2008 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.

Seat heater control module failure, like other electronic components, is random, and predictability is guesswork at best. Failure can happen at any rate and any time, however, this is not a common repair. Seat heating systems in most vehicles are seldom used except in cold climates.

When diagnosing the SHCM, the technician will simply compare actual conditions to electronic conditions. In other words, If the technician notes that the seat heating element is actively heating the seat(s), but the control module shows no voltage to the seat heater relay, a discrepancy is noted. Discrepancies like this are commonly used as clues which map to the issue. If the technician finds that the issue originates with the control module, whether by physical or scan testing, the module will be verified defective and replaced.

Like any other control module, the location of the seat heater control module (SHCM) will be identified, and the technician will then begin removing all obstructing components needed to access and remove the control module. Once accessed and removed, the connectors are cleaned and inspected, and the new module will be installed. After all components are reassembled on the vehicle, the technician will program the control module, if needed, and test the operation of the system to ensure the customer complaint has been corrected.

When dealing with electronic systems, especially if the issue pertains to a control module, we recommend thorough diagnostics before replacing parts. In effort to correct an electronic failure, it would be very easy to spend hundreds of dollars replacing components before realizing the issue is more advanced. In the case of electronic failures, diagnostics is a must.

Every possible scenario related to the failure of the seat heater control module can be replicated by one or more failures within the seat heater system. This means that the control module may be blamed for an external issue, or an external component may be blamed for an internal seat heater control module issue. When the issue has been routed to one circuit, the entire circuit should be tested to prove the diagnosis.

Except for the very advanced DIY mechanic with a strong understanding of computerized circuit diagnostics and testing, this repair should be left to a professional. Diagnostics of electronic systems are difficult for the untrained person to perform correctly. Unless safety and diagnostic methods are understood and followed properly, this should be left to a professional.