Volvo S40 Seat Heater Control Module Replacement Cost

Modern vehicles with seat warmers depend on seat heater control modules to activate and deactivate the seat heating elements, as well several other functions most will never think about. The control module will monitor passenger inputs for the seat heaters, ensure the temperature is correct for that input, monitor for errors, time the seat heaters for automatic shut off, and relay the seat heater information to other systems on the vehicle.

Control modules tend to work in the same fashion regardless of the system they control and monitor. For the seat heater, the control module is connected to battery power, the seat heating elements, possibly temperature sensors, seat heater relays, seat heater on and off switches, and the common area network (CAN). When input is sent to activate or deactivate the seat heaters, the seat heater control module (SHCM) will signal the relays to send power to the seat heaters until a specific temperature is reached. Once that temperature is reached, a residual amount of power will be sent to the seat heating elements to ensure the seats stay at their set temperature. Simultaneously, the CAN is notified of the SHCM activity, so the information can be displayed where appropriate - possibly the driver information panel or navigation screen.

Erratic operation of the seat heaters sums up most of the symptoms of a failed seat heater control module. The seats may not respond to driver input, may not turn off, may not regulate temperature correctly, or the normal display relating to the seat temperature control settings may become blank due to lack of data.

This is a creature comfort, so there is no urgency in getting the issue repaired. However, if the seats always stay heated, the fuse for the seat heaters should be removed. This will prevent driver fatigue from discomfort, especially on long trips.