglerfix.jpg
 
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@Fred85 hello Mr. Long term lurker. Your pcm is bad. The hard shift/stutter is the start of processor failure on the tcm side of the pcm. Other common failures are high transmission temperatures and all o2 sensors saying bad when good.

You can call me at 866-888-7710 to discuss in further detail.
 
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I wanted to update this thread in case anyone else happens to have a similar issue. I finally got the new @Wranglerfix PCM installed and I've been able to drive my Jeep a good bit these past 2 days (about 80 miles so far). My shifting issues are gone! It may be a mental thing, but the Jeep seems to run better now as well. One oddity I've noticed is the voltmeter in the gauge cluster now stays just below 14 V (my 2001 XJ was like this), whereas before it stayed just above 14V (like every other TJ/LJ I've driven). There doesn't appear to be anything wrong with it; just something I observed.

I'll keep this thread updated if I notice anything else in the future, but I must say I'm super excited to not have to cringe every time I drive my Jeep now!
 
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I’d be curious to know what sort alternator output readings others are getting with their WranglerFix PCM. I installed mine last August and, regardless of temp or load, the battery receives 13.65-13.71 volts. With the original PCM, the charge generally ranged from 13.9-14.1 volts but would also vary depending on load.

I have an AGM battery that was installed in December. Even though the alternator output appears low, the battery is always at 12.71 volts when I turn the engine off, then settles to 12.65 volts, so the battery is receiving the appropriate voltage.
 
AjRagno said:
I’d be curious to know what sort alternator output readings others are getting with their WranglerFix PCM. I installed mine last August and, regardless of temp or load, the battery receives 13.65-13.71 volts. With the original PCM, the charge generally ranged from 13.9-14.1 volts but would also vary depending on load.

I have an AGM battery that was installed in December. Even though the alternator output appears low, the battery is always at 12.71 volts when I turn the engine off, then settles to 12.65 volts, so the battery is receiving the appropriate voltage.
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any update to this issue? i also just installed @Wranglerfix computer and it ran good the first day and then Wednesday. i didnt drive Thursday or today but i drove it tonight to go fuel it up and get ready for work and after i cranked it up i got a check gauge light but everything looked well. so i restarted it and it was good then i went and put it in gear and got a hard shift into reverse. put it in drive and drove to the stop sign and it was in second. went down the road in second and after maybe half a mile and fooling around i got 2 codes. a p0700 and a p0622 code. after i cut it off and let it sit for a few minutes while fueling up it ran great the rest of the way. im not blaming wranglerfix's computer on it as i honestly think it solved alot of the issues. im honestly either thinking its the alternator or something maybe the battery now. it was cranking up and the volt gauge would just sit at like 1/4 of what it should be at 14 volts for a min ore 2 then it would jump up to 14 volts. im going to check the battery and the volts tomm afterwork and see what they are at
 
The computer can't fix a busted transmission, P0700 is a generic code meaning you have to get a better scanner to read deeper into the transmission. Maybe that's the first step?
 
Yea I got that much. It was throwing all kinds of codes including the p0700 before the wranglerfix swap. Now it's only throwing these 2 I'm thinking it's an electrical issue now possibly the alternator not putting out enough volts or something along those lines as it never through the p0622 code before. After it ran a bit and restarted it shifted fine so I'm positive it's not the transmission
 
Shame on me for not updating this thread again. My original issue has since returned (it actually did several months ago but I neglected to update here). Also, this Jeep gets driven maybe once a week so I've just learned to live with the problem for now; outta-sight, outta mind as they say. The good news is the Wranglerfix PCM absolutely did fix that classic high-revving-before-slamming-into-2nd shift issue, so I'm still in the Wranglerfix fan club.

Back to my original issue. Could an overfilled transmission cause this problem? I was thinking perhaps it was due to high line pressure. Perhaps a coincidence, but I just noticed my high pressure line has a very small leak at the fitting now. Any other thoughts are appreciated. Fluid is still nice and pink.
 
An overfilled automatic transmission is better than an underfilled one. I routinely keep mine overfilled by around a quart which stops it from sucking air on steep climbs.
 
Fred85 said:
I was thinking perhaps it was due to high line pressure. Perhaps a coincidence, but I just noticed my high pressure line has a very small leak at the fitting now. Any other thoughts are appreciated. Fluid is still nice and pink.
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The pressure in the cooler lines should be pretty low, I think they all use low pressure fittings and clamps like the power steering return lines. Do the lines all look free from kinks or damage? Most likely you just have a simple leak.
 
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