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Discussion Starter #1
So I bought this Jeep a few weeks ago knowing it had problems, but sometimes ya gotta drive what you gotta drive.

A quick trip on the highway tells me the overdrive is not even trying to engage. The light above the o/d on/off button is lit and will not go out no matter how many times I press it. The trans fluid is full though slightly off color. It's not burnt by any means, it's just a few shades darker than fresh fluid. Would this be an electrical issue? There are a few scattered issues with other electrics though nothing even remotely of this caliber.
 

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Welcome to Allpar. 6 or 8 cylinder? The PCM controls the torque converter clutch lock-up, the electronic governor (if equipped) and the 3-4 shift. 4th being OD. Something may be keeping OD locked out.
Any 'ck eng' light on or fault codes? http://www.allpar.com/fix/codes.html
Diagnose first. A road test with an OBD I scan tool may show what the PCM is or isn't seeing to allow OD or it could be an internal transmission issue.
 

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Discussion Starter #3
Sorry, I guess a bit more info would be helpful.

The Jeep has the 4.0 straight six with the full-time 4wd transfer case. The only warning light, other than the ABS, is the little amber light above the OD on/off button. No amount of playing with this button will shut the light off. There are a few electrical issues that i know of. The speedo works when it wants to, the rear wiper is non-responsive, and if i don't pull the stalk all the way when switching the high-beams the lights shut off. Pulling the stalk all the way will turn them back on. The light issue only happened once, but that was enough for me to remember to pull until I hear the click. The cruise control works great though, lol. Also the radio is dead but I'm pretty certain it's just age on the stock head unit.

I don't have access to a scan tool and really don't have the funds to acquire one. Can I pull the codes with the old off-on Chrysler trick?
 

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A 95 4.0L would have a separate TCM to control the transmission functions. I believe the same key trick will work to pull codes, but you have to watch the blinking of the OD light. There might also be a trick involved, like holding the OD button while you turn the key on and off. The TCM codes are different from the PCM codes.

Several electrical things could keep the OD from engaging. The OD solenoid could have a short or open, or the transmission fluid could be reading too hot due to a bad temp sensor.
 

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I thought that by 1995 the Aisan-Warner AW-4 was Cherokee (XJ) only and that the Grand Cherokee (ZJ) would have been a 42RE?
The Aisan-Warner had a separate TCM and the 42RE used PCM electronics. Do you have the last 8 of the VIN handy?
 

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Check the fault codes first. These are general fault codes, not specific to the transmission, which stores its own fault codes in the TCM. You do not need a scan tool to do this. Please report back what you find.

http://www.allpar.com/fix/codes/index.html

Several things will cause overdrive not to engage:

1) Faulty on/off switch. However, this is supposed to release the OFF setting when you shut the vehicle off, and reset to the default ON.
2) Vehicle's coolant or transmission fluid is too hot or too cold, or computer thinks that it is. Up til about 1992, input from the coolant temperature sensor is used. Sometime around 1993 or later, there is a transmission fluid temp sensor inline in the cooling lines, used to judge whether to shift to O/D and whether to lockup the torque converter. Too high or low a reading will prevent the shift.
3) Transmission fluid too low, or contaminated.
4) Faulty solenoid inside the transmission.
5) LOOSE solenoid inside the transmission. In my case, the solenoid pack is screwed to the side of the valve body inside the pan, and there is a gasket and a mesh screen between the two. The screws loosened up so that the solenoid pack was not sealed to the valve body, causing a hydraulic leak around the path, and this prevented O/D and prevented lockup release.
6) Thermostat not opening fully.
 

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1993-1995 4.0l Grand Cherokees (ZJ) had a TCM for the 42RE. In 96 control was incorporated into the PCM. Also, on this design the transmission temp sensor is either attached to the solenoids, or build into the governor pressure sensor transducer (if it has 4 wires. if it has 3, it's separate)
 

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Discussion Starter #8
So sorry I took so long coming back to this thread. My laptop decided to take a dump on me and I just now got it repaired.

So I tried the Chrysler key trick but only got the pcm codes. One was for a recently disconnected battery, and the other was for the engine coolant not reaching 170. Considering the Jeep currently has no thermostat this doesn't surprise me.

How in the world do I get the codes out of the tcm so I can figure out what it's problem is?
 

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You will likely need an advanced scanner to read the transmission codes.

However, before spending any money to have that done, consider that OD is locked out until a certain temperature is reached. I doubt the lack of thermostat is keeping it that cold, but I'd put a 195º thermostat in it and see how the transmission behaves.
 
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