99 Jeep Grand Cherokee-overdrive issue

BadBob67

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We have a 99 Jeep Grand Cherokee Laredo 4.0l Auto with OD.
Transmission fluid is correct level and has been changed within the last 3 weeks.
We are having an issue where after the car warms up it will not shift into overdrive, it shifts in when cold but after tranny warms up (about 10 min) it wont shift into overdrive.
Need ideas on where to look. Thinking a relay? a resistor? or a ground?
Problem was there before the transmission fluid was changed.
 

kev2

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First have the vehicle scanned for codes. ESP those so calle d MANUFACTURER specific P1xxx and up
Are you sure it is OD and NOT TCC?

PS: jeep requires a specific trans fluid - did you use it?
 

BadBob67

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Transmission fluid was replaced by a dealer, so its the correct fluid.

As for the OD or TCC I am not sure, the shifter has a button that says OD but I never touch it. When the vehicle is cold it transfer fine, after about 10 minutes it stops shifting up. How would I find out which one it is?

The only code we get is an O2 sensor, which we will replace this weekend.
 

kev2

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The fluid was changed by dealer - did you mention this no OD issue to them? Was the thought that fluid would correct no OD what did they advise? Something is missing.

Did you scan the vehicle? the codes for a trans issue may NOT show up doing thr key "dance" or when using DIYer code readers.

I will try to post a DIYer no scanner suggestion- Later after coffee -

PS - post the code for o2 - remember a code NEVER states change part...
 

billr

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Well, if you have an emissions code, get that resolved before worrying about the trans. That code alone could be the cause of odd shifting. Unfortunately, not all dealers, or their personnel, are knowledgeable about the products they represent; and likewise, not all are as diligent or ethical as we would hope. Point is, you can't just assume they used the correct fluid; it's best to ask and get the brand/type listed on the service order.
 

kev2

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here is an easy plan-
1) get a scan - FREE at autozone, advance, Orielys et al- its free!
2) start vehicle to drive for your free scan- depress OD switch - the overdrive light in instrument panel .... will come on... YES OR NO?
3) drive vehicle you should feel shifts 1-2 2-3 .... watch tach, as the TCC locks up you should see an .....RPM decrease indicating that the lockup happened... yes or no.

POst all codes and answers to 2 and 3
 

BadBob67

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PO138 is the error code I get from my reader.
Mopar® ATF+4 was used by the dealer I checked the invoice.
The fluid was changed because I had 110,000 miles and figured it was time. No issues other then the OD not working but fluid wasn't changed for that reason.
also have an issue with the radio and shifter lights going on and off....could this be a ground issue?
can see it go from1-2, 2-3 on the tach but once at 3 tach goes up and never shifts down and no OD light never comes up on the instrument panel.
 

kev2

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>> With vehicle running - Did you depress the the OD button on shifter?
this should cause the OD light to illuminate-
>> When eng cold - that 10minutes you spoke of - do you notice the shift 3-4, only to have it stop shifting 3-4 as it warms past that 10min...
>> OK make sure your code reader will display MANUFACTURERS SPECIFIC codes, P1xxx and up - might check theor web site...
 

kev2

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We will need to check th OD switch- be sure it is working, not grounded, and check to see if the PCM is energizing the 3-4 solenoid... the problem is how without a scanner.... I am currently thinking of a way to easily confirm this...

the OD needs to be on - default mode- the circuit NOT grounded, then the PCM energizes the 3-4 solenoid IF conditions are correct- If the PCM energizes the circuit and still no OD the issue is trans internal. IF no voltage on circuit PCM is suspect.

Ideally the scanner will tell us all this- OD mode on or off, if PCM energized 3-4 solenoid...
 

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NickD

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On GM and Ford vehicles, one tap on the brake pedal will disengage the TC lockup. If that brake switch is not making contact, lockup will never engage. Can be loose or just have dirty contacts. Wonder if Chrysler is the same?

Also had problems with a dirty neutral safety switch, more than just a neutral safety switch, whole bunch of AT solenoid wires go through these things. Torque converter lockup is just one solenoid valve when opened applies hydraulic pressure to the lock up clutch. To open hit, has to be hit with 12V and can be locked up all the time if that 12V is always present. Just the opposite problem as no torque converter lockup.

Having a circuit diagram sure helps and a VOM. Ha, not a problem with a manual transmission, all gears have torque converter lockup, to release it, just step on the clutch. To put them in OD, have to shift the gear lever do this do. With an AT, this is done for you, if all is correct, both mechanically and electrically. Another cause could be a defective torque converter solenoid, can hear it click and do a current test, with the ignition off and the harness disconnected by hitting it with 12V.
 

BadBob67

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ok I went to the dealer to ask them a question about this and a mechanic was nice enough to tell me it sounds like a defective tcm, he told me to check the tcm for damamge or shorts.....anyone know where to locate the TCM on a 99 Jeep Grand Cherokee Laredo 6 cyl 4.0l straigt6?
 

kev2

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I will dbl check but I think separate TCM (Trans Control Module) was only with the 45RFE trans their 8 cylinder combination.

hopefully BP has this stored in memory
 

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Jamie

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I have this exact same problem. Same car, transmission, engine, symptoms, and even same code. I was shocked to see how much it was the same. I mean every symptom she said, its like she was driving my jeep. Someone please tell me what fixed it. I have been researching TCM all day and can't seem to find one on my jeep. Perhaps they combined this function with the PCM which I have located. Doing more research I have found that the PCM also controls idol ( have intermittent idle problems also on startup only ), AC clutch control (that doesn't work either ), speed control ( no cruise control for me), transmission features ( obviously got O/D problem right) and I forgot the rest it does but seems a lot matches up... any advice for me guys.

1999 Jeep Cherokee Loredo inline 6 4.0L ...
 

kev2

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jamie - start a NEW TOPIC- tell us - is vehicle stock? exactly what codes are you seeing- Take for a free scan autozone, advance. orielys parts stores do theem for free get codes and post with any other issues
 
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