Heated Seat repair

[msu-dawg]

I recently bought a 2001 Cherokee Limited and found the seat heaters not working. I searched for info all over the net and found very little. I finally dove into the project today and figured I'd post the info I have for others who may be interested. Yes, I know what some of you think of heated seats, but my wife would disagree and the Jeep is hers..

Symptoms: When I pressed either High or Low on both driver and passenger seat, the high LED would blink on and off for a minute or so and them go out. And no heat from seat.

Preliminary Diagnosis: The info on the net led me to believe that I likely had an open circuit on my heating element.

What I found: I removed the passenger seat first and brought into house to work on. I found that there are three connectors on the backside of the seat that have wire bundles running under the seat cover. Two of them are 2-wire connectors and one is 4-wire. Checking continuity on the seat side of the 2-wire circuits, I found one read about 1.3 Ohms and the outher was open.

I lifted the seat cover off the lower portion of the seat, exposing the foam to find the connection on the underneath side of the seat cover where the power wires (coming from above described connector) were soldered to the heating element wire. This heating element wire is made into the seat cover underside as I had read on some posts/sites. I would definitely believe that the dealership repair would involve replacment of seat covers because of this design.

The Problem: The point where I could see the wires showed a burn spot and the wire was broken. On this seat, I used a short piece of relatively small gauge wire and soldered the transmission wire back to the heater element wire. This gave me a resistance reading of about 1.1 Ohms (which could be a problem- may cause too high a current flow and further overheating).

The Results: When I put the seat back together and installed in Jeep, the heated seat button now indicates seat is working properly. I didn't give it time to heat up as it was 90 degrees outside and I didn't want any more heat right now! I found nearly identical problem on driver side seat and repaired in similar fashion (no spliced in wire- I had enough length on original heater element that I simply soldered it back together).

Potential Problems: The driver and passenger side heater elements ended up at 1.0 and 1.1 Ohms respectively after repair. This compares with 1.3 Ohms on the undamaged element (each seat appears to have 2) on each seat. Assuming the original resistence of the repaired elements was 1.3, the lower resistence will cause higher current and thus may cause the element to burn out quickly. Also, I'm assuming the 4-wire connector may be some sort of thermostat or temperature sense device to allow the system to modulate the heaters as required to maintain temp. If this is not working properly then the heater may stay on constantly and get too hot (and burn itself out, along with my wifes rear!!). It will be a few more months before I will be able to say if my repair is truly successful (come on winter!!!).

Pictures: See pictures at
http://personal.lig.bellsouth.net/m/k/mkcraft/seat1-1.jpg
http://personal.lig.bellsouth.net/m/k/mkcraft/seat1-2.jpg
http://personal.lig.bellsouth.net/m/k/mkcraft/seat2-1.jpg
http://personal.lig.bellsouth.net/m/k/mkcraft/seat2-2.jpg

[JEEPZZ]

Here's some info I found a while back:


DIAGNOSIS AND TESTING - HEATED SEAT SYSTEM
Refer toWiring Diagrams for the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, further details on wire harness routing and retention, as well as pin-out and location views for the various wire harness connectors, splices and grounds.

NOTE: DO NOT ATTEMPT TO SWAP HEATED SEAT MODULES FROM ONE VEHICLE TO ANOTHER. MOST OF THESE MODULES ARE VEHICLE FEATURE SPECIFIC AND THEREFORE NOT INTERCHANGEABLE. ALWAYS USE THE CORRECT PART NUMBERED MODULE WHEN DIAGNOSING OR REPLACING A MODULE.

HEATED SEAT SYSTEM DIAGNOSIS
CONDITION POSSIBLE CAUSES CORRECTION
NO HEATED SEAT SWITCH ILLUMINATION WITH IGNITION ON 1. Faulty fuse. 1. Check heated seat fuse in Junction Block (JB). Replace fuse, if required.
2. Wiring faulty. 2. Check fused ignition switch output (run-acc) circuit from heated seat switch connector to ignition switch. Repair, if required.
3. Ground faulty. 3. Check for ground at heated seat switch connector. Repair, if required.
4. Faulty switch. 4. Refer to Heated Seat Switch for the proper switch diagnosis and testing procedures.
SEATS HEAT, BUT NO HEATED SEAT SWITCH INDICATORS 1. Wiring faulty. 1. Check LED driver circuit(s) from heated seat switch connecvtor to heated seat module connector. Repair, if required.
2. Faulty switch LED. 2. Replace switch with known good unit. If OK, discard faulty switch.
3. Faulty module. 3. Refer to Heated Seat Module for the proper module diagnosis and testing procedures. Replace, if required.
SEATS DO NOT HEAT AND NO HEATED SEAT SWITCH INDICATORS 1. Faulty circuit breaker. 1. Check power seat circuit breaker in Junction Block (JB). Replace, if required.
2. Faulty relay. 2. Refer to Heated Seat Relay for the proper relay diagnosis and testing procedures. Replace, if required.
3. Faulty module. 3. Refer to Heated Seat Module for the proper module diagnosis and testing procedures. Replace, if required.
HEATED SEAT SWITCH INDICATORS FLASHING 1. Faulty sensor. 1. Refer to Heated Seat Sensor for the proper heated seat system self-diagnostic routine. Repair, as required.
2. Faulty element. 2. Refer to Heated Seat Element for the proper heated seat system self-diagnostic routine. Repair, as required.


SELF-DIAGNOSTICS - HEATED SEAT SYSTEM
The heated seat system is capable of performing some self-diagnostics. The following table depicts the various failure modes which will be reported to the occupant via flashing of the heated seat switch Light-Emitting Diode (LED) indicators. Flashing LED indicators on the driver side switch indicate that a fault exists in the driver side portion of the system and, likewise, flashing LED indicators on the passenger side switch indicate a fault exists in the passenger side portion of the system. The LED indicators will flash at a rate of approximately one-half second on, and one-half second off for a duration of one minute. This process will repeat each time an attempt is made to turn the system on with the heated seat switches until the problem has been corrected.

HEATED SEAT SYSTEM SELF-DIAGNOSTIC TABLE
FAILURE MODE SWITCH "HI" LED INDICATOR SWITCH "LO" LED INDICATOR
Shorted Heating Element Flashing Flashing
Open Heating Element Flashing Off
NTC Sensor Value Out of Range Off Flashing

[JEEPZZ]

So what's the update now that cold weather is setting in?

[msu-dawg]

Originally Posted by JEEPZZ

So what's the update now that cold weather is setting in?

Well, today has really been the first day that might have been cold enough to think about using the heaters. Wife is driving the jeep, as usual and hasn't gotten in from work so I don't know if she turned it on or not.

I have played with them a couple of times since the repair, both driver and passenger, and they're still working. In HI they get very warm, very quickly. In LOW, I have trouble telling they're on, but I have not left them on in LOW for any length of time either.

The weather gurus say it's supposed to get down to 44 tomorrow night so maybe I'll go driving and try the heater out.

[JEEPZZ]

I'm in the process of installing a complete leather interior from a 99 Limited. I tested out the seat motors and heaters. The only problem I had was the drivers seat wouldn't heat up. I ran down the diagnostics list in the FSM and found that I had no continuity in the drivers seat cushion. (the seat heaters are wired in series) The FSM says that the cushion must be replaced as it is not a repairable item. I dug up this thread from way back and decided to give it a try. My heater wire was broken in the exact same place as yours so I soldered it back together and gave it a try. With a 45* ambient temperature, both seats turned on high measured up to 95* on a pyrometer within 30 seconds.
Thanks for the tip and I hope yours work out as good mine.

[msu-dawg]

JEEPZZ- glad to hear that it has worked out well for you. The day I wrote the previous reply wife called and wanted to go out for dinner so she picked me up here at the house in the Jeep. It was fairly cool out so I turned the heaters on high for the trip to the restaurant... VERY NICE! I may have to install some of those in my F150! Now I just hope my repair job holds up for a while!

[magicman]

hello, read your posts about heated seat problems! I have an 01 limited, my seats worked great last winter but now when I turn them on the light on the switch comes on but the seats dont heat up? all the post I have read said that there led flashes indicating a problem?
is there any way to check this without having to take the seats out? I would rather not take it to the shop so they can rip me off? is there a fuse maybe for this?
thanks for any help
Greg

[JEEPZZ]

Originally Posted by magicman

all the post I have read said that there led flashes indicating a problem?

Do your switches flash or even light up indicating power?

[msu-dawg]

Originally Posted by magicman

hello, read your posts about heated seat problems! I have an 01 limited, my seats worked great last winter but now when I turn them on the light on the switch comes on but the seats dont heat up? all the post I have read said that there led flashes indicating a problem?
is there any way to check this without having to take the seats out? I would rather not take it to the shop so they can rip me off? is there a fuse maybe for this?
thanks for any help
Greg

Light(s) flashing seems to be the typical indicator of a problem with which lights that are flashing giving info on the nature of the problem. If I understand correctly, your light is not flashing but seats do not heat up. Do the lights work properly- i.e. when you select high the high led lights steady up and same for low? I'll take a look at schematics tomorrow and see if I can figure anything else like a main power fuse.

Mike

[msu-dawg]

magicman, are you still out there? Still having a problem?

the service manual doesn't describe a condition that would have the heater HI or LOW led on steady with the heaters not working. It describes conditions of the HI light flashing (heater element problem) or the LOW light flashing (temp sense circuit problem) or no led light at all (but with heaters working).

Looking at the wiring diagram-

Fuse 18 (10A) gives power to the heater switches (by way of the ignition switch). The switch selection LEDs and the switch illumination LEDs (the green ones) both get their power from this source. Switch then sends signal to the SHIM (Seat Heater Interface Module). This is a plastic box (mine is white in color) that is mounted underneath the passenger seat.

Fuse 29 (25A) supplies the power that eventually energizes the heater elements. It first goes to the Heated Seat Relay (also mounted under the passenger seat). The relay contacts are closed when the ign switch is in run or acc (coil power comes from fuse 18 described above). Power then goes to the SHIM where the SHIM determines when to put voltage to the heating coils, based on the input from the seat switches and the input from the seat temp element. Fuse 29 also supplies power to electric seats so if they don't work then I'd check that.

Book doesn't say whether or not the SHIM will make the lights indicate normally if it is not receiving power but my guess is that it wouldn't. If I get time tomorrow I may check that by pulling my fuse and trying it.

So, my suggestions would be to check fuse 29 and check the relay to see if it is working- this would be easy enough with a multi-meter, a couple of wires and your battery.

If you're still reading this post, let me know if you need more info.


Mike

[JEEPZZ]

Mike, one last question for you. Do you seat heater switches always stay illuminated with the key on? (not the high or low LED's but the backlighting) I'm just curious because mine do. They don't shut off when the headlights are off like all the other interior lights but they do once the key is in the off position. I'm also not able to dim them with the interior and dash lights rheostat.
I just want to make sure I have it wired up correctly since I had to make my own wiring for it. 97's didn't have both front power seats as an option yet alone heated ones.

[magicman]

hello all, sorry it took so long I run my own business and it was a hectic weekend! the lights on my switch(hi or low heat for the seats) when I turn them on they stay on steady(they are orange not green as someone else said) both positions for both seats stay on steady, and they turn off when I turn the switch to off but the seats are just not heating up, I will try a few of the suggestions and see how it goes............I would really like to get it fixed , we just got our first snow storm here in Massachussetts and I missed them!

[msu-dawg]

Originally Posted by magicman

(they are orange not green as someone else said)

The green lights I refered to are the LEDs that illuminate the switch (so you can see it in the dark). Yes, the switch position LEDs (HI, LO) are orange.

JEEPZZ, yes the green LEDs are illuminated anytime the key is in run or acc. and they are not affected by the dimmer rheostat. And this mode of operation agrees with the wiring diagram in the FSM.

I pulled the power seat circuit breaker (listed as a CB rather than a fuse) to see if this would produce the problem that you are having since it is the power source for the current that actually heats the elements. No such luck- with the PS CB removed (it's difficult to get to BTW due to the small opening they give you for the fuse cover) the heated seat indicators just didn't do anything- no light from either one. This make sense as the SHIM is not receiving power. Of course, the green illumination still worked!!!

Here's my best thought- since last you knew both seats were working (this is true, right?) and now all of a sudden they are not, it would seem to be something common to both. This rules out the heater elements and the temp sense thermistors, since these are independent to each seat. That pretty well leaves the SHIM as being the faulty item. I'm sure someone with an electronics background may be able to fix this type of thing, but it would be way over my head. And I would doubt the Chrysler stealership is just giving them away.

Sorry I couldn't be more help on your problem. If I'm hit with a heated seat epiphany in my sleep I'll get back with you!

[msu-dawg]

Originally Posted by magicman

we just got our first snow storm here in Massachussetts and I missed them!

P.S. Oh how I wish I could get snow!!

[magicman]

well thanks for the response........next time maybe you try it in english LOL guess I'll be bringing to the shop!