Edmunds Answers



  • MrShift@Edmunds 01/17/09 12:20 pm PST


    1. Disconnect and isolate the battery negative cable. The power seat wire harness connectors for the seat cushion and seat back heating elements are secured to a bracket located under the rear edge of the seat cushion frame. Refer to Wiring for complete circuit schematics and connector locations.
    2. Disconnect the Heated Seat Module (HSM) or Memory Heated Seat Module (MHSM) C2 connector. Check for continuity between the SEAT HEATER B(+) DRIVER circuit cavity of the C2 connector and the seat cushion frame. There should be NO continuity If OK, go to Step 3. If not OK, repair the shorted seat heater B(+) driver circuit as required. NOTE: WHEN CHECKING HEATED SEAT ELEMENTS FOR CONTINUITY, BE CERTAIN TO MOVE THE HEATING ELEMENT BEING CHECKED. MOVING THE ELEMENT, SUCH AS SITTING IN THE SEAT WILL ELIMINATE THE POSSIBILITY OF AN INTERMITTENT OPEN IN THE ELEMENT WHICH WOULD ONLY BE EVIDENT IF THE ELEMENT WAS MOVED IN A CERTAIN DIRECTION. FAILURE TO CHECK THE ELEMENT IN VARIOUS POSITIONS COULD RESULT IN AN INCOMPLETE TEST.
    3. Check for continuity between the SEAT HEATER B(+) DRIVER circuit cavity of the C2 connector and the ground circuit cavity. There should be continuity at all times (even upon moving or sitting in the seat). If OK, proceed with testing the other components in the heated seat system. If not OK, replace the open heating element.

    Following are tests that will help to diagnose the components and circuits that are hard wired inputs or outputs of the heated seat system. However, these tests may not prove conclusive in the diagnosis of this system. In order to obtain conclusive testing of the heated seat system, the Programmable Communications Interface (PCI) data bus network and all of the electronic modules that provide inputs to, or receive outputs from the heated seat system components must be checked.

    The most reliable, efficient, and accurate means to diagnose the heated seat system requires the use of a DRB scan tool and the proper Diagnostic Procedures. The DRB scan tool can provide confirmation that the PCI data bus is functional, that all of the electronic modules are sending and receiving the proper messages on the PCI data bus, and that the Heated Seat Module (HSM) or Memory Heated Seat Module (MHSM) is receiving the proper hard wired inputs and relaying the proper hard wired outputs to perform its heated seat system functions.

    For complete circuit diagrams, refer to Wiring Diagrams.



    Preliminary Test
    Before testing the individual components in the heated seat system, check the following:

    If the heated seat switch LED indicators do not light with the ignition switch in the ON position and the heated seat switch in the Low or High position, check the fused ignition switch output (RUN) fuse in the junction block. If OK, refer to Heated Seat Switch Diagnosis and Testing in this section. If not OK, repair the shorted circuit or component as required and replace the faulty fuse.

    If the heated seat switch LED indicators light, but the heating elements do not heat, check the power seat circuit breaker in the junction block. If OK, refer to Heated Seat Element Diagnosis and Testing in this section. If not OK, replace the faulty power seat circuit breaker.

  • Chechura 02/03/09 10:20 am PST


    Have you solved your problem.
    I have same.
    Inform me please about way for solve.
    Thank you in advance,

  • jimsim 02/08/09 7:55 pm PST

    I too have a 2002 grand cherokee with heated seat problems. I searched for weeks for ways to fix it. I finally read a forum where the guy said that no parts are needed for the fix except soldering gun, wire and some duct tape. My kind of fix. $0. However, there is some sweat to complete this.
    I'll explain in reverse as to keep it all simple. As long as the lights on the heater switches are lighting up you should be in good shape.

    The problem I had was with the way the heater element is installed from the factory. The two wires that separate the rear portion of the element from the frontal portion. That would be the area about 50% between your butt and knees. It's hard to explain but the wires are fed under a horizontal rod that is mounted (left to right) to foam seat and leather seat cover. It helps to hold everything down tight. Problem is that the rod presses on the wires everytime you sit down. The rod eventually wears into the wires and slowly shorts them out and they will eventually break in half as mine did.

    Prepare yourself... If you know nothing about cars. Make sure you employ the help of someone who does before starting. If you want to give it a try anyhow. I will attempt to provide you with a reasonable level of info to get you through it.

    The pros will tell you to test the continuity ohms to see if you have a open condition in the wiring. I chose not to as it was a pain to get the 4 wire connector under the rear of the seat to release.

    I suggest taking the seat out completely as you will have more room to work on it. Only takes a couple minutes to get it out. There is one main connector 6 or 8 pin that goes from carpet up into the seat.

    Lift seat up all the way and put seatback about 50%. Move seat all the way back and take two front seat bolts out. Move seat all the way forward and take two rear seat bolts out. They are located under the plastic covers on the carpet. You need to either pull them straight back or straight up due to the type of clip holding it in. With all bolts out of the seat, tilt it back and lean it against the rear seat. Shine a light from under front of seat. You will see the 6-8 pin connector that needs to be unplugged. There is a red release clip on top the needs to move in the direction toward the door. I am working on drivers seat. Passengers may be a little different. Then squeeze the tang on the connector and it will release pretty easily. Now, if you like your jeep, I would suggest putting a piece of duct tape along the kick panel so you dont scratch it removing the seat. Now that the seat is loose you need to gently lift and spin it 90 degrees so seat bottom is point toward you and headrest is pointed toward the passenger seat. Carefully lift and slide the seat out. Make sure that steering wheel is in the up position. Sit the seat on a card table or equivelent so you have easy access to all sides. This is where it gets interesting. Lean the seat back. You need to take out the hog rings that hold the seat cover on 3 or 4 of them. Two on the console side of the seat and 1 or 2 up front. Needle nose plyers should do it. Push down the seatcover and unclip the seatcover from the rod that secures them. Now the electronics side of the seat. remove the 3 screws holding the cover on. disconnect the two connections. Take out the big bolt that connects to the seat. Just loosen the big bolt on the seat back. Lean the seat up on it's side and unclip the white plastic connector that holds the seat cover down. A screwdriver should pop out the two little clamplocks. The seatcover should be loose on all sides now. You can continue to disconnect the seat motor connections but you may be able to get to the problem now. Turn the seat back on it's back and work the seatcover back. You will be able to get it back about half way before you run into the dreaded cross brace wire that holds the seatcover down. You will need to gently but forcefully slide it out. You should see where the wire burned and toasted the foam by now. if so. strip it back a bit and resolder all tightly back together. Sand wire ends as they have something on them that does not like solder. You can also wire in a bridge with speaker wire if you need some extra. I did. Once soldered up. duct tape everything well and especially the area where the wires are going to come into contact with the wire brace for seatcover. You can slide seat back in car just far enough to reconnect the main connector. Turn key all the way to on but dont start. Check to see if seat warms up. If so, great. Button it all up and enjoy.
    The heat element does not always break at the location I mentioned so you will have to continue on rolling the seat cover back until you find the burned or broken wire. I saw some other pics where the wire broke closer to the rear of the seat.

    See some pics I took that may help and good luck !

    This is the right side wire. The is also another one about an inch or two to the left of this one. You should locate it and fix that one too. I had to take my seat out twice to fix the other side.

    This is the fixed shot. The chunk of duct tape in the middle is wrapped around the wire the holds the seatcover down so it wont come in contact with the wire which I also wrapped in duct tape. Not one of those jobs that you want to do twice... If you dont have to.

    Lastly .... Make sure you close the rear door before trying to put seat back into Jeep. I learned hard way and side swiped my rear door handle with the foot of the seat frame. Very sharp. I have since fixed it.

    There is also a HSM heated seat module that could go bad. Hopefully not. That is expensive. The heated seat element however is normally the culprit from what I have read.

    Good Luck !!!!


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