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Jeep Grand Cherokee PCM Module Replacement

24

Comments

  • steverstever Guest Posts: 52,454
    If you paid with a credit card, you could dispute the bill. Then if the credit card company doesn't back you up, you could take the dealer to small claims court.

    First thing to do is talk to the service writer about a refund, and if that doesn't work, send a letter to the owner. Then you have some documentation to attach to your credit card or small claims dispute.

    Your local consumer protection agency may be able to go to bat for you too.
  • godawgs1godawgs1 Member Posts: 1
    Did you ever fix the problem? I have a 2001 Cherokee sport with the same problem. Can't afford to get ripped off by dealership
  • bill24060bill24060 Member Posts: 4
    The problem I had doesn't sound like the one you had. I took the jeep to the dealer and they said I had a small leak in the valve cover that was allowing oil to get through a break in the manifold gasket and was getting on a sensor in the exhaust. Anyway they fix it perfect at a price of $850.00. If I knew what was wrong I could of fix for around $20.00. good luck
  • jeffwtuttlejeffwtuttle Member Posts: 15
    Mr.C
    Yes I did fix the problem and it was a simple coil problem! Thanks to all the help out here And as far as getting my money back it was a waste of time talking to the dealership and the BBB. I got no where with it? Any Ideas?
  • pla4kpspla4kps Member Posts: 10
    i am interested in hearing more of what you did to your jeep if you dont mind . im having major problems with mine. i dont have spark. so far i have tested and replaced the batt, the coil, the crank sensor, the cam sensor ( aka the sync signal generator inside the distributor ) and have tested power at the coil. i am getting power at the green / orange wire . when i flip the test light to + i am getting ground at the coil but not while cranking. i have tested the wire from the pcm to the coil and it isnt broken or damaged. the truck sat in an impound for 2 1/2 years before i bought it. it took close to an hour to get it jumped and running and even still i had to keep my foot on the gas at all times or it would stall. can the pcm lose its memory?? does it have to be reflashed?? is their anyway to do it myself?? i am posting this on every message board i can find so if you like you can reply to me directly at rubbercitypits@gmail.com thanks everyone for your help.
  • barnaby95barnaby95 Member Posts: 10
    If you have ground that disappears while cranking the engine, check the ground from the battery to the body and to the engine. I ran a ground strap from my block to the body and it cleared up a lot of intermittent "ghost" problems. Also, I would replace the plug wires, if you haven't already. They do lose conductivity over time and can affect the strength of the spark or kill it altogether.
    If you have to keep your foot on the gas to keep it running, it sounds like the throttle position sensor is bad. It is located on top of the engine on the intake next to the butterfly valve. I would recommend replacing that first. The part is about $45.00 at autozone and takes about 15 minutes to replace. You will need a torx driver to get the screws out. About a 20 or the next size larger.
    There is another small unit mounted right behind it. That is the idle air control valve. It's about the same price. Takes about as long to replace. If you choose to replace that too, get a can of spray carb cleaner and spray it into the hole under it. This will clean out any oil or dirt that may have deposited there, preventing any continuation of your problem.
  • gregjatkinsongregjatkinson Member Posts: 22
    i have a 93 5.2 grand cherokee that will not start at the ignition but it will start at the starter relay with the key on and the fuel pump relay out. put the fuel relay in and it kills the engine. but with the key on fuel relay seems to work fine till you try to start it-it doesnt spark. i cant get nothin to work through the ignition only at the starter relay. my fuel relay feeds my fuel pump and oxy sensor they both seem to be fine. the problem originated with blowing my engine fuse once put new one in ran fine for a while blew again put new one in wont fire found a bad short on b+ to coil fixed the short and still nothing. on this jeep the autoshut down relay and fuel relay coils run off the same power & ground circuits. thought the items they are feeding b+ comes from diferent fuses. could the short off of my asd relay backfeed through to my fuel relay and pcm.
  • gregjatkinsongregjatkinson Member Posts: 22
    try turning the key to on position pull the fuel relayout of the pdc (fusebox), pull the casing off starter relay, make the starter relay connect by pushing the contact and see if it starts that way if so i have the same problem been working on for a month
  • Jaweh999Jaweh999 Member Posts: 9
    Has this issue been resolved? My issue sounds similar. I have a 95 JGC, 2WD, Auto, 4.0. I have replaced the PCM (twice), the CPS (from Mopar), Ignition Coil, TPS. Here is the deal.

    Step 1) When I turn my key to the "on" position the fuel & auto shutdown relays chatters and the Check Engine light does not come on (even temporarily). The fuel pump does not prime when I just turn the key on, however, when I crank the engine over and I get fuel pressure to the fuel rail (approx 40lbs).

    Step 2) IF I PULL the fuel relay and turn the key "on" without cranking I get the Check Engine light for a few seconds and the fuel pump will not prime. If I crank the engine over without the fuel relay the engine starts but dies shortly after starting because the fuel rail no longer has pressure. Remember it had presssure in step 1.

    Step 3) I just don't have a clue where to go..I have replace relays, etc.
  • gregjatkinsongregjatkinson Member Posts: 22
    have you checked out your oxy sensor at all sounds the same as my problem mine

    step 1- turn key on; fuel pump fires up I get pressure everything seems fine at this point

    step 2- try to start the jeep; with fuel relay in it just cranks- pull relay fires up runs for a second no fuel of course

    step 3- with engine running I put fuel relay in it kills it out

    Mine seems to be a short either on oxy sensor or a signal to the pcm from one of the various sensors i have made sure my fuel pump is good
    what i am going to try is go back through testing my sensors but doing it at the pcm instead of at the sensor location

    For some reason it seems like that fuel relay is causing the problem only once you try to start the vehicle has to haave something to do with a signal to the pcm during start mode

    I have a spot that you can get all the factory info for your jeep (scribd) has diagrams for wiring also has papers on how the pcm works during different modes
  • gregjatkinsongregjatkinson Member Posts: 22
    I just got doing testing voltage on my auto shutdown relay and fuel relay. I know the power side of my relay and the ground side on the electro magnetic coil. with the asd relay out and fuel relay in (both work off same power and ground circuits) my voltage is showing correct on the ground side (with my neg lead off of meter in the ground side of relay and pos lead from meter on battery power) showing 12 volts but when I put my asd relay in and pull fuel relay its testing through the fuel relay holes that i have to put pos lead from meter to ground side of relay and neg lead on a ground I pull both relays and everything tests right again could i have the wrong asd relay the numbers that napa gave showed 2 diffferent numbers but napa said they were the same? I think its my relay
  • gregjatkinsongregjatkinson Member Posts: 22
    also from what my scematics show is that the fuel relay isnt spose to chatter once power is sent through the fuel and asd relays once running they are a solid circuit when you turn your vehicle on they click on and if you dont start it they click off but that is all the clicking they should do i beleive: my 92 jeep dont click
    So pretty much whatever one is clicking with the other out has a problem somewhere.
    On my 93 once its running with fuel relay out it stops clicking its just a solid circuit.
    So i guess i have 2 look for shorts coming off the fuel relay

    the pcm clicks the injectors and ign coil off and on by controlling thier ground circuit
  • Jaweh999Jaweh999 Member Posts: 9
    Yeah, I had replaced my O2 sensor as well. Another interesting thing is that when I disconnect the MAP sensor everthing seems to work as normal except it will not start when cranking over. The check engine light comes on when key is turned to on position and the fuel pump will run for a second and the pressure will stay up around 40lbs and the relays do not chatter!. So I know my fuel pump is working, something is shutting it off though. I did go ahead and replace the MAP sensor just in case, but that did not change anything. It wil still not start.

    So..I am wondering if the rebuilt PCM is my real problem? Maybe not providing enough current to some of the sensors? Or maybe a broke wire I can't find?

    Wish I knew, I'm already into this beast for a lot.
  • gregjatkinsongregjatkinson Member Posts: 22
    have u traced your map sensor wiring to make sure there is no shorts
    it sounds like we both have a short somewhere in the harness
    I dont beleive it is the pcm even though there is alot that runs through it a short in one little wire will make it look like it could be the pcm

    mine seems like the power feeds are alright but it seems like the pcm is not putting out enough ground to my relays which could very easily be a short in the wiring
  • gregjatkinsongregjatkinson Member Posts: 22
    Also I do beleive if it was the pcm our jeeps would not fire at all
  • gregjatkinsongregjatkinson Member Posts: 22
    right above the pcm there is a connector that has several wires running through it I just happen to see that my fuel pump - oxy sensor wire was melted going into this connector so i started tracing the wires back and its on the fuseblock side of the connector so i disconnected the connector out of the 100 way connection inside the vehicle my ohm meter is reading that the short is towards the fuel pump somewhere (have yet to find) but this explains why my fuel relay would be tripping out
  • Jaweh999Jaweh999 Member Posts: 9
    Yeah, I noticed that wiring block and thought about looking into it. The problem I have is I do not have a schematic to check this out. Is there one on the web that is available? Also, have you tried to pull the connector to your MAP and see if you have the same conditions I have?

    This all started few backs when I had my exhaust manifold changed out. The mechanic did not re-connect my O2 sensor and my check engine light came on after I started driving around the next day. The JCG ran without it connected for awhile and then started giving me issues. I found the problem and reconnected the O2 and it seemed to work ok. THEN, I had my catalytic convertor swappped out because mine had a horrific rattle (been like this for a couple years) and I just got around to having it fixed. It wasn't long after I had the catalytic conver changed out that my JCG died. I wonder if the guys may have shorted out my O2 when they were welding? not sure..I did replace the O2 after my first round of problems but that didnt seem to change anything.

    Just hope the current O2 is good. Is there a way to test these without being powered up?
  • gregjatkinsongregjatkinson Member Posts: 22
    go to scribd.com they have everything you need wire schematics they pretty much have all the paper work the dealer does
  • gregjatkinsongregjatkinson Member Posts: 22
    and yes you test the oxy without being fired up all you do is backprobe the power and ground (not the signal wires) have your meter ready and have someone turn the vehicle on you should get 12 volts for about a second then it goes to 6 volts then none
  • gregjatkinsongregjatkinson Member Posts: 22
    refresh: i started off with my engine fuse blew once - i replaced it ran good for a while then it blew again (knew there had to be something wrong) replaced it a second time and tryed to start the vehicle wouldnt start the only way i could get it to start was by pulling the fuel relay out. so of course its on the fuel relay somewhere. my fuel relay feeds my fuel pump and oxy sensor - fuel pump works fine till you try to start the vehicle. once i tryed starting the vehicle the fuel relay would start chattering (fuel and asd relays should click twice at most) checked voltage at oxy and fuel pump voltage is good. went through testing and replacing alot of sensors didnt help.

    Any how I just happen to see a melted wire going into my inj connector above my pcm started tracing that wire back to the pdc (fuseblock) and found a bare spot on the wire with burn marks right out of the pdc. I disconnected that wire from the pdc left fuel wire in and it works so I guess I have to replace this wire all the way to the oxy sensor.

    It happens to be that the dealership had spliced a wire in right here and from the looks of it they ripped insulation off this wire at the same time creating a month and a half worth of problems. never again will i allow jeep dealerships to touch my jeeps.
  • Jaweh999Jaweh999 Member Posts: 9
    Was the shorted wire obvious or did you have to peel back the protective cover around the bundle?

    "Any how I just happen to see a melted wire going into my inj connector " What is inj connector?
  • gregjatkinsongregjatkinson Member Posts: 22
    first did you go to www.scribd.com/doc/5115283/jeep-1995-yj-fsm-wiring-diagrams and get the info needed for you vehicle they have all the wire diag. plus they have info on how the pcm works inputs & outputs and info on your relay and fuse boxes

    ok above the pcm in my 93 (95 should be the same) there is a wire connector or plug on the firewall my wire going to the oxy sensor was melted i had to pull the harness apart all the way to the fuse block the wire was melted all the way back with other wires

    if yourjeep is doing the same as mine which is not starting till you pull the fuel relay and the fuel relay is causing the chatter and not the asd relay

    then you have the same problem a short on a wire that feeds out of the relay either the ground wire dark blue and yellow stripe wire from pcm slot 51 pcm to ground side of electro magnetic coil in relay or the actual power feed to the fuel pump dark green with black stripe
  • Jaweh999Jaweh999 Member Posts: 9
    Thanks for this great info, my Jeep is a ZJ (Grand Cherokee) so I'll look for that schematic. I have not gone back to the jeep yet, kinda cold in the garage right now so I will be going to get a space heater so I can work out there this evening.

    I have not had any blown fuses and based on what you found I should see something similar (shorted) which I would supsect would cause a blown fuse somewhere. I'll keep looking in and around the harness for a short or broken wire.
  • gregjatkinsongregjatkinson Member Posts: 22
    I just happened to re look over your original messsage.

    yes when you pull the fuel pump relay and it starts fuel pump doesnt prime - you just took the power from your pump pulling the relay.

    look over the schematics on the link i gave you it sounds like you have a short or melted wire too.

    Even though a month ago i found a short on my ign coil trying to fix this problem im on now. the power wire to the coil was bare about 2 inches and bouncing off the frame. Im wondering if this had anything to do with my melted wire. I cant find a real bad short except for the bare spot the dealership obviously made and it only very rarely could actually ground out. so im wondering if a short could backfeed through the relays.

    Any how no matter what you probably have a short going to your fuel pump somewhere. My readings on my meter showed contunity and voltage but there was still a problem there.
  • Jaweh999Jaweh999 Member Posts: 9
    Yeah. I'm fairly certain I have a "short" somewhere and it's most likey under the hood somewhere.

    I'm confident that the short is not in the fuel pump wiring as it will run if I force the fuel realy closed manually. Then I can start the vehicle if I pull the fuel realy..so something is shutting the fuel relay off and I assume that voltage comes from the PCM based on a sensor input. I don't think there is a Inertia / rollover switch on these models so that should be counted out. I'll keep digging...If I find something I will come back and post.

    Thanks
  • Jaweh999Jaweh999 Member Posts: 9
    Found a short in my O2 Sensor harness, close to the connector. The wires were melted together. I couldn't see why it would have happened, the harness didn't look crushed or pinched. Guess the O2 could have shorted out the the wires just got hotter at this particlar place, which caused the meltdown. I'm worried that there could be other shorts in the harness so I'm going to pull the bundles apart and take a look. It's troubling that there are no fuses that could have saved this from happening.
  • gregjatkinsongregjatkinson Member Posts: 22
    ya and I thought I had mine fixed but i didnt

    the short going to my oxy sensor probably the same as yours I couldnt find what could of caused it but I thought i had it running but at the time my fuel pump was not plugged in so when it died it was because i was out of gas

    so when i plugged my fuel pump in by the gas tank my fuel relay started acting up again unplug it and my relay doesnt chatter so i am in the process of pulling my fuel pump out

    i know that my fuel pump works but there is a problem in the fuel pump module you could have the same problem

    it looks like something in my pump went wrong sent a surge back to my fusebox and instead of blowing the engine fuse it melted the wire going to the oxy sensor
  • Jaweh999Jaweh999 Member Posts: 9
    Please let me know if you find an issue with the fuel pump. I did the same thing, unplugged the fuel pump to see if the relay would stopping chattering. I have a replacement PCM coming tomorrow and definitely dont want to plug it in if the fuel pump is bad. I have thought about replacing the fuel pump, before I connect the new PCM, just to be sure my current fuel pump does not short out my new PCM or some other sensor. What stinks is that the tank was recently filled and it's a pain in the rear to drain..I did it 2 years ago. Not looking forward to that but it is probably the best thing to do before I go and plug in my new PCM.
  • Jaweh999Jaweh999 Member Posts: 9
    I finally got my JCG running. I believe the shorted out O2 sensor wires took out my PCM. Once I fixed the shorted wires and got another PCM it started up and is still running fine (knock on wood!). But, the ordigianl problem was hard to put my finger on although I believe it was a problem with the O2 sensor being shorted which most liskey caused the PCM failure?? Im still not 100% sure. I would like to know why there is not a fuse somewhere that could have save the PCM from getting fried.
  • gregjatkinsongregjatkinson Member Posts: 22
    ya on the scensors there is really no fuse for protection i have been thinking about throwing my own inline fuses in so i dont go through this again the only fuse for protection is the engine control fuse but it feeds so much stuff and miles of wiring

    but mine is still not running i pulled my fuel pump and thats it it got cold and started snowing so im trying to get enough room in my garage to keep trying

    but good job im happy to hear its fixed
  • mountanbikermountanbiker Member Posts: 2
    Man it sounds like there is a lot of problems with your jeeps. OK now I have one for you. I own a 2001 Jeep Grand Cherokee Laredo. The battery and alt. or both good. The jeep turns over just fine but wont start all of the time. If I keep playing with the key as in turning it on and off a bunch of times finally i hear the fuel pump kick on and it will start. All of my gauge lights come on but the gauges are dead unless the fuel pump comes on then the gauges read fine and it will start. I also notice that when the fuel pump turns on the light with the key and a line through it goes out but when it don't the light stays on. When i get the jeep to start it runs just fine. I don't think its a pcm problem or it wouldn't run at all would it? If it was the fuel pump then it would shut off while im driving it wouldn't it? Any help would be greatly appreciated. I see that some of you had similar problems but I didnt see what the fix was. Sorry so long but I wanted to let you know all of the info that I have. Thanks.
  • gregjatkinsongregjatkinson Member Posts: 22
    Ya it sounds like you have a short somewhere off your ignition wiring. On my 1992 jeep i had a short in the park/neutral switch wiring and it did exactly what your talking about. my 93 is doing almost the same thing and i am still trying to locate the short
  • dopa911dopa911 Member Posts: 7
    Hey
    I had a 1998 JGC Laredo that I loved vary little problems, sold it and I have a 2001 JGC laredo V8 auto, that I just got,here's the problem, It starts great when cold but when it runs for a while and I shut it off I have to crank it longer then I did when it was cold sometimes longer then others, and it lopes (studders) when I stop at red lights sometimes. I changed the plugs, no distribitor or rotor. I get from reading in the forums it sounds like it might be the Crankshaft Position Sensor? How do I locate it an is a pain to do ? And what about the Oxygen Sensor? Thanks
  • gregjatkinsongregjatkinson Member Posts: 22
    I would test my oxy sensor first then camshaft and crankshaft sensor
  • dopa911dopa911 Member Posts: 7
    Thanks I will. Do you know where the Crankshaft Position Sensor is located? And is a pain to change. Do I have to jack up the front end?
  • gregjatkinsongregjatkinson Member Posts: 22
    on my 93 jeep the crank sensor is right behind the engine on the flywheel and yes it is a pain to get to but you can test it with out pulling it. just need to find the wires that go to it and make sure you are getting proper signal from it
  • dopa911dopa911 Member Posts: 7
    Hey
    I found the crankshaft position sensor location on my 2001 JGCLV8, right behind the starter, had to jack up the front end and pull the starter, bingo, there it was. changed it, seems a little better on the idle side.dosent seem to be as rough, time will tell. Maybe it dosen't seem to crank so much when I go to start it when it's hot !!!!!!! Will post later when and if it is at all better If any other ideas on what I should try per original post please advise.
    Thanks for the replys
  • dopa911dopa911 Member Posts: 7
    I have a 2001 JGC laredo V8 auto, that I just got,here's the problem, It starts great when cold but when it runs for a while and I shut it off and wait about 45min to a hour it starts hard ( Have to crank for around 10 12 seconds is this normal ) have to crank it longer then I did when it was cold sometimes longer then others, I changed the plugs, no distribitor or rotor. I get from reading in the forums it sounds like it might be the Crankshaft Position Sensor? Changed the CPS seems to run smoother but still starts hard when hot What if the battriey is smaller the the orignal? Thanks
  • 03fxdwg03fxdwg Member Posts: 2
    4.0 L with about 150,000 had distributor bushing make screeching nose. Had distributor assembly, wires, cap, rotor and plugs replaced and by independent shop and vehicle began to die while running without any warning. Just seemed as though someone cut off the fuel or there was water in fuel. Live in SC and checked with stations where I fill and used many cans of gas dry without any change. Engine starts back up and runs as though nothing happened for seconds, minutes, hours or days. Had distributor replaced again but problem persisted. Took to Jeep dealer and and had error code for crank position sensor throttle position sensor. Replaced them and then had error for bad PCM. Replaced that with Mopar part and dealer went on to have injectors cleaned, coil replaced after error code showed, Replaced battery and cleaned cable connections. Dealer replaced fuel pump and distributor primary field assembly and problem still persists. Will backfire and miss at speed, stalls at idle or under acceleration or while coasting. Sometimes engine will fire back up and other times I have to coast out of traffic. Sometime when cranking, then engine speed will increase like it wants to run, but isn't getting enough fuel or the spark timing is off. It will usually start right up if you turn off ignition and wait for 15 to 30 seconds, but that is had to do if you are sitting in the middle of an intersection with cars coming at all directions. Dealer is at a loss (no new error codes even though I had a solid check engine light for a day a week ago and then it just went out the next time I started the car. Dealer is replacing PCM under warranty as I have spent over $2500 in the past 9 months.
  • 03fxdwg03fxdwg Member Posts: 2
    New, new MOPAR PCM handled under warranty. Has run without a stall, stutter or back-fire for 9 days. Should have made them try that last August.
  • gregjatkinsongregjatkinson Member Posts: 22
    I have finally got back on to post. the sign in button has not workrd for me for like 3 months. Anyhow i finally found all the issues with my 93 grand cherokee. First i had a short on the power supply to my coil that was touching the frame creating alot of other problems. second i found another short between my tranny and the body coming off the main harness going to my oxy sensor-this one sucked as i had to pull the tranny just to find the short let alone fix it. luckily none of the shorts fried my pcm but every shop in town told me it was my pcm-except for the napa shop they are the ones that told me i had multiple shorts to just replace all the wiring harnesses in the jeep. instead i just rewired it my way the right way. and runs like a charm for having 230,000 miles on the engine
  • jkalvinjkalvin Member Posts: 2
    Can anyone possibly tell me exactly how to find and replace this sensor? I have an intermittent stalling problem. I have checked the fuel pressure and replaced the following:

    Throttle sensor
    Cam Shaft position sensor
    Rotor
    Distributor cap
    All wires
    Coil.

    The dealers have said that I should be able to R&R this sensor without removing any other parts. I can find, what I believe is an oil sensor next to the distributor. Then, behind this, close to the firewall, there is a cable, leading to a connector, which looks like the replacement part I have, but I am not positive it is the correct connector. (The replacement part has some specific markings on the outside, which are not on the part on the car. Is this important?)

    I am not able to see, nor feel the othe end of this wire to confirm that this is the correct sensor. If you have any photos or clear instructions on how to get to this part, I would greatly appreciate your help.
  • rev4revrev4rev Member Posts: 11
    Changed mine on a 94. I believe the dealer fibbed to you. You have to remove the oil sending unit and emission tube just behind and below the oil pressure sending unit. Then plan on some skinned knuckles working back there. That is what the repair manual said anyway and I tried doing it without removing that stuff to no avail. I even thought about boring hole in firewall and coming thru there to get to it but decided on skinned knuckles instead.
  • rev4revrev4rev Member Posts: 11
    Oh also the replacement one i got from the dealer was thinner and they told me to just use shorter bolts. not sure about markings.
  • jkalvinjkalvin Member Posts: 2
    Thank you so very much. I will give that a try. I spent hours yesterday trying it from the side of the valve cover, and earned numerous scratches and scraps and lost a 1/2" socket.
  • toledtoled Member Posts: 1
    The yellow light sign in the control panel stays lightened up with any of both original car keys of my cherokee classic 2001.With this light on car wont start.
    I have a friend who had same problem and in the chrysler service shop told him the PCM had to be replaced.

    Have any of you experienced same problem and solved it without replacing PCM?
    On other hand i've checked pcm sales on line andt they require the VIN number.
    What is the VIN number and where do i find it?
  • axe41axe41 Member Posts: 2
    I have a 1996 Jeep Grand cherokee Larardo 6 yl. It wont start but it turns over. Im getting no spark. Checked the coil and it is not getting power to the coil. Someonoe suggested changing the Power Control Module (PCM). Before I do that is there any other suggestions that my work?
  • gregjatkinsongregjatkinson Member Posts: 22
    i would check your auto shutdown relay your engine fuses and test ohms from the battery to the positive side of the wire going to your coil for shorts first but usually if there are shorts going to your coil they take the pcm out so check for those first before replacing the pcm
  • axe41axe41 Member Posts: 2
    thanks i will try that out and let you know how it works
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