PLEASE HELP!! AW4 ISSUE

I have a 1990 XJ and the aw4 tranny does not always shift into first or third. When i first start the jeep it is in first but once it shifts out it does not shift back down. Sometimes it shifts to third but it is not common.

Check the trans fuse @ your fuse box. And also check the TCU fuse and the TCU itself about mid way on passenger side behind the lower dash plastic. Easiest to remove the screws and pull it out. If anything, try shifting manuall as is and with the TCU disco'd. THe AW4 is elect. controlled. But you should be able to shift it manuall, but you will not have 2nd gear. Also, do a search on how to adjust the TPS and also adjust your TV cable.
Check your trans fluid, idiling in park. Make sure level is correct.

The TV cable has been adjusted and the transmission control box has been replaced. I checked both fuzes and they are not blown. Also the fluid and filter has been replaced and it still does not shift manually.

Have you tried to shift manually with the TCU disconnected?

i haven't, i didn't know you could do that. Ill try it now and see what happens.

Ok, so i tried shifting manually with the TCU removed and it shifted into all gears except second... Not sure how to get it from first to second but it wasn't doing it by itself.

selmanryan said:

Ok, so i tried shifting manually with the TCU removed and it shifted into all gears except second... Not sure how to get it from first to second but it wasn't doing it by itself.

Click to expand...

Shifting to 2nd is automated from engine rpm, load, etc. (the TCM and PCM are connected sending information to each other)

I've only done mostly transmission maintenance on the AW4, replacing fluid every so often, haven't had to remove, replace or overhaul. Has close to 200,000 miles, still running well, haven't had any problems as of yet.

Here are some initial preliminary diagnostics, things to inspect.

Check Fluid Level
Check Fluid Condition

Inspect harness connectors for corroded, damaged, loose or backed-out terminal pins.
TCM
TPS
Solenoids
TRS (NSS)

* Also you might want to inspect and clean the grounds, around the TCM where it's grounded to the body. There are other grounding points that can potentially effect the transmission and shifting. The TCM, TPS, Solenoids and TRS all have ground connections. I can't remember off-hand exactly where.

Shifting works basically from the solenoids opening and closing fluid valves.

Solenoid -- #1 --- #2 (are used for shifting)

1st Gear -- ON --- OFF
2nd Gear - ON --- ON
3rd Gear - OFF --- ON
4th Gear - OFF --- OFF

Solenoid #3 is used for the torque converter.

Could be something simple, mechanical or electrical that needs repair, cleaning or adjustment.

Shift cable, throttle cable and shift lever needs to be adjusted correctly for the transmission to shift correctly. I remember needing to make a few adjustments to the shift lever and cables.

Possible causes found in a manual, related to shifting problems.

electronic controls faulty, valve body faulty or valve body solenoid faulty, throttle cable faulty

Thanks guys, will check these things and get back with you.

What fluid did you use? I had a major problem with my tranny (slipping, not shifting right, other issues I can't explain) after I put in ATF+4 as recommended by autozone, I drained it all and put back in dex/merc works so much better. Just a thought.....

It kinda sounds like a bad solenoid in the transmission. They are easy to change.

Drop the trans pan (beware there will be fluid in the bottom, it does not all drain with the plug) and you will see 3 solenoids there with electrical plugs. Swap them from a set in a junkyard trans.

Don't buy new/rebuilt aftermarket ones, they are junk. :/

I don't feel that it would be a solenoid because the tranny shifts when the TCU is not plugged in.

The solenoids are not used, at all, when the TCU is not plugged in.

Thats why you don't get 2nd gear.

Part of the information I found about the AW4 operations:

When solenoid plungers #1 and #2 are energized solenoid plunger moves from seat, opening drain port, releasing line pressure. When either solenoid (#1, #2) is de-engergized plunger closes drain port.

Solenoid -- #1 --- #2 (are used for shifting)
---------------------------------------------------------------------
1st Gear -- ON --- OFF ( drain port closed)
2nd Gear - ON --- ON (drain port open, line pressure released)
3rd Gear - OFF --- ON (drain port closed)
4th Gear - OFF --- OFF (over-drive, #3 de-energized = drain port open - releases line pressure, #3 energized = drain port closed)
(drain port open = valve unseated, drain port closed = valve seated)

If your getting 1st, no second or third points toward #2 solenoid not functioning correctly.
The valves appear to be ok, if you're able to shift manually without the tcm and solenoids.

I haven't worked on and thoroughly studied how the AW4 operates, so my understanding is limited. With around ~200,000 miles I probably should find time to read through the AW4 manual. I usually wait until something fails and then try to figure it out while trying to do the repair.

Im getting second and OD. First usually works when I first start the Jeep and put it in D but once it goes into second it doesn't downshift back to first. Sometimes from a dead stop it feels like its in first and as soon as I hit the gas it goes straight to second.

Drop the pan and test your solenoids then. But, chances are like Cal said, it's failing.
Do you know 100% which gears you are actually getting? Other than when you shift manually with TCU disco'd
Maybe find a JY TCU and swap that.

I'm going to swap my TCU with an 89 XJ and see what happens and ill post it up.

I'd give it 99.5% not a TCU problem.

People love to throw it out there as the problem, but it so rarely is that its almost (almost) not worth testing.