AW4 transmission minor service - should I replace the solenoids?

[Motorhead X]

My MJ started having occasional hard shifts, especially up to the top gear. It was overdue for a fluid change at 35K miles, so I did a quick 3 qt. drain and refill, which helped some. I'm now going to drop the pan to replace the filter and do a larger fluid change. Should I change the solenoids while I'm in there? I ordered them from Rock Auto, but now I'm wondering if the solenoids either "work or don't". Shifting points seem fine and the occasional clunky, hard shifts are more present at lower rpms. If I'm gassing it, they seem to shift a bit smoother. Thanks. 

[Dzimm]

You should honestly do other troubleshooting before jumping to the solenoids.  It really doesn't seem like the solenoids are a very common issue on the AW4 so it would be best to leave them alone until you narrow it down.

 

First thing I would do is reset the ECU.  Disconnect the positive battery terminal and touch it to ground for 30 seconds or just leave the battery disconnected for a while or overnight so all the capacitors drain.  This should reset all the sensors and allow it to "relearn" over the next 50-100 starts/drives.  May not fix it but it's a free, no effort way to see if it fixes it.

 

Next would be to do a resistance test on the solenoids from the wiring harness to make sure they are in the proper range.  I believe there is also another test on these if you inject voltage to operate them but can't remember for sure.  

 

Full drain and replacement of trans fluid and filter would be good and may fix it if your fluid was bad, although if you are only 35k over the interval, it's probably not the fluid unless it's getting burned up from some other issue.  It's definitely tempting and makes sense to do solenoids while its apart so you aren't doing it twice, however I would caution putting aftermarket solenoids in if you aren't positive that is the issue.  If the factory AW4 solenoids are not the actual problem, you could introduce a new problem if the aftermarket ones are no good.  You could always do the fluid and filter only, then if the issue still persists, drain the new fluid into a very clean/degreased or brand new catch pan so you can put it back in.  The labor twice sucks but it prevents changing parts unnecessarily and would keep each troubleshooting step separate so you'd know what fixes it.

 

 

This sounds crazy but it could also be your crank position sensor.  This damn thing creates all kinds of really weird issues that seem completely unrelated.  I actually had the exact symptoms you describe in my 98 XJ for a while that eventually developed into dropping out of gear entirely and randomly being really sluggish accelerating from a stop.  Did fluid and filter, tested and changed all the sensors on the trans even though they tested good, and tried a different TCU all seeming to fix it for a day or two but it would always come back.  It finally was figured out to be the crank position sensor.  If you do change it out, you want a MOPAR sensor because it'll just work but they are expensive and hard to find new these days.  Aftermarket ones are very hit and miss, occasionally bad out of the box and it's a crap shoot how long they will last so buy two just in case one of them is bad.  You need about 5' of extensions to reach it without lowering the rear of the trans, go in from behind the crossmember and over top of everything.  An extra set of hands is super helpful to guide the socket from up top.

[coolwind57]

Just went through transmission issues like 2 Months ago.  Mine just refused to shift.  There's several parts that affect your transmission.  Shift solenoids, TCU (Transmission Control Unit), there's a speed sensor, and the NSS (Neutral Safety Switch).  As DZIMM states, that crank position sensor may have something to do with your problem. 

 

I would not replace the shift solenoids till you test them first.  There's a continuity test that i performed on mine.  I can't remember what Olms they should shoot at so check your manuals.  I dropped the pan, tested continuity and i also took them out and hooked them up to my battery (one wire lead on the spade connector to positive and one on the housing to battery ground) and confirmed a clicking noise to mechanically test each solenoid.  Mine were good.  Saved some bucks.

 

Next on my list, I did a TCU swap after checking that the fuse that feeds it was good and that the TCU was getting juice.  Bought a used TCU off ebay and wasted my $100.  No change.  My original one was good.

 

I was having trouble finding the correct trans shift speed sensor and was in the process of ordering one when I thought I'd go ahead and swap out the Neutral Safety Switch NSS.  My NSS was only about 3-years old, so I prioritized it at the bottom of possible causes.  NSS are not expensive, I think I bought mine at under 20-bucks.  Removed and replaced and the transmission shifted as if it just rolled off the assembly line.  Couldn't believe it.  

 

Let me know if you come down to the TCU during your troubleshooting and I can send you my spare to help.  It's frustrating, I know.  I was down for over a Month.

 

Good luck, brother. 

 

 

 

 

 

 

[75sv1]

Ohms is 10 to 16 I believe. 13 nominal. You can test them at the trans plug up by the tran dip stick. Also, the brake pedal switch and the TPS. Also, I'd change the fluid a few times. On mine it was the speed sensor. '98-up has two. Also, mine was the rear one. A bit of a pain. The brake light switch does get rusty. I think $20. You can clean are relube the NSS. Hardest part is to take it off.