42RLE transmission acting goofy with P0700 code

I think that you should inspect the wiring harness as I’d suggested previously. Look for chafing in the loom. If you find areas where it’s rubbing, open the loom up for closer inspection . The wire you’re looking for is dark green and white.

No need to buy a new relay for testing, just swap with the horn relay.

Alright, the split loom near one of the transmission plugs crumbled when I started touching it but the wiring underneath appeared to be ok. I ran a continuity test from the PCM connection to the pin on the transmission plug for solenoid circuit and it came up good.

What are your thoughts at this point? Still a possible wiring issue? If so, how can I test for it since continuity came up good?
 
Did you ever plug in an external code reader as suggested to see what the underlying transmission code is under that catchall P0700?

My inexpensive external reader from Harbor Freight Tools showed a P0755 code indicating a bad 2/4 solenoid which got me rolling toward the fix. After lots of reading about that code I ended up replacing the solenoid pack, the check balls in the valve body, range selector switch, and installing a Stage 1 shift kit from Transgo. Amazingly some combination of those four things I replaced/installed fixed the transmission and it has been problem free for well over two years now. The object with the pastel green ring on the right edge of the valve body is the solenoid pack.

I'm not saying this is what would fix your transmission but at least get an external code reader plugged in to see if the underlying codes will point you in a specific direction as did mine.

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Did you ever plug in an external code reader as suggested to see what the underlying transmission code is under that catchall P0700?

My inexpensive external reader from Harbor Freight Tools showed a P0755 code indicating a bad 2/4 solenoid which got me rolling toward the fix. After lots of reading about that code I ended up replacing the solenoid pack, the check balls in the valve body, range selector switch, and installing a Stage 1 shift kit from Transgo. Amazingly some combination of those four things I replaced/installed fixed the transmission and it has been problem free for well over two years now. The object with the pastel green ring on the right edge of the valve body is the solenoid pack.

I'm not saying this is what would fix your transmission but at least get an external code reader plugged in to see if the underlying codes will point you in a specific direction as did mine.

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Yes, sir! P0750 is the transmission specific code mine is throwing.
 
Yes, sir! P0750 is the transmission specific code mine is throwing.
Thanks I missed that post.

Lots of posts on that issue at https://www.google.com/search?q=P07.....69i57j0l4.7399j0j8&sourceid=chrome&ie=UTF-8

Possible causes
- Low transmission fluid level
- Dirty transmission fluid
- Faulty Low Reverse solenoid valve
- Low Reverse solenoid valve harness or connectors
- Low Reverse solenoid valve circuit is open or shorted

Sure sounds like it could be the solenoid...
 
Lots of posts on that issue at https://www.google.com/search?q=P07.....69i57j0l4.7399j0j8&sourceid=chrome&ie=UTF-8

Possible causes
- Low transmission fluid level
- Dirty transmission fluid
- Faulty Low Reverse solenoid valve
- Low Reverse solenoid valve harness or connectors
- Low Reverse solenoid valve circuit is open or shorted

Sure sounds like it could be the solenoid...
Agreed, but I’m a rookie just learning as I go. I intend to order the solenoid pack tonight if I can’t find a different cause. Is there anything else you recommend I replace while I’m in there? I did a trans flush and new filter around 2-3 years ago.
 
Agreed, but I’m a rookie just learning as I go. I intend to order the solenoid pack tonight if I can’t find a different cause. Is there anything else you recommend I replace while I’m in there? I did a trans flush and new filter around 2-3 years ago.
I dunno. Despite indications the problem was caused by the solenoid pack, I replaced a couple extra items like the transmission range selector switch, check balls, and installed the Transgo shift kit just because I didn't want to have to go through the ordeal again for something inexpensive and easily replaced while it was apart. You'll be replacing the filter and ATF+4 again. :)
 
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Replaced the shift solenoid pack and TRS switch, test drove for about an hour and so far so good! I don't fully trust it yet, but I trust it enough to take it to work tomorrow which should give it a decent number of miles.

I didn't do check balls or shift kit because I was little intimidated to open the valve body any more than I already did.

I also installed a UCF extra clearance skid since I had the shovel off anyway and freaked out a little when I had a clattering letting off the gas around 45+ mph but then realized it was probably just u-joint since I don't have an SYE yet. Put stock skid back on and everything seems good.

I'll update again after driving more or if the problem comes back.
 
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Alright, calling it fixed. Put over 100 miles on it last week without issue. It's up on jack stands again but that's just to install an SYE and new drive shaft.

Sorry for hijacking thread and thanks for the help!

To summarize for anyone else stumbling across this with a google search:

- 2005 LJ with auto 42RLE
- P0750 code with limp mode.
- Tried resetting PCM but problem returned after 45 minutes of driving, had to get trans warmed up.
- Did continuity test from PCM to L/R solenoid pin and found no problems.
- Replaced solenoid pack and transmission range selector switch.
- Drove for a week and about ~120 miles without issue.
 
Hey all,

I've been trouble shooting a check engine light for awhile on a 2000, 4.0. I picked up an OBD reader and it is showing the P0743 code. I don't notice any issues shifting. Originally the check engine light would come and go. I was able to clear fault by disconnecting the battery and it would be all good. Now it's steady on. Cleared PCM and it came back. I picked up a replacement transmission control relay as it is the least expensive starting point. I looked in fuse box in engine bay and there is nothing labeled for the relay I would like to replace. Can anyone tell me where the I should be looking before rip jeep apart.

Learning one issue at a time.
 
I'll do more troubleshooting but I'm short on time and wanted to get that part on the way. I have had occasional hard shifting from 1-2 when cold back in the winter and after talking to Mark it seemed a likely enough possibility that my PCM is failing that it's worth ordering and testing it out.

The 20 minute drive definitely wasn't enough to convince me either, but it was enough combined with talking to Mark that I went ahead and ordered the part. I'll update this thread as I progress through troubleshooting and certainly when I find the culprit.

Edit: I legitimately appreciate yours and everyone else's input on tracking down possible causes.
Hi, wondering if you ever found the culprit on this one? Thanks, Dave
 
Hi, wondering if you ever found the culprit on this one? Thanks, Dave
If you're asking about the Hard 1-2 shift, it's a common thing on the TJ.
You might want check out Wranglerfix.

Side note - Code 0750.
I recently replaced the solenoid pack on my WJ (grand cherokee).
It seems to have fixed my transmission issues.