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NEED HELP WITH JEEP OVERDRIVE!!!!!

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  • #662182
    kylekyle
    Participant

      I have a 1996 jeep Grand Cherokee 4.0 2wd. ever since we bought the jeep with 78,000 miles on it the over drive button has never worked on it. it now has 221,000 on it, when you turn the jeep on the light comes on for a split second and goes away. when the car is running and u click the button it does nothing, so its stuck in overdrive pretty much… i changed the relay under the hood and did nothing. i was woindering if there was a way to test it by connecting wires behind the module or something. this has been bugging me for ever. why isnt my overdrive button clicking on. it lights up for one second when i turn the jeep on and then it shuts off, so when i click it, it doesnt light up or do anything. the rear wiper button and rear defroster button work and its on the same module.trans fluid is at normal level and looks ok. also i have changed several modules out to see if it was that… its not lol PLZZZ HELPPP :ohmy: :ohmy: :ohmy: :ohmy:

    Viewing 15 replies - 1 through 15 (of 19 total)
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    • #662212
      college mancollege man
      Moderator

        See if this helps. I would like to suggest either having any codes read or see if you can pull
        the codes and post them to help further the diagnoses.

        http://www.nagca.com/forum/showthread.php?t=23957

        #662214
        kylekyle
        Participant

          the only engine codes i get are 12 21 and 55 which ik 21 is an oxygen sensor but im sure that has nothing to do with it. ive been told i can turn the key so many times to get a tranny code check. but i think my jeep only checks engine codes not tranny. to my knowledge they r separate right? also my problem is that its not clicking out of overdrive its stuck IN overdrive

          #662331
          Nick WarnerNick Warner
          Participant

            That should have a separate trans control module. To get the codes and view data you need a higher-end scanner that can access it. For the age of your vehicle, even an old SnapOn red brick would be able to get the codes and data that you need.

            Are you towing something with this? I’m wondering why you are trying to disable the overdrive, as the only reason you would need to do so is if you are towing above a weight limit given in the owner’s manual. Its not like it is “stuck” in overdrive, it is simply able to shift into it when the TCM and PCM believe it should be in overdrive based on the parameters it reads at the time. The reason you would disable it is when you are towing a heavier load and would not want to cause the excess heat in the trans that overdrive would create. Same idea as on a manual tranny not shifting past 4th gear. Then you have direct drive (1:1 ratio) which doesn’t put the engine at a mechanical disadvantage.

            If you are having other symptoms indicating a fault in the trans, that would be something else to diagnose. Again, you would need a scan tool capable of reading data and performing ATM tests in the trans along with a master pressure gauge/ adapter set to measure line pressures at the given ports to truly nail down what is causing the issue.

            #662369
            college mancollege man
            Moderator

              see if this helps you further. follow the procedure.

              http://www.jeepforum.com/forum/f13/95-zj-diagnostic-codes-629996/

              #662395
              kylekyle
              Participant

                i like to pop overdrive out around town for when i need quick speed. i forgot to tell you guys. last week i was driving the jeep and the alternator failed on me and the battery got so low on the way home that the windows wouldnt even worked. i did notice my overdrive was kicked out and the button was lighting up green but when i hit the button it stayed out of overdrive and still didnt work. idk if that helps toward the problem but i just find that way to odd. mybe the battery didnt have just enough juice to keep the overdrive on. thanks

                #662457
                kylekyle
                Participant

                  erik the car guy.. ik u know whats up!

                  #662739
                  Andrew PhillipsAndrew Phillips
                  Participant

                    [quote=”96grndcherokee” post=135194]i did notice my overdrive was kicked out and the button was lighting up green but when i hit the button it stayed out of overdrive and still didnt work.[/quote]

                    There are three possible situations in my mind. The switch is bad (or connected poorly), the wiring between the switch and PCM (computer) is damaged, or the PCM has a bad driver for that circuit.

                    First, rule out the switch. Remove the dash cover(s) until the switch is exposed. Disconnect the switch at its connector, inspect it for corrosion or damage, and if it looks good, re-connect it and test the switch. With the key on and engine not running, the light should go on/off when the position of the switch changes. If it still doesn’t work, disconnect the switch again, and use an ohmmeter across the terminals on the switch itself. When the switch is closed, you should get a reading of 0 ohms, or fairly close, and infinite when the switch is open. If the ohmmeter shows 0 or infinite regardless of the position of the switch, the switch is bad. If the switch tests good then you can rule it out and we are left with the other two possibilities. Leave the switch disconnected for now, because we will need to access the connector during the next part.

                    Next, locate the PCM. It is usually mounted to the firewall behind the coolant reservoir. There are three large harness connectors plugged into it (grey, black, and white colored). Once you have found the PCM, you want to locate connector “C” (the black one) and carefully unplug it. Pins C6 (brown wire with yellow stripe) and C13 (orange) go to the overdrive switch. With an ohmmeter, on the connector (not the PCM), read across these two terminals. Because the switch is disconnected inside the cab the meter should read open/infinite. If you get any kind of reading other than infinite, there is a wiring fault. Otherwise the next step is to use a paperclip or short piece of wire to short the terminals of the switch connector that you left loose. Those should be brown/yellow and orange. Now when reading across the brn/yel and orange wires on the PCM connector, the ohmmeter should read zero, or fairly close. If it still reads open, there is a wiring fault between the switch connector and the PCM. If the ohmmeter displays zero with the connector shorted, the wiring is good and can be ruled out, leaving the driver circuit in the PCM as faulty, in which case the fix is to replace the PCM. Don’t forget to plug the harness connector back into the PCM.

                    #662820
                    kylekyle
                    Participant

                      thank you. i will check the pcm when i get the chance tomorrow, it might be the wiring. the pcm has been changed 3 time within its life time and the overdrive button never worked.. also i have replaced the switch multiple time just in case i got a defect. also when i turn the key that button lights up for a split second so there is power going to it and ik the connection it there i just cant figure out why it doesnt want to kick out of overdrive

                      #662822
                      Andrew PhillipsAndrew Phillips
                      Participant

                        The brown/yellow and orange wires go straight from the PCM to the OD switch. The PCM ‘reads’ whether the switch is on or off and then controls the transmission accordingly via commanding a solenoid on and off. There is nothing else on that circuit. If the switch is good, the wiring is good, and the PCM is good, then it should be working. Even if there were a problem with the trans solenoid, the dash light would still come on and off when the switch is pressed, because it is software controlled. You could remove the trans completely and the light would still go on and off when the switch is moved.

                        You say the PCM has been changed several times and the light comes on for a second when starting and then goes off. That really sounds like a PCM/software issue. Why were the previous PCMs changed? Also, with Jeeps specifically since the PCM contains the TCM (transmission control module), it is essential that the correct PCM software is used. There were several different vehicle models with different options (i.e. fed vs cali emissions, trans equipped with the mode switch (power/comfort), the police package, and several other variants). If the PCM installed doesn’t have the correct programming for the options your vehicle has it can cause things to not work, work improperly, or even cause the PCM to fail.

                        #662887
                        kylekyle
                        Participant

                          why would it just blink at me once at initial start up? and also work when my battery got so low on charge it kicked it out, that tells me that the jeep is capable of kicking out it just doesnt want to for some reason? maybe solenoid in the tranny??

                          #662913
                          Andrew PhillipsAndrew Phillips
                          Participant

                            [quote=”96grndcherokee” post=135684]why would it just blink at me once at initial start up? and also work when my battery got so low on charge it kicked it out, that tells me that the jeep is capable of kicking out it just doesnt want to for some reason? maybe solenoid in the tranny??[/quote]

                            I can currently rule out the trans solenoid being the source of the switch/light problem, because the switch and light operation is independent of the trans and solenoid operation. The trans and solenoid (which is on the trans) don’t even have to be installed and the switch/light would still work. If the light was coming on and off with the switch and *then* OD wasn’t working, the solenoid might be suspect. In this case, even though the solenoid might be bad (we don’t know, because the switch isn’t working), that isn’t the issue we are currently troubleshooting.

                            The OD light is software controlled, not mechanically controlled. It comes on and off when the computer commands it to. The computer is supposed to command it on when the switch is closed and command it off when the switch is open. When the light comes on and off without the switch being operated, that is a computer/software problem, or there is a wiring fault, or a random short that may be causing the computer to react as if the switch were being operated.

                            When the battery voltage drops very low that causes all sorts of glitches in the computer on any vehicle. The computer has one or more internal voltage regulators that takes the battery voltage and regulates it down to 5v. When the voltage on the battery drops too low (below 10v), the computer’s regulator can no longer provide that 5v any more (it can actually be as low as 1v or even drop to zero), and that causes random things to happen, such as indicator lights coming on, spark misfires, trans not shifting, even engine stalling. Bad batteries or failing alternators can also cause under/overvoltages or inject alternating currents that can cause similar malfunctions.

                            Let me digress a little bit. What is the PCM? It is a circuit board that contains a set of digital and analog inputs that the switches and sensors connect to; a set of digital outputs that the indicator lights, relays, and solenoids connect to; a memory chip and a microcontroller. The microcontroller runs a program (firmware) that identifies what each input and output are for and how to control the outputs based on the conditions of those inputs. For simplicity’s sake, let’s consider this scenario: Jeep A and Jeep B are the same model and year, but were built with different options at the factory. On Jeep A the transmission has electrically controlled shift points but Jeep B has mechanically controlled shift points. Jeep A has a switch on the dash marked Power and Comfort. This switch causes the computer to command the shift points for the transmission differently based on its position. Jeep B has a switch marked Overdrive Off instead. But, it’s connected to the same ports on the PCM as the Power/Comfort switch on the other Jeep. The PCMs themselves are physically and functionally identical, but the software inside them is what is different, so that the transmissions operate properly. If you were to switch the PCMs between these two vehicles, they would still start, run, and drive, but the functions of that input would cause different operational results in the output, or do nothing at all. In most cases, if the PCM is in proper functional condition, it can be reprogrammed with the correct software version for the vehicle it is installed into.

                            I am not saying that this is actually what is happening on your vehicle, it is meant as an illustration scenario to show how same-model variants could be affected by PCM software differences. But, what is happening on your vehicle may be very similar to what I just described. You already know that the current PCM is not original. You also know that the previous PCMs were not original equipment. Without knowing that the software in the PCM is the correct version for your vehicle with its equipped options, you cannot be sure that it is operating your vehicle correctly. You never did answer my question why the PCMs were changed out before. That detail could be a clue.

                            #662929
                            kylekyle
                            Participant

                              they just gave up on us so we had to replace them. i believe we did buy the right one for the jeep so idk if it would be that, but theres always a chance of that happening. ill take the module out and look for the brown and yellow striped wires and see what i can do. wht if i have different colors? also when the jeep had its original pcm the overdrive still didnt work lol like when the day we bought it. i appreciate the input btw

                              #662933
                              Andrew PhillipsAndrew Phillips
                              Participant

                                If it didn’t work even with the factory original PCM then I would suspect a wiring issue. However that doesn’t explain the light blinking on for a second at startup. (EDIT: I just checked on this, and there is a self-test that causes this light to blink for a second when the engine starts. So, that operation is normal, but still doesn’t rule out a wiring issue with the switch.)

                                Make sure the wiring in the switch connector itself is good and a wire hasn’t broken off inside the connector. The ohmmeter test I previously laid out should definitely help. The colors should be the same. Look at the C connector on the PCM first and find the 6th and 13th pin, or look at the OD switch connector. If they are different colors than I mentioned, then use those colors instead, but they should be as I listed. As an aside, check fuse #17 in the under-hood fuse box. It powers the trans solenoid. That won’t solve the switch problem, but will make sure the solenoid is powered when the switch issue is solved.

                                #662935
                                kylekyle
                                Participant

                                  ok when i take it apart today i will pose pictures of what it looks like under it so u can see

                                  #663120
                                  kylekyle
                                  Participant

                                    i do have the wires u are talking abut and tested the pins on them and got zero resistance so is that what i am supposed to get or not?

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