Circuit/System Testing: Notes

Some devices with an internal terminating resistor have a loop in the harness that connects the internal terminating resistor to the serial data circuit. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground or open/high resistance prior to replacing the device for each of the following tests.

Each device may need to be disconnected to isolate a circuit fault. Use the schematics and connector end views to identify the following:

• Powertrain high speed GMLAN devices the vehicle is equipped with
• Powertrain high speed GMLAN serial data circuit terminating resistors
• Device locations on the powertrain high speed GMLAN serial data circuits
• Each device's ground, B+, ignition and powertrain high speed GMLAN serial data circuit terminals