Circuit/System Testing: Notes

WARNING: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.
The High Voltage Disabling procedure will perform the following tasks:

Identify how to disable high voltage.
Identify how to test for the presence of high voltage.
Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.

Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

Safety glasses with appropriate side shields when within 50 feet of the vehicle, either indoors or outdoors.
Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors.
- Visually and functionally inspect the gloves before use.
- Wear the Insulation gloves at all times when working with the high voltage battery assembly, whether the system is energized or not.

Failure to follow the procedures exactly as written may result in serious injury or death.

NOTE: Some control modules 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 control module for each of the following tests.
Each control module may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following:

Control modules the vehicle is equipped with
High voltage energy management high speed GMLAN serial data circuit terminating resistors
Control module locations on the high voltage energy management high speed GMLAN serial data circuits
Each control module's high voltage energy management high speed GMLAN serial data circuit terminals

Perform the High Voltage Disabling procedure before proceeding with this diagnostic. Refer to High Voltage Disabling .
Reconnect the 12 V battery after performing the high voltage disabling procedure.
Attempt to communicate with all control modules on the high voltage energy management high speed GMLAN serial data circuit. Refer to Data Link References . Communications should not be available with two or more control modules on the high voltage energy management high speed GMLAN serial data circuit.
- If only one control module is not communicating, diagnose that control module only. Refer to DTC U0100-U02FF .
Disconnect the scan tool from the X84 data link connector (DLC). The following tests will be done at the X84B auxiliary data connector.
Ignition OFF and all vehicle systems OFF, key out of the ignition switch, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 Ω between the ground circuit terminal 5 and ground.
- If greater than the specified range, test the ground circuit for an open/high resistance.
Ignition ON, test for less than 4.5 V between the serial data circuits listed below and ground:
- Terminal 3
- Terminal 11
- If greater than the specified range, test the serial data circuit for a short to voltage. Refer to Testing the Serial Data Circuits for a Short to Voltage .
Ignition OFF and all vehicle systems OFF, key out of the ignition switch, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for greater than 100 Ω between the serial data circuits listed below and ground:
- Terminal 3
- Terminal 11
- If not the specified value, test the serial data circuit for a short to ground. Refer to Testing the Serial Data Circuits for a Short to Ground .
Test for 50-70 Ω between the serial data circuits terminal 3 and terminal 11.
- If less than 35 Ω, test for a short between the serial data circuits. Refer to.Testing the Serial Data Circuits for a Short between the Circuits .
- If 35-50 Ω there may be a third terminating resistor between the serial data circuits. This can happen if the incorrect control module is installed. Some control modules are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness.
- If greater than 70 Ω but less than infinite, test the serial data circuit for an open/high resistance. Refer to Testing the Serial Data Circuits for an Open/High Resistance .
- If infinite, test the serial data circuits between the X84B auxiliary data connector and the first connection to the serial data circuit for an open/high resistance.