Everything you ever wanted to know about the AW4

[larue2000]

1. Maybe I can add a little info to the knowledge base. Transmission problems began with an overheating event on a very hot day. One of the problems was that the darn thing wanted to grab a different gear, out of the blue, for a split second and then it would go back to where it was supposed to be based on vehicle speed and gearshift position. It felt like a loose connection - more prone to happening when accelerating and/or going around a curve. Adjusted TV cable and changed out TPS and solenoids. Then changed out the TCU, which I gave no chance of fixing the problem, and that did, indeed, fix the problem. So a bad TCU can mimick what seems like a loose wire/bad connection.

2. Referencing my post no 173 and Kastein's response in no 175, I did indeed change the VSS (obviously wasted money) and, now that I have a different TCU, I still do not have natural TC lockup from the TCU.

a. Can the OSS, which has not been changed out, affect lockup? Transmission seems to shift normal and I assume the OSS has some impact on that. Accordingly, the OSS seems to be working okay?

b. Again, the cruise control works fine so I've always assumed the break light switch was not the problem. Is there more to consider in that area?

c. There are no classic warning signs from the NSS. There isn't even a hint of a "connection" problem when starting.

d. I know that down stream from the TCU everything is fine because I've wired around the TCU for manual activation of solenoid 3 - works every time.

Regarding the fix of the final problem (TC lockup) any ideas / suggestions are welcome.

 

[Idaho XJ Guy]

Not sure if anyone has posted this up here yet and I really don't want to read through 18 pages to find out. The 91-96 AW4 actually sends NSS signals to the TCM from 1-2, 3, R, and P/N. It does not send a signal for D. I know, because I swapped a 97 AW4 into a 92 XJ and when I wired the 97 NSS "D" wire to the "D" wire in my 92 XJ, I did not have overdrive. The wiring diagrams label 3rd gear as D, when in fact it is 3rd gear. Once I disconnected the 97 NSS "D" output from my 92, and replaced it with the 97 NSS "3" signal wire, my overdrive is back!

Also, thanks for the info. I referred to this thread when doing the swap to make sure it was doable. I just wish I had known about this whole "3" vs "D" business.

 

[kastein]

I didn't post much about that because all you had to do was swap your 96 NSS onto the 97 transmission and it would have been bolt-in :dunno: I mean, you can splice if you want, but there's no need to.

larue2000 - yeah, a bad TCU can mimic basically any transmission-related sensor or actuator failure (since it's a central failure point that communicates with all of them, any wiring failure or component failure inside it that causes it to lose one of the sensors/actuators looks like an actuator failure) but the TCU very rarely fails. That's why I usually stress probing/testing with a meter to make sure you know what actually failed, rather than buying any part that appears to not be working and installing it.

 

[Idaho XJ Guy]

I didn't post much about that because all you had to do was swap your 96 NSS onto the 97 transmission and it would have been bolt-in :dunno: I mean, you can splice if you want, but there's no need to.

True... Normally. I broke my 92 NSS trying to remove it so I got to splice. The other thing worth possibly pointing out is that you've stated that if the TCM sees no signal from the NSS, then it is either in 3rd or something is wrong. In fact, it is either in OD or something is wrong. Maybe that fact will help somebody out in the future.

Still, I really appreciate all the great info in this post! Thanks Again!

 

[Digger87xj]

1. Maybe I can add a little info to the knowledge base. Transmission problems began with an overheating event on a very hot day. One of the problems was that the darn thing wanted to grab a different gear, out of the blue, for a split second and then it would go back to where it was supposed to be based on vehicle speed and gearshift position. It felt like a loose connection - more prone to happening when accelerating and/or going around a curve. Adjusted TV cable and changed out TPS and solenoids. Then changed out the TCU, which I gave no chance of fixing the problem, and that did, indeed, fix the problem. So a bad TCU can mimick what seems like a loose wire/bad connection.

2. Referencing my post no 173 and Kastein's response in no 175, I did indeed change the VSS (obviously wasted money) and, now that I have a different TCU, I still do not have natural TC lockup from the TCU.

a. Can the OSS, which has not been changed out, affect lockup? Transmission seems to shift normal and I assume the OSS has some impact on that. Accordingly, the OSS seems to be working okay?

b. Again, the cruise control works fine so I've always assumed the break light switch was not the problem. Is there more to consider in that area?

c. There are no classic warning signs from the NSS. There isn't even a hint of a "connection" problem when starting.

d. I know that down stream from the TCU everything is fine because I've wired around the TCU for manual activation of solenoid 3 - works every time.

Regarding the fix of the final problem (TC lockup) any ideas / suggestions are welcome.

B - the cruise and TCC use different circuits within the same switch. An open or high resistance in this circuit will prevent TCC lockup

 

[fsupaintball]

HEY MODS STICKY THIS

 

[Idaho XJ Guy]

NSS:
1987-1996 the NSS is the same. Positions for R, P/N, 1-2, and D. No connections indicates that the shifter is in 3rd - OR that the NSS is dirty. The TCU can't tell, this can lead to some common transmission shifting symptoms.
1997-2001 the NSS wiring harness connector is different but the internals are the same - mostly. There is now a circuit for each gear position (1-2, 3, D) on the switch and an extra wire for the new position. This was added to improve feedback to the TCU and likely also to allow the TCU to definitively throw a DTC code if it sees no contacts shorted, which now indicates a bad NSS rather than "bad NSS or 3rd gear, we don't know."

This info is from your original post, but is incorrect. Postions for R, P/N, 1-2, and 3. No connections indicate OD or that the NSS is dirty. What the wiring diagrams label as "D" is actually "3".

My point is just that it might be worth updating this info so that people don't get confused like I did.

 

[kastein]

This info is from your original post, but is incorrect. Postions for R, P/N, 1-2, and 3. No connections indicate OD or that the NSS is dirty. What the wiring diagrams label as "D" is actually "3".

My point is just that it might be worth updating this info so that people don't get confused like I did.

whoops! I somehow completely missed that in your post. Thank you very much for correcting me on that. I'll go fix it.

I think it's a confusion between the legend on the shifter bezel (OD, 3, 1-2) and what they probably call the gear positions at Aisin (OD, D, 2, 1) which would explain why D in the diagram is actually 3, and overdrive is no connections.

 

[larue2000]

Digger,
So what we think of as the "breaklight switch" has at least 2 separate circuits: a circuit for TC lockup that does not invovle the circuit(s) that turns on the brake lights and kicks off the cruise control?

BTW, this is a terrific writeup and thread. Lots of info.
Larry

 

[Digger87xj]

Digger,
So what we think of as the "breaklight switch" has at least 2 separate circuits: a circuit for TC lockup that does not invovle the circuit(s) that turns on the brake lights and kicks off the cruise control?

BTW, this is a terrific writeup and thread. Lots of info.
Larry

the BRAKE lamp switch, actually has 3 separate circuits.
one for the brake lamps- uses pins 2 & 5
one for the TCC, pins 3 & 6
and 1 for the cruise, pins 1 & 4

 

[kastein]

the BRAKE lamp switch, actually has 3 separate circuits.
one for the brake lamps- uses pins 2 & 5
one for the TCC, pins 3 & 6
and 1 for the cruise, pins 1 & 4

x2 - iirc on RENIX they only have enough terminals for the equipment installed at the factory, but AFAIK all 9?-01s (there are a few splits in there and I'm too lazy to look them up atm, I know 95/96 are the same, not sure what happens in 91-94 or 97-01) have the same switch no matter what tranny was installed or whether they had CC/NHM or not.

 

[Digger87xj]

the BRAKE lamp switch, actually has 3 separate circuits.
one for the brake lamps- uses pins 2 & 5
one for the TCC, pins 3 & 6
and 1 for the cruise, pins 1 & 4

x2 - iirc on RENIX they only have enough terminals for the equipment installed at the factory, but AFAIK all 9?-01s (there are a few splits in there and I'm too lazy to look them up atm, I know 95/96 are the same, not sure what happens in 91-94 or 97-01) have the same switch no matter what tranny was installed or whether they had CC/NHM or not.

I guess I should clarify that my statements are based on a '96, to answer larue2000's question.

 

[DayToDayXj]

Hey guys I'm currently swapping a 94 aw4 into my 97 xj. They're both 4wd units. I have came to the bittersweet situation of splicing the harness and plugs together. I cant find a diagram anywhere as to what wires are getting matched! I'm sorry if I'm posting in the wrong section but I figured I'd at least try this! Thanks guys!

 

[Eaglefreek]

Thanks for all this valuable information. I've read all pages at least twice. I'm in the process of installing an AW4 into my Eagle. Couple of questions though. First is regarding the brake sense wire. It gets grounded but when the brake is applied, ground is broken and it needs to get 12V? If so, I guess installing a XJ brake switch somehow will take care of this? Also the NSS, I assume it just grounds in park and neutral so I just hook it up to my existing NSS wire that goes to the solenoid?
Also, I would like to have control over first and second gear. Please critique this schematic, I'm not an electrical guy. Disregard the DPDT switch, I'll be using a SPDT. When the switch is in the center (off) position, the transmission will function normally. With the transmission selector in the 1-2 position and the switch in the up(on) position, post 87a on the relay will be deenergized and turn off solenoid 2 and keep the transmission in first. In the down(on) position, it will keep solenoid 2 energized resulting in the transmission staying in second. Will it work? Do I need to make any changes? Thanks in advance.

 

[BigKintheXJ]

Hello!
I just picked up a lovely 2000 xj, with a transmission that wont go into gear, and makes this terrible whizzing grinding noise. Lucky me I have a transmission from a 97 in my front yard! I read the little speal about how a 97 tcu will work as long as the extra speed sensor is left disconnected. I already picked up a 97 TCU, and am hoping to be able to get the transmission out of the jeep today so I can compare the two. I'll keep everybody updated on how it goes. I know there is very little information on this type of swap so I'll try and document as much as possible, as well as point out the differences so everything is clear.

Thanks!

Also, both are 2wd transmissions! if anyone wants to know any technical info that doesn't require opening it up, let me know!

 

[esweezey]

First off, I have not read a thread concerning the electronic control of the AW-4 that is more informative.

I believe that the problem I am experiencing is that the torque converter clutch will intermittently unlock and then lock up again and then repeat at relatively short, but irregular, intervals.

I purchased my 1996 Jeep Cherokee SE 4x4 new in 11-96. It was manufactured in 9-96. The vehicle has 243.354 miles on it. It came originally equipped with its AW-4 transmission and auxiliary transmission fluid cooler.

At normal operating temperature, at part throttle, and while maintaining a fairly constant speed on the interstate with the selector in OD or 3, the engine speed will suddenly rise approximately 250 rpm and then shortly thereafter drop to normal, just like TCC lockup during typical operation. It does not act like slippage or downshifting/upshifting. Also there is nothing actually felt when this happens, no bump, shudder or bang, just a rise and then fall in rpm. When it starts happening, the symptom occurs at varying intervals but will repeat until I pull off of the interstate and turn off and restart the engine.

IIRC, the problem began some time over a year and 5000 miles ago. At that time, I was not towing anything and the transmission was in overdrive; however, the problem most often occurs now when I am towing a trailer in third gear. (I always place the selector in 3 when towing.) One more symptom that I have not thoroughly verified (and may be irrelevant) is that I think I have noticed on two occasions that when the transmission is doing this, while at highway speed with the engine turning at approximately 2000 rpm, I can place the accelerator to the floor (WOT) and the transmission will not downshift to 2. I did not move the selector to 1-2 at those times to see if it would downshift then.

I've followed diagnostic information I've found, and using a VOM, I've tested the solenoids, the TPS, the NSS, the brake switch, the speed sensor and checked TCM voltage input and ground. Everything electrical checks out fine; however, being an intermittent problem, I assume that I have to catch the faulty component in the act of malfunctioning. I also assume that it may be possible that I could be barking up the wrong tree. I guess that it could be a mechanical or hydraulic problem.

Other than this issue, the transmission performs as well as the day I purchased the vehicle. Last month, I drove 900 miles in one day to pick up a 3000-lb. travel trailer and returned towing it on a 1200-mile, three-day route without an incident. Two weeks later, I pulled the same trailer to the mountains (120 miles, the first 80 miles on the interstate and the last two included a paved 25% grade up to the campground). We rode several dozen miles on some forest service and mountain roads of varying condition (w/o the camper, of course), and then pulled the camper back home. The problem never occurred until I was approximately 40 miles from the end of the trip. I have not experienced the problem since then during daily driving.

1. Can you recommend any other testing procedure not listed in the FSM or "AW4 Jeep Diagnoses" by Wayne Colonna that could help me determine the faulty component?
2. Can I back-probe the wiring harness connector at the TCM with a VOM while the TCM is plugged in, the engine is running, the vehicle is moving, and the problem is occurring without causing damage to the components being tested?
3. Do you think that it would be of any benefit to hire a professional who has the equipment required to interface with the TCM memory to retrieve diagnostic trouble codes and/or to perform any other checks such as pressure testing?
4. Is it harmful to the transmission or torque converter (clutch) to allow this condition to continue? If so and if I can not find the source of the problem whether it is electrical, hydraulic, or mechanical, would you recommend that I disconnect the TCC solenoid and operate the transmission without lockup? I have read somewhere (possibly here) that placing a switch in the TCC circuit and controlling lockup myself may result in damage if I were to leave the clutch locked at the wrong times such as in reverse or high-torque situations. Is that true?
5. Do you have any "educated guess" as to what may be my transmission's fault?

Thanks for any assistance that you can provide.

 

[kastein]

Sounds like you have a pretty good grasp of what's going on and what you need to do. I suspect you are right about the intermittents, they are my least favorite issue to track down for exactly that reason. They NEVER fail when I've got my electrical test equipment with me...

It might put somewhat more wear on the torque converter clutch, but I wouldn't worry about it too much, especially if it's happening at fairly low throttle conditions cruising on the highway. If you override it and leave it locked while in 1/2/R gears, yes, it can definitely cause damage, and will make the vehicle respond badly and shudder anyways, so I don't recommend people do that.

My guess is that you're right about the TQ lockup solenoid or hydraulic circuit being the issue, BUT it could also be a slipping clutch for one of the other gears or a hydraulic pressure issue. I'm sure you'd have something like unexplained overheating issues (slipping auto trans is the easiest way I know of to pump a massive amount of heat into the coolant without any engine symptoms) or driveability problems if it was anything other than the torque converter lockup however.

You can backprobe anything you want without any damage, just make sure to use the voltage scale on your meter, using the resistance scale may damage the meter and won't tell you anything anyways in this case. I'd actually recommend an analog meter for this, intermittents are much easier to catch when you can see the needle start jumping around out of the corner of your eye while driving instead of a constantly but slowly updating digital readout.

Basically anything intermittent in the circuitry and hydraulics that control the torque converter lockup can cause this. Things to suspect: dirty contacts on the brake light switch or an intermittent torque converter lockup solenoid. It MIGHT even be a marginal solenoid driver transistor in the TCU, but that's less likely than the other two things I listed.

 

[HappyDog]

Have you checked the connectors next to the transmission fluid dipstick? Sometimes those contacts get corroded or dirty, or the wires get manhandled and broken so sometimes they touch and make contact, then vibration causes them to lose contact again.

I would be tempted to wire in two 12v lights or LEDs -- connect one to the TCC contact on the TCU and the other to the TCC contact on the connector on the transmission. If the one connected to the TCU stays lit while the one connected to the transmission flickers off, you know it's a wiring issue between the two. If both stay solidly lit while the TCC slips on and off, the problem is inside the transmission -- failing solenoid, etc.

 

[XJjamez]

Ok guys, I'm back on the XJ. Tomorrow is tranny/tranzaxil drop day. I was mistaken as to what plug was the OSS, but I finally did find it on the tranny. Pulled the sensor and felt for posts on the rotor. Sure enough four posts. The parts houses dont have the single ping rotor. My question for the evening is; think I can just grind down three of the posts and the rotor NOT fly apart at interstate speeds?

 

[XJjamez]

I know how you guys love pics, I know I do. So here we go;

This is big beastie Betsy

This is her proper name

This is what I've done to her, now it is a single pulse/rev to accommodate the 1996 tcu. Dont know if it'll work so I wouldn't try it....yet.

And finally these are the three wires that I was wrong about being to the OSS (thanks guys). I now believe that it is to the VSS, if that is the sensor that is located at the rear most of the transfer case. Any way the wiring code changes at this plug. Was wondering which ones were suppose to connect up. On the down side of today, found out I have a bad NSS. Checked it with the ole fluke and only had continuity at the proper pins in the drive position. Great, and those aint cheap. Also did not burn the front seal but rather the bearing behind it pushed it out. looked like if had a few screwdriver gouges in it, so probably should replace it too.