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.
Circuit Description
The GMLAN serial data circuits are high speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. The GMLAN serial data circuits also connect directly to the data link connector (DLC).
Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules.
A CANdi Module is necessary between the scan tool and the ALDL and acts as a transceiver for the scan tool communications with the GMLAN modules. If a CANdi module is not used there may be no communication messages for the specific GMLAN modules.
The scan tool communicates with the following modules on the high speed GMLAN serial data circuits:
- Auxiliary Heater Control Module (FOH) (w/K08, Coolant Heater)
- Engine control module (ECM)
- Glow plug control module (GPCM)
- Transmission control module (TCM)
NO RELATED
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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.