Hello, if the seat light comes on when you turn on the switch, that proves that the fuse and relay are ok in the system. If the seat works part of the time and part of the time it does not, there is a service program change for the control module that will fix it. But if the problem is that it never works, there is a pretty good chance that the heater element has burnt out. This seems to be the most common problem with the seats. You have to physically remove the seat covers to even see the heating element and then if you test it with an ohm meter, you can see if it has any opens spots in it or not. That is where I would begin. To test the test of the system, you will need a class 2 scan tool to run function tests on the control modules and the rest of the system circuits. You would also need a class 2 scan tool to do the reprograming of the module if it is an intermittent problem. Service bulletin from GM below. Thanks
Some customers may comment that occasionally the seat heater will not operate when activated. If the ignition key is cycled OFF and back ON again, the heated seat will operate correctly. Also, on some LB7 diesel engine vehicles, the seat heater may turn itself off during the first 10 minutes of operation. This occurs only with the first activation for the day and works correctly with subsequent activations immediately after the event. These conditions are intermittent and DTC B3941 may be set.
Technicians are to reprogram the driver seat module with an updated software calibration. This new service calibration was released with TIS satellite data update version 6.5 available June 13, 2005. As always, make sure your Tech 2® is updated with the latest software version.