99 XJ Transmission Issues

I've had a P0740 and a P0740 PENDING code/s for the past 6 months. Had the transmission (AW4) rebuilt 3 times, luckily 2 were under warranty, we had another shop check wiring and replace the transmission wiring harness. I myself have tested the TPS, replaced the TPS, tested the solenoids at the engine bay transmission connector, the solenoid connectors themselves, and the TCM. The TCM and ECU were rebuilt as trying to fix this issue. I also did a visual inspection from the engine bay transmission connector to where the wires enter the transmission.

The transmission performs awesome when trailing and at highway speeds. I do notice sometimes it doesn't always go into overdrive/lock-up but it does 95% of the time. Sometimes upon startup and shifting from 1st to 2nd, it will sputter and run like an o2 sensor is going bad(No other codes). I shift it into N and rev it slightly and back into drive and it's back to normal. I also did a fluid change while testing the solenoids and made sure it was Dex/Merc as I know these AW4's are picky with the fluid. I'm absolutely stumped and can only think of the torque converter being an issue? There is also a whine type noise when in D or R from the transmission. Related to the T/C? I need to fix it so I can pass emissions. Any advice would be awesome.

I don't think the problem is the ATF, I have never used the factory recommended ATF and have always used AMSOIL. The only time it had factory fluid was when I drove it off the lot but that all changed after the first 20 miles!
https://www.naxja.org/forum/showthread.php?t=1159116

Thank you for your input, but I'm not sure the fluid is the issue. Any other ideas? It's going into the shop on Monday to get a upgraded torque converter installed in hopes that that will fix it but just wanting to see if anyone else has had this issue and could help fix/diagnose it?!

There is no TC "upgrade" for the AW4!

Since the trans and been in/out a few times, check that the bellhousing bolts are still tight. If they've backed out, that messes up the crank sensor alignment, and usually first shows up as stalling when you put it into gear.

Here's my search thread from 2yrs ago!
https://www.naxja.org/forum/showthread.php?t=1157442

lawsoncl I'll check that out. Any ideas on the P0740 code/s?

Just got home from the gym to find 2 codes relating to the O2 sensors. I knew something was up with them. Found a blown fuse in the PDC and will be replacing it tomorrow. That should fix the sputtering issue I've been having. As for the transmission code, it seems to lockup/overdrive all the time now. Starting to wonder when the TCU was "rebuilt" the code was "engraved" into it or something. I tried disconnecting the battery for over an hour to reset the computers as some people have said it would clear the codes until they come back if they do. And as soon as I connected the battery those codes were there. That's why I'm thinking TCU? Let me know your thoughts.

The AW4 is controlled by about 5 different sensors. I'd look at the brake light switch, the NSS, and the TBS. I might also, look at the CkPS (crank Position Sensor).

Check that O2 wiring and make sure it's not up against the exhaust manifold. Had someone post recently about the trans wiring being worn through under a wire clamp on the side of the trans as well (I think it was the rear output speed sensor wire). A stuck-on brake light switch will also cause the TCU to no lockup too. It's possible for the solenoid to test okay resistance-wise, but still be sticky or broken.

I've checked and replaced the brake light switch already. I'll take a look at NSS, TBS and CPS. As well as the rear speed sensor wiring. I'll post what I find.

There are two speed sensors. I took it from your original post, that you tested them. This last post is that you will be checking the wiring. On my '98, I had issues. The trans would not have 1st gear, then shift to second inconsistently. It did a bunch of stuff. Finally, I replaced the rear output seed sensor. That did the trick. My neighbor did a scan test. The speed sensors he could not do. But said it was probably the rear one, as he could not test it.
Also, did you unplug the TC, and drive it? Does it shift manually, good. If so, then it is probably electrical. Be warned that it will not down shift. And you'd need to slow down to shift into lower gears. Sort like a manual trans.

I haven't tried driving it with the TCM unplugged. I'll try that tonight after work. Do I use the 1-2 and 3 selectors as the "manual" gears? And I have a solenoid kit I was going to return. I might install them on Sunday if the manual shifting doesn't work. The solenoids seem to be the fix for most people with this code. But ill replace the rear output speed sensor as well just to see what that does. Ill let you know how it all goes.

problematicxj said:

I haven't tried driving it with the TCM unplugged. I'll try that tonight after work. Do I use the 1-2 and 3 selectors as the "manual" gears? And I have a solenoid kit I was going to return. I might install them on Sunday if the manual shifting doesn't work. The solenoids seem to be the fix for most people with this code. But ill replace the rear output speed sensor as well just to see what that does. Ill let you know how it all goes.

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Yes, use the 1-2 and 3 for the manual gears. As before, there is no 'breaking' from the trans and motor in this. So, the breaks are needed to slow down.
Also, you can test the Speed sensors in the vehicle, as I understand. From the plug up by the trans tube, were you can t4est the solenoids, use an analog Ohm meter. The two on the side are for one on the speed sensors. The other two on the bottom are for the other. Need to raise the rear tires. They need to be spun. With I think the trans in gear. Should get some blips. The removal of the rear speed sensor is fun. That bracket doesn't have a large enough access hole.

So I tried the manual shifting and it drove pretty well. Starting to wonder if the TCM could be the issue? everything else I've tested seems to be where it should be as far as resistance and condition upon visual inspection. I found one on eBay is it something to try?

75SV1 said:

Yes, use the 1-2 and 3 for the manual gears. As before, there is no 'breaking' from the trans and motor in this. So, the breaks are needed to slow down.
Also, you can test the Speed sensors in the vehicle, as I understand. From the plug up by the trans tube, were you can t4est the solenoids, use an analog Ohm meter. The two on the side are for one on the speed sensors. The other two on the bottom are for the other. Need to raise the rear tires. They need to be spun. With I think the trans in gear. Should get some blips. The removal of the rear speed sensor is fun. That bracket doesn't have a large enough access hole.

Click to expand...

Couple of clarifications. With the TCU unplugged or the fuse pulled, you also don't get t/c lockup. I think his speed sensors are fine since it's shifting and not getting other codes. I've never actually seen a bad 98+ speed sensor, and it' always been damaged wiring. There's not much to go wrong with them as they are literally just a coil, versus the older sensors being a magnetic reed switch.

Think it could be the TCM? I've tested just about everything I can and it's all come back good. I'm getting the TC replaced tomorrow because idk if that was replaced when the tranny shop did a "rebuild". Any more ideas would be helpful.

It's possible the TCM has an intermittent problem, just not very common.