Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Body Control Modules: Operation
Each class-2 module is programmed with a list of important serial data messages that should be received by other modules. Also contained are default actions taken by the module if one of the important messages is not received in time. One of these messages is the State Of Health (SOH) message. SOH is sent out periodically (if no other message needs to be sent) to let all other modules on serial data link know the sending module is working correctly.
Each module relies on information from another module and incorporates a diagnostic procedure associated with that module. The diagnostic uses the SOH message to perform a diagnostic. Each time ignition is turned on, all modules on class-2 serial data link learn the other modules connected to class-2 serial data link. Modules are able to learn other modules on class-2 serial data link because each important message sent has a source identifier as part of the message.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.