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Replacing AW4 Transmission...FML

IF YOU DISCONNECT THE CONNECTOR FROM THE PCM YOU HAVE NO POWER AND NO SWITCHED GROUND TO THE SOLENOIDS.

BACKPROBE those wires to find out what the pcm is sending and recieving to the solenoids.

1. Check that the solenoids have power going to them.
2. Check that the pcm is grounding the correct solenoid at the correct time.


Why not take it to someone who knows what they are doing? Just sticking those probes into the connector isnt exactly kosher, either. It can screw up the terminal and cause even more problems....
 
If your having issues with a solenoid it is going to affect 2 gears, not just one. It sounds like you have an internal transmission problem.

Replacing the one you have with an /extremely/ cheap used transmission is asking for issues.

Have it rebuilt or buy a used one that will come with some sort of warranty.
 
IF YOU DISCONNECT THE CONNECTOR FROM THE PCM YOU HAVE NO POWER AND NO SWITCHED GROUND TO THE SOLENOIDS.

BACKPROBE those wires to find out what the pcm is sending and recieving to the solenoids.

1. Check that the solenoids have power going to them.
2. Check that the pcm is grounding the correct solenoid at the correct time.


Why not take it to someone who knows what they are doing? Just sticking those probes into the connector isnt exactly kosher, either. It can screw up the terminal and cause even more problems....

You don't need power to the solenoids to test the resistance in the circuit. Testing the resistance is the recommended way to test them for function.
 
If you are close to NW florida, shoot me a pm, im a r&r/diag guy at a nationwide trans shop. We offer a free diag service that will at least let you know for sure wether the problem is internal or not.
 
You don't need power to the solenoids to test the resistance in the circuit. Testing the resistance is the recommended way to test them for function.

What he was testing for in the picture was for 12v while the pcm was disconnected from the solenoids.

To test resistance for each solenoid, you need to use the pos and neg from the solenoid itself, NOT an external ground.

And to TRUELY test their function, take the solenoid out of the valve body, have one person blow into the opening on the solenoid while another applies a ground and 12v to it. It will click and change from allowing air to pass, to not allowing air to pass.

And fwiw, even after testing solenoids this way (and checking resistance) we have still had solenoids cause problems.
 
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IF YOU DISCONNECT THE CONNECTOR FROM THE PCM YOU HAVE NO POWER AND NO SWITCHED GROUND TO THE SOLENOIDS.

BACKPROBE those wires to find out what the pcm is sending and recieving to the solenoids.

1. Check that the solenoids have power going to them.
2. Check that the pcm is grounding the correct solenoid at the correct time.


Why not take it to someone who knows what they are doing? Just sticking those probes into the connector isnt exactly kosher, either. It can screw up the terminal and cause even more problems....
first of all you are wrong. Turn, if you will, to page 8W-31-7 of your 96 XJ factory service manual. Please observe that the grounds for the three solenoids and the output speed sensor do not go through the connector that the TCU plugs into (C132.) In fact since you refer to a PCM I am not sure you actually know what you are talking about with XJs. The only XJs that have a PCM instead of a TCU and an ECU are 2.5L equipped ones, this is a 4.0L / AW4 combo and has separate trans and engine computers.

Please note that the ground for those three solenoids and the output speed sensor is circuit Z1, an 18ga black wire, and that it leads from the connector for the trans harness (C135) via splice S123 to ground G105, located on the left inner fender wall.

Backprobing is a good idea but not necessary here.

What's this "check that the PCM is grounding the correct solenoid" thing you speak of? Are you even passingly familiar with XJ transmission control? The XJ uses positive side switched solenoids, one side of all the solenoids is permanently grounded (as I explained above) and the other side is switched to 12V to activate the solenoid. On 97 and later vehicles this is done using a Sanken SI5154 intelligent fault detecting positive side switch in a TO220-5 package; I'm not too familiar with the 96 and earlier TCU internals but it should be roughly similar, or possibly just a simple PNP positive side switching configuration since the 96 and earlier do not detect solenoid wiring faults automatically. I have one in the yard, I'll pop it open tomorrow and do some basic reverse engineering on it for curiosity sake.

What he was testing for in the picture was for 12v while the pcm was disconnected from the solenoids.
no. No, he wasn't, read the thread. He was checking solenoid resistance to ground, just using the meter incorrectly (DCV instead of ohms, common new DMM user mistake.)

To test resistance for each solenoid, you need to use the pos and neg from the solenoid itself, NOT an external ground.
technically you are correct, but once you check to make sure the grounds are OK, it's a fairly accurate test and will find at least 75 out of 100 bad solenoids.

And to TRUELY test their function, take the solenoid out of the valve body, have one person blow into the opening on the solenoid while another applies a ground and 12v to it. It will click and change from allowing air to pass, to not allowing air to pass.
yes, again, technically correct but generally AW4 solenoids fail electrically and at that point it's best to just replace all three with brand new ones while you are in there.

I would also like to reiterate /supposedly/ only having an issue with overdrive slipping.
nope. Read the thread, he was having issues with 3rd and possibly OD slipping.

A bad solenoid will affect 2 gears, NOT JUST ONE.
correct. Looking at the shift solenoid table for the AW4 it looks like this is probably not a solenoid issue, but it can't hurt to spend a few minutes probing with a multimeter to find out if there is a simple to fix issue before blowing a bunch of cash on a replacement transmission.

After the amount of flat out incorrect info you've used as a basis for your arguments here I am not sure I would trust your diagnosis, cost estimates, or quality of work at your shop. I'd recommend taking it to a shop that is familiar with jeeps, preferably familiar with XJs as they are one of the few jeep models to ever use the AW4/A340, or at the bare minimum, a shop that employs people who spend a few minutes looking at the schematics for the vehicle in question before flying off the handle and telling multiple people with years of experience working on and experimenting with XJ transmission electronics that they are wrong.
 
first of all you are wrong. Turn, if you will, to page 8W-31-7 of your 96 XJ factory service manual. Please observe that the grounds for the three solenoids and the output speed sensor do not go through the connector that the TCU plugs into (C132.) In fact since you refer to a PCM I am not sure you actually know what you are talking about with XJs. The only XJs that have a PCM instead of a TCU and an ECU are 2.5L equipped ones, this is a 4.0L / AW4 combo and has separate trans and engine computers.

Please note that the ground for those three solenoids and the output speed sensor is circuit Z1, an 18ga black wire, and that it leads from the connector for the trans harness (C135) via splice S123 to ground G105, located on the left inner fender wall.

Backprobing is a good idea but not necessary here.

What's this "check that the PCM is grounding the correct solenoid" thing you speak of? Are you even passingly familiar with XJ transmission control? The XJ uses positive side switched solenoids, one side of all the solenoids is permanently grounded (as I explained above) and the other side is switched to 12V to activate the solenoid. On 97 and later vehicles this is done using a Sanken SI5154 intelligent fault detecting positive side switch in a TO220-5 package; I'm not too familiar with the 96 and earlier TCU internals but it should be roughly similar, or possibly just a simple PNP positive side switching configuration since the 96 and earlier do not detect solenoid wiring faults automatically. I have one in the yard, I'll pop it open tomorrow and do some basic reverse engineering on it for curiosity sake.

no. No, he wasn't, read the thread. He was checking solenoid resistance to ground, just using the meter incorrectly (DCV instead of ohms, common new DMM user mistake.)

technically you are correct, but once you check to make sure the grounds are OK, it's a fairly accurate test and will find at least 75 out of 100 bad solenoids.

yes, again, technically correct but generally AW4 solenoids fail electrically and at that point it's best to just replace all three with brand new ones while you are in there.

nope. Read the thread, he was having issues with 3rd and possibly OD slipping.


correct. Looking at the shift solenoid table for the AW4 it looks like this is probably not a solenoid issue, but it can't hurt to spend a few minutes probing with a multimeter to find out if there is a simple to fix issue before blowing a bunch of cash on a replacement transmission.

After the amount of flat out incorrect info you've used as a basis for your arguments here I am not sure I would trust your diagnosis, cost estimates, or quality of work at your shop. I'd recommend taking it to a shop that is familiar with jeeps, preferably familiar with XJs as they are one of the few jeep models to ever use the AW4/A340, or at the bare minimum, a shop that employs people who spend a few minutes looking at the schematics for the vehicle in question before flying off the handle and telling multiple people with years of experience working on and experimenting with XJ transmission electronics that they are wrong.

It is impossible for two people to agree on everything but fortunately/unfortunately I do. Years ago when my AW4 acted up, I took it to 3 different automatic transmission specialist nethier of whom were able to tell me what the problem was but was able to recomend a multi-thousand dollar replacement. A simple OHM test at the engine room connector pointed me to 2 of the three solonoids which I replaced in my driveway. It was 100,000 transmission miles ago. One test probe to the XJ body or engine and the other to the solonoid wire in question and read the resistance.

To the OP, I have come to beleive you could get more accurate help here on this forum that say 90% of the transmission shops out there. If all else fails, get a used low milage replacement with a warranty.
 
To the OP: if one or more of your solenoids is bad, you can get used ones from the yard for much cheaper than buying new.
 
Blank-Picard_Facepalm.jpg

ohms vs volts
 
So then if checking my solenoids at the harness near the TCU isn't right where should I do it? The black and gray connector near the trans dipstick?
 
Won't matter, either one is fine. You *should* get the same measurement - same color codes on the wires.

I suspect your solenoids are bad, but I'm not sure if replacing them will fix all the problems.
 
Won't matter, either one is fine. You *should* get the same measurement - same color codes on the wires.

I suspect your solenoids are bad, but I'm not sure if replacing them will fix all the problems.

Should I get used ones from a Junkyard or buy them online?
 
If you are pulling them yourself at the yard, bring your DMM and measure them before pulling, make sure you aren't pulling a known bad set. I would pull two sets actually (if they put the vehicles up on stands anyways - it would suck to pull more than needed if they are lying on the ground), they probably won't charge you much. You can get a new pan gasket + filter kit to install at the same time (since you'll need the gasket anyways) - it's ATP part number B112 available on rockauto or amazon for around 25 bucks shipped.
 
That's the one!

With the pan dropped you can test them with a 12 volt battery (even a little lawn/garden battery will work.) Negative to the transmission housing, positive to the connector on the solenoid, you should hear them click. You can check resistance the same way - meter probe to transmission housing, other meter probe to the connector.
 
That one has a cork gasket that will require rtv but otherwise should be fine. If you are going to do that I would really just rtv the pan like the factory did though - the reason I like the rubber gasket is you can use it a few times if you are careful and dropping the pan frequently for a while (I.e. if replacing the solenoids doesn't help, or to check the solenoids before buying replacements.)
 
who makes the "better rubber gasket?" I got one from Carquest and it seemed OK, not sure if it was all rubber or rubber coated cork but it was just rectangular cross section. Works OK but don't know if I would trust it for reuse. Is there one similar to the Fel-Pro valve cover gasket? I know that Lube Locker doesn't make one. However it seems like less of an issue for the AW4 because the screen isn't that fine and there's a drain plug... is it really a problem to do a drain and fill periodically without inspecting the screen (assuming that you changed it sometime within the past 100K miles)
 
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