Modules communicate along one common Purple wire referred to as class 2 serial data line. Serial data line is used to communicate information between systems. Each system on the serial data line is assigned its own identification number, which is used to identify itself to other modules or systems. Class 2 serial data line also allows communication with scan tool through Data Link Connector (DLC). See Fig 1 . Modules communicating along class 2 serial data line are as follow:

Cellular Telephone Module
Driver Door Module (DDM)
Driver Door Switch Assembly (DDSA)
Electronic Suspension Control Module
Left Middle Door Module (w/V4U)
Left Rear Door Module (LRDM)
Memory Seat Module (MSM)
Navigation Data Processor (w/UY4)
Navigation Radio (w/UY4)
Passenger Front Door Module (PFDM)
Right Front Window Switch (w/B05)
Radio Amplifier
Rear Integration Module (RIM)
Rear A/C-Heater Control
Remote Function Actuator (RFA)
Right Middle Door Module (w/V4U)
Right Rear Door Module (RRDM)
Steering Column Module
Theft Deterrent Module
Vehicle Interface Unit (On-Star(R))

Systems periodically send a State of Health (SOH) message to other systems. If those systems fail to send an SOH message back, a corresponding DTC will be set. Also, any system that cannot communicate properly will set a DTC.

Fig 1: Locating Data Link Connector

Courtesy of GENERAL MOTORS CORP.

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.

Safety Warning

Class 2 Serial Data Line

Use the Manual With the Right Hardware

When to See a Mechanic

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