I will post it in 2 different posts because its too long DB
HEATED SEAT SYSTEM Individually controlled driver and passenger side electrically heated front seats are available factoryinstalled optional equipment on this model, when it is also equipped with the power seat option. The heated seat system allows both the driver and the front seat passenger the option to select one of two seat heating ranges, Low or High, or to turn the individual seat heaters OFF using the heated seat switches located in the center lower bezel near the bottom of the instrument panel center stack. The heated seat switch circuit operates on ignition switched battery current supplied through a fuse in the junction block, only when the ignition switch is in the ON position.
The heated seat system consists of the following components
- Heated seat elements
- Heated seat sensors
- Heated seat module (or memory heated seat module)
- Heated seat switches.
The heated seat system also relies upon resources shared with other electronic modules in the vehicle over the Programmable Communications Interface
(PCI) data bus network. The PCI data bus network allows the sharing of sensor information. This helps to reduce wire harness complexity, internal controller hardware, and component sensor current loads. At the same time, this system provides increased reliability enhanced diagnostics, and allows the addition of many new feature capabilities. For diagnosis of these electronic modules or of the PCI data bus network, the use of a DRB scan tool and the proper Diagnostic Procedures are recommended.
The electronic modules that may affect heated seat system operation are as follows:
- Body Control Module (BCM) - Refer to Body Control Module in Electronic Control Modules for more information.
- Heated Seat Module (HSM) - Refer to Heated Seat Module in Electronic Control Modules for more information.
- Memory Heated Seat Module (MHSM) - If the vehicle is equipped with the Memory System, refer to Memory Seat Module in Electronic Control Modules for more information.
Refer to Power Seats Premium I/III in the Contents of Wiring Diagrams for complete circuit diagrams. Following are general descriptions of the major components in the heated seat system.
The heated seat system will only operate when the ignition switch is in the ON position, and the surface temperature at the front seat heating element sensors is below the designed temperature set points of the system. The heated seat system will not operate in ambient temperatures greater than about
41 °C (105 °F) . The front seat heating elements and sensors are hard wired to the Heated Seat Module (HSM) or the Memory Heated Seat Module (MHSM).
The heated seat switches are hard wired to the
Body Control Module (BCM). The
BCM monitors the heated seat switch inputs, then sends heated seat switch status messages to the HSM or MHSM over the Programmable Communications Interface
(PCI) data bus. The HSM or MHSM contains the control logic for the heated seat system. The HSM or MHSM responds to the heated seat switch status messages, ignition switch status messages, and the front seat heating element sensor inputs by controlling the output to the front seat heating elements through integral solid-state relays.
When a seat heater is turned ON, the sensor located on the
seat cushion electric heater element provides the HSM or MHSM with an input indicating the surface temperature of the seat cushion. If the surface temperature input is below the temperature set point for the selected Low or High heated seat switch position, the HSM or MHSM energizes the integral solid-state relay, which supplies battery current to the heating elements in the seat cushion and back. When the sensor input indicates the correct temperature set point has been achieved, the HSM or MHSM de-energizes the solid-state relay. The HSM or MHSM will continue to cycle the solid-state relay as needed to maintain the temperature set point.
The HSM or MHSM and the seat heater elements operate on non-switched battery current supplied through the power seat circuit breaker in the junction block. However, the HSM or MHSM will automatically turn OFF the heating elements if it detects an open or short in the sensor circuit, a short or open in the heating element circuit causing an excessive current draw, or when the ignition switch is turned to the OFF position.
See the owner's manual in the vehicle glove box for more information on the features, use and operation of the heated seat system.
I WILL POST THE REST
both lights are coming on but not heating up
the front passenger heated leather seat on my 94 volvo 850 turbo is not working. the light on the switch is working but there is no heat being produced. what can i do to correct this problem? i don't want to take it to the dealership beacause i know it can be costly. can you please let me how to fix it, thank you.
LOL - same on my 1994 850. Don't buy the broken wire/seat moving theory as I have not moved the seats, or maybe a couple of times at most.
I am thinking there is a fuse but not found it yet - didn;t see one in the main fuse box so there may be one in the harness to the seats.
Yep the same problem.. The driver seat only not heating.. on my 231,000miles 1996 850gt estate...
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