Hi.... I have a 99 300M and the passanger heated seats work only once.... By that I mean everytime you turn on your car, they will work but if you turn them off they won't turn back on..... I was wondering if anyone had any suggestions on what could be the problem....

 

possible memory seat module under the driver side seat.

 

How can I check to see if its the seat module.... and would The drivers side seats work perfectly but the passengers wouldn't

 

there are not really good ways to test a module with out a DRB scanner u wont be able to see the inputs and outputs with out one.
U can smell the module if it smells cooked then that is a good sign of it being bad.
The pass and drive seat is controld by one module.
If u have an ohm meter u can ohm across the seats lower and upper grid to see if u have a broken wire in the seat.

 

I had a similiar problem on my 99 LHS. I've read a lot of stuff saying that most people have replaced the seat or choose not to repair it at all due to $$$. For those willing to put in the time, my seat was easily repaired. I discovered by using a multi-meter and wiring diagrams from Auto zone, I discovered the heating elements in the seat cushion had no resistance there are 2 elements (heating wire) in the seat bottom.
1. Unplug the connectors that come to the floor to the seat.
2. Remove the seat completely from the car.
3. Unbolt the 2 links that recline the seat back.
4. Unbolt the seat back from the seat cushion.
5. Remove screws from the trim that holds the seat controls and pull away from the seat.
6. Disconnect the Green connector with 2 wires under the seat, this is the heating element connection for the back.
7. Lift the back off of the seat.
8. Pull away the seat cover at the base, it comes off easily with your fingers.
9. Carefully lift the seat cover off the foam, only the outer edge of the cover can be pulled back at this time.
10. Using a regular screw driver, place the blade into the "hog rings" and twist. The rings are kind of like a key ring an rotate off easily. There are about 6 and this will allow the remainder of the seat cushion to be pulled back.
11. You will now see about 6 wires soldered to smaller wires glued down to the foam at the rear of the seat. Repair any broken wires and resolder, glue back into place.
12. Follow the other wires going to the front of the seat, this is the element around the back of your knees. Remove the white tape covering the soldered connectors. Using a Multi-Meter, check for any resistance, if none this one is broke also. If the solder connections were o.k., you have a break in the wire somewhere. The heating wire is sandwiched between the foam, you'll will need to pull the foam apart to see the wire. Mine was easily discovered, a small burn mark showed up on the foam where the wire was broke, the insulation was still covering the wire. I Gently pulled the wire and the insulation stretched apart because the wire was broken within. I stripped the wire and resoldered.

This was a repair I thought would be more techincal like the heating module, BCM, or broken ground that I would never find.

This seat is now HOTTTT!

The time spent checking wires using a meter is the way to go. My passanger seat worked fine so by comparing the readings from one seat to the other, It was easy to find the root of the problem.