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Thread: 99 Jeep Grand Cherokee Limited, 4.7L 4WD Tranny

  1. #1
    Senior Member DonTom's Avatar
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    99 Jeep Grand Cherokee Limited, 4.7L 4WD Tranny

    This is mainly for info. only, I don't have any questions, but any comments are more than welcome.

    In my 99 Jeep Grand Cherokee Limited, 4.7L 4WD Tranny, I got a OBD2 MIL code of P0731 four days in a row, (I erased the code each day). Also, sometimes, when I come to a stop, there is a jerk. Sometimes barely noticeable, other times we would almost go through the windshield if it were not for the seat belts. It happens when coming to a stop, very slow, at perhaps 8 MPH or so.

    This Jeep has 190,000 miles on it. But I plan on keeping it for quite a while.

    My understanding is these Jeep 4WD trannys should NOT shift down to first gear until there's a full stop. But it seems it is shifting down often, and quite violently, just below 10 MPH.

    I took the Jeep to an auto tranny shop yesterday and they could NOT verify any problem in doing a test drive. Also, I already erased the MIL code of P0731. It seemed this tranny shop didn't want my business unless they could verify a problem. They even want to see the P0731 for themselves. Anyway, while they had this Jeep up on the rack they noticed the front differential had a bad leak. Just last week I spent a couple of thousand bucks having the entire driveline stuff replaced because it made a lot of noise. Seems one of the new seals leaked that they replaced in the front differential.

    So I drove the Jeep a few miles down to the DriveLine and Gear Service shop in Reno. On the way there, of the 12 times I had to slow down for a stop, it had the severe jerk problem 8 times at just under 10 MPH.

    So today they call me and tell me they fixed the bad seal problem. I pick up the Jeep and drive it home and there was no trace of the deceleration jerk all they way home. But just before I got home, the check engine light went on again. I left my OBD2 reader at my other home here in Reno, but I do assume it's the same P0731 again. I will know for sure tomorrow.

    Another thing I wanted to mention . . .At this automatic tranny shop, I got in a chat about trannys with the owner. He said that it is best , in his opinion, that trannys are never flushed. He says when they are fully flushed, often the garbage in the ATF moves and gets stuck in places that can cause serious problems. He says the old simple way of just doing a tranny filter change with a couple of quarts of new ATF is a much safer and more reliable method. Anybody else here heard this before?

    But he also said my Jeep looked very well maintained and that my ATF still looked like new. I have not had this jeep long, I bought it used recently, but I found out the previous owner was a multimillionaire, John Ascuaga. This was discovered at a Jeep dealer here in Reno after I purchased it, when I went to buy a small part that required the Vin number. John is now probably too old to drive. He is now around 90 years old. But still looks well. I have seen him recently walk through the Nugget casino, which he recently sold.

    -Don- Reno, NV

  2. #2
    Administrator Ken's Avatar
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    Hi, Don.

    Possible causes

    - Low transmission fluid level
    - Dirty transmission fluid
    - Shift solenoids
    - Transmission mechanical problems
    - Transmission hydraulic control circuit

    P0731 Jeep Description
    This diagnosis monitors actual gear position by checking the torque converter slip ratio calculated by Transmission Control Module (TCM) as follows:
    Torque converter slip ratio = A x C/B
    A: Output shaft revolution signal from revolution sensor
    B: Engine speed signal from Engine Control Module (ECM)
    C: Gear ratio determined as gear position which TCM supposes
    If the actual gear position is higher than the position (1st) supposed by TCM, the slip ratio will be more than normal. In case the ratio exceeds the specified value, TCM judges this diagnosis malfunction.

    If you have had the drive train replaced then some of the above can be ruled out - e.g dirty tranny fluid. Low fluid, if your leak was really bad could have been the problem. Otherwise it could be a solenoid or hydraulics problem - if the solenoid pack is external to the tranny and the shop refitted the original pack that could be one check to get done.

    My guess is that the shop that replaced the drive train need to give it a thorough check out for you.

    Ken.


    Die dulci fruimini!
    Ken.
    Wolds Bikers, Lincolnshire, England.

  3. #3
    Senior Member DonTom's Avatar
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    Quote Originally Posted by Ken View Post
    If you have had the drive train replaced then some of the above can be ruled out - e.g dirty tranny fluid. Low fluid, if your leak was really bad could have been the problem. Otherwise it could be a solenoid or hydraulics problem - if the solenoid pack is external to the tranny and the shop refitted the original pack that could be one check to get done.

    My guess is that the shop that replaced the drive train need to give it a thorough check out for you.

    Ken.
    Come to think about it, never felt the jerk nor got the PO731 before the drive line stuff was replaced.

    Anyway, I went to check the OBD2 code today and to my surprise, this time it is NOT a P0731. This time, it's a P0715.

    I will now keep this OBD2 tester in this Jeep for a while.

    The Jeeps seems to drive fine, so I decided just to erase this code, drive it a few more weeks, before making any decisions on having it fixed.

    Until the next check engine light . . . .

    -Don- Reno, NV

  4. #4
    Administrator Ken's Avatar
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    Hi, Don.

    "P0715 - Input/Turbine Speed Sensor Circuit Malfunction"

    As you say - 'Until the next check engine light.' is probably the best bet.

    Ken.
    Die dulci fruimini!
    Ken.
    Wolds Bikers, Lincolnshire, England.

  5. #5
    Senior Member DonTom's Avatar
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    Quote Originally Posted by Ken View Post
    Hi, Don.

    "P0715 - Input/Turbine Speed Sensor Circuit Malfunction"

    As you say - 'Until the next check engine light.' is probably the best bet.

    Ken.
    Here's the good news . . . I got the P0715 again. So I removed the input speed sensor from the tranny and checked the resistance. It measured infinite, proving this speed sensor wasn't doing anything at all. So yesterday I bought a new one at the local auto parts store. They had it in stock for just $20.00 (15.00?). When I got home, I measured the resistance of this new one, using the same ohmmeter, and it measured 500 ohms, which sounds good to me.

    So I installed it and the car now feels like new. I cannot even tell when it shifts, as it is so smooth, unless I check the tach. There's no doubt it is fixed now. All those weird tranny problems were caused by a bad tranny input speed sensor. It was very easy to replace, only took a few minutes.

    It also makes sense how I got the OBD2 code that first gear was the wrong ratio. It uses the speed sensor on the input and compares it to the output sensor. If the sensor has a problem, it can give me wrong info. and set a related, but incorrect code. I assume I had an intermittent speed sensor that finally crapped out completely, and set the 715 code.

    -Don- Reno, NV

  6. #6
    Administrator Ken's Avatar
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    'Sorted' as we say over here. Hopefully there will be no more tranny problems for a few years - happy motoring, Don.

    Ken.
    Die dulci fruimini!
    Ken.
    Wolds Bikers, Lincolnshire, England.

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