What's wrong with my transmission?

[jeremyj]

1996 XJ
4.0L
auto (AW4)
4x4

So when I got the thing, it had 155K on the odometer and second gear was completely gone. I replaced the transmission with another AW4 with only 60K on it. The Jeep worked perfectly for over a year. Now...not so much.

Here's what's going on. First, after long periods of highway driving, it would downshift to third gear and stay there. I would shift it manually into any other forward gear and it wouldn't leave third. Neutral, reverse, and park all worked fine. I realized that all I had to do was turn it off and then back on and the problem would immediately go away. Since it didn't take any cooling down, I assumed it was an electrical problem. But then it pretty much stopped happening.

Now, it hasn't done the downshifting thing for a while. Instead, there's a 500 RPM variation thing happening now. When I'm on the freeway, doing 60 mph or more, the engine RPM is about 500 rotations higher than it used to be. If I hit the gas just a little bit, it goes down 500 RPM. So it's constantly jumping and falling about 500 RPM as I'm going down the freeway. My guess is the torque converter.

So what the hell is going on? Any ideas? Should I go through all the sensors and swap them with the ones from my original tranny? Maybe try to replace the TCU? I'd like to avoid yanking the transmission again, but if the TC is in fact dying on me, I don't see a way around it.

 

[lawsoncl]

Grab a multimeter and start doing some tests. http://www.transonline.com/transdige...ers/index.html. In particular check the resistance of the solenoids.

I'm leaning towards a bad TPS myself as giving it more gas is making the lockup kick-in. It's probably not a bad shift solenoid as the shift solenoids are not engaged for 4th gear.

 

[jeremyj]

Yeah, I'm 90% sure it has nothing to do with the solenoids.

Oh, and I should add that there are no codes being thrown.

 

[joe_peters]

1. Adjust the throttle pressure cable.

2. Adjust the shifter cable.

3. Adjust the NSS.

4. Test the TPS.

Post up results.

 

[Ecomike]

Sounds like a TPS going bad to me too. They are easy enough to test.

 

[kastein]

A 96 will not throw codes for the solenoids, just tossing that out there. Only 97 and later check for the existence of the solenoids, 96 and earlier just hope they are there and drive as if they are.

Sounds like TPS, solenoids, TCU, or TPS to me. Wire some indicator lamps to the solenoid drive lines, label them, put them on the dash or passenger seat, take it for a drive. I have the same torque converter lockup issue right now but I replaced my TPS recently, the transmission a few months ago (previous one was FUBAR.)

 

[larue2000]

I have had a similar problem (see Sick AW4) and thought I had it nailed with testing solenoid 3 (TCC) as bad. But before I spent the money to change out the solenoids, I installed a toggle switch that goes around the TCU and hardwires Sol 3. Worked like a charm - when the TC unlocks at 55-60 mph, I flip the switch and it locks up and never waviers. Solenoid 3, testing bad, functions as good.

This is not a perm solution. I've merely narrowed the list a little. Seems like it has to be the TPS, TCU or vehicle speed sensor. With depressing the accelerator temporarily solving the problem (indicating the TPS) that is inconsistent with the fact that it doesn't happen at speeds under 45 mph (indicating the VSS). I climb a hill ever evening that's about 2 miles long. It's a 35 mph speed zone so I never get above 45. But the vehicle will lockup right on schedule at approx 42 mph and maintain lockup until I hit the break to turn. All this is after just experiencing the falling out of lockup on the freeway.

BTY, the hardwire of Sol 3 in not a useless exercise - it can be useful for decending steep grades at a slow speed. There is a writeup on this or similar forum about "1st gear lockout and torque converter control". Pretty interesting. The diode he uses, which is never spec'ed out, is a P600M.

 

[1984jeep]

Hey guys, Same problem here too, 1996 with 107 thousand on it. Same symptoms etc, transmission shop checked everything out and replaced the TPS. So thats new, problem not solved. We tested the solenoids directly, they all measured around 12.8, good. tonight checking the TCU wiring and things like that. I have found the ohm readings for what these should be on this and other forums, I will let you guys know what the readings are tonight and what they should be.

 

[1984jeep]

So in turned out it was the Solenoids, not a hard fix. The most annoying thing about the whole job is the 19 bolts in the pan, also what might suck is if you don't have a drain plug. Mine does. really nice to have. Put the solenoids in. I now have 111,170 on it and it has been working juuuuust fine. Shifts a little smoother too. I found a kit of all 4 solenoids for under 200. For that price I would recommend trying the solenoids before you get a new transmission.

 

[SleeperXJ]

Thanks for posting your fix.

 

[lawsoncl]

So in turned out it was the Solenoids, not a hard fix. The most annoying thing about the whole job is the 19 bolts in the pan, also what might suck is if you don't have a drain plug. Mine does. really nice to have. Put the solenoids in. I now have 111,170 on it and it has been working juuuuust fine. Shifts a little smoother too. I found a kit of all 4 solenoids for under 200. For that price I would recommend trying the solenoids before you get a new transmission.

4 solenoids? The AW4 only has 3. There is a FAQ I posted on here somewhere with the toyota part numbers for new solenoids and a source.

 

[jeremyj]

Old thread bump. I'm glad to hear that a solenoid swap fixed at least one person's issues. That's typically not the fix for others with this problem. I've read a few threads where they changed the solenoids and the torque converter lockup issue remains.

My lockup issue is getting worse, lately. The problem typically shows up when I've been driving for a while. It seems to act up more frequently when I've got a lot loaded in the Jeep and/or the temperature is hot. I've changed all the sensors, the TCM, adjusted the cables... nothing works. I guess I will try the solenoids next. I have new fluid, but I'll need to pick up the solenoids, a filter, and a new gasket. I was trying to avoid dropping the pan.

If anyone else has some fresh input, I'd appreciate it.

 

[lawsoncl]

Have you measured the resistance of the solenoids yet? I would have done that before throwing the other parts at it. Should be 11 to 15 ohms if I remember correctly. A bad one will usually be way off. The filter is basically a metal screen which can be cleaned off instead of buying a replacement. Your call on buying a gasket or just using atf resistant permatex.

 

[jeremyj]

I've read more than one person testing the resistance of the solenoids and finding them to be normal. They end up changing them anyway, and the problem goes away. I don't know what the deal is with this, but they can test normal and still be defective somehow.

 

[lawsoncl]

I've read more than one person testing the resistance of the solenoids and finding them to be normal. They end up changing them anyway, and the problem goes away. I don't know what the deal is with this, but they can test normal and still be defective somehow.

True, they can be intermittent when they get hot and good resistance doesn't prove they are good. I usually suggest checking the resistance hot and cold because it's a quick and easily check that can confirm a bad solenoid.

Can you refresh us on what you've tested and replaced already? Your earlier comment that the throttle affected the lockup would indicate testing out replacing the tips is in order. They do wear out and the common symptom is lockup issues.

 

[lawsoncl]

Your earlier comment that the throttle affected the lockup would indicate testing out replacing the tips is in order.

Dang autocorrect.

Your earlier comment that the throttle affected the lockup would indicate testing and possibly replacing the TPS is in order. Another common issue with lockup is the brake switch.

 

[TRCM]

Same with mine (also a 96 w/165k).................kickdown adjustment, new TPS, & new brake switch made no difference.

 

[jeremyj]

The TPS is new, I've swapped out the transmission computer from under the passenger kick panel, I've adjusted the cable on the TB bracket a few times, and I have the correct fluid and a new filter in it. The fluid is at the proper level, looks clean as the day I put it in, and doesn't smell odd. The brake switch looks and works perfectly.

My most recent adventure leads me to believe this is a heat related failure. The lockup issue has been super active for the past month or two. This has been the hottest summer ever up here; it's been over 80 degrees pretty much every day, since early June. The lockup issue historically only happens after long drives at 60+mph, when everything's nice and hot. Now it's happening after just a few miles of highway driving, with the temps in the 80's.

Just yesterday, it was about 95 degrees and I was cruising on the freeway with the AC on. The tranny dropped into neutral and wouldn't let me accelerate anymore. I pulled over and ran through the gears. 1-2, N, and R all worked normal, but it refused to go into three or four. When in drive, it would go from first to second and then it would dump into neutral, which limited me to about 25-30 MPH. I was only about a mile from my destination, so I crawled to the place and shut it off.

After three hours of sitting in the shade, and with the temperature dropped into the low 80's, I started it up and drove it home without any loss of gears. I also drove to work this morning without drama, except both times, toward the end of the drive, it started to shift with some hesitation. Almost like it wanted to dump into neutral again, but it never actually does. It doesn't feel like slipping at all to me. It's more like a gear change hesitation. It's weird. Also, I don't have carpet in the Jeep and the tranny tunnel seems to be slightly hotter than normal. It could be my imagination, given the fact that I'm being ultra sensitive to everything, but it's really cooking after about twenty minutes or so.

I'm going to go ahead with replacing the solenoids (and the fluid and filter again). I also have access to an aftermarket tranny cooler that I might throw in for some extra cooling. This heat seems to exacerbate the issues, so it can't hurt to swap in a bigger cooler.

 

[kastein]

Yeah, this is one of those cases where bad resistance means they're definitely bad but good resistance doesn't mean they're good. Same story with the CPS ohm meter test (not related to transmission function.)

 

[lawsoncl]

Just yesterday, it was about 95 degrees and I was cruising on the freeway with the AC on. The tranny dropped into neutral and wouldn't let me accelerate anymore. I pulled over and ran through the gears. 1-2, N, and R all worked normal, but it refused to go into three or four. When in drive, it would go from first to second and then it would dump into neutral, which limited me to about 25-30 MPH. I was only about a mile from my destination, so I crawled to the place and shut it off. .

That sounds more like a failing t/c or internal hydraulic issue or just serious overheating. Both shift solenoids are off for 4th gear and both are on for 2nd.