Hello, Below you will find a description of the heated seats, how they work and some of the components that make up the system. Because the heated seats are a class 2 electronic device and because of the thermistor and all of the modules involved in their operation, there is not much that you can test at home with a test light or a volt meter. The way to test them is with the class 2 scan tool similar to what the dealers use. With the tool each of the components can be function tested to see what ones are with in proper operating perimeters and which ones are not. The tool can be used to command each component to turn on and off as well as running function tests on the whole system to see where the break down is occurring. With the class 2 scan tool, you will be able to pretty much pin point the component or components that have the problem and then you will have a much better idea as to the cost of repairs and then make an informed decision as to what you would like to do. Because of the high cost of some of the parts involved, this is one of those times when is would be far wiser and more cost effective to have the system properly diagnosed, rather than just installing new parts in the hopes of curing the problem. That can get real expensive real fast. If you can find someone who has the correct scanner to run the tests, I would expect the cost to be in the area of an hours labor charge to diagnose. There is also a program change that your truck may need to cure the problem, again requiring the use of the tech 2 scanner, will post it at the bottom.Thanks
Heated Seat Components
The heated seat system consists of the following components:
Heated Seat System Operation
The driver and passenger heated seats have 2 heat zone operating modes with 3 heat level modes and will operate only while the engine is running. The heat zones are determined by which of the 2 heated seat buttons are pressed, while the heat level is determined by the number of times they are pressed. Pressing the seat cushion button 1 time will activate the seat back and cushion heater elements in the high mode. Each time the seat cushion button is pressed the seat back and cushion heat level is reduced from high to medium, low, and off. Pressing the heated seat back button 1 time will activate only the seat back heater element in the high mode. Each time the seat back button is pressed the seat back heat level is reduced from high to medium, low, and off. During heated seat operation the heat zone operating mode may be changed without affecting the current heat level mode.
The heated seat switches are momentary contact switches and are inputs to the driver and passenger door modules. Battery voltage is supplied to the switch assembly from the door module, and when a heated seat switch is pressed and released a brief switch signal voltage is supplied to the door module. Whenever the door module receives an active heated seat switch input, the next heated seat operating mode is determined by whatever the current mode may be. The seat heater elements are controlled by the driver seat module using inputs from the door modules through Class 2 serial data circuit messages. The driver seat module controls the voltage supply and the ground circuits to the seat heater elements. When a heated seat function is commanded active, the seat module will switch battery voltage to the heater element supply circuits, and ground is provided through low side drive control circuits. During heated seat operation both the seat back and cushion heater elements are supplied battery voltage. The seat module grounds the appropriate control circuits for back only or back and cushion heating modes, and opens or closes the active control circuits as necessary in order to maintain the desired seat temperature. The seat module relies on inputs from thermistors located in the driver and passenger seat backs to control heated seat temperatures. The thermistors are 2 wire sensors supplied with a 5-volt referenced signal circuit and a low reference circuit from the seat module. Resistance through the thermistors varies with temperature causing the heated seat sensor signal circuit voltage levels to decrease as the seat back temperatures rise. The seat modules allow heated seat operation only while the engine is running which is determined by a Class 2 serial data circuit message from the powertrain control module.
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.
Driver Seat Module - Reprogram
*This is a unique labor operation number for use only with this bulletin. This number will not be published in the Labor Time Guide.
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