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Circuit/System Testing: Notes

NOTE: 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
  • Mid speed or chassis high speed serial data circuit terminating resistors
  • Control module locations on the serial data circuits
  • Each control modules mid speed or chassis high speed serial data circuit terminals
  1. Attempt to communicate with all control modules on the mid speed or chassis high speed serial data circuit. Refer to Data Link References . Communications should not be available with two or more control modules on the mid speed or chassis high speed serial data circuit.
    • If only one control module is not communicating, diagnose that control module only. Refer to DTC U0100-U02FF .
  2. Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
  3. All access doors closed, ignition OFF for 60 seconds, 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.
  4. Ignition ON, test for less than 3 V between the serial data circuits listed below and ground:
    • Mid speed GMLAN serial data terminal 3
    • Mid speed GMLAN serial data terminal 11
    • Chassis high speed GMLAN serial data terminal 12
    • Chassis high speed GMLAN serial data terminal 13
  5. Ignition OFF for 60 seconds, test for greater than 100 Ω between the serial data circuits listed below and ground:
    • Mid speed GMLAN serial data terminal 3
    • Mid speed GMLAN serial data terminal 11
    • Chassis high speed GMLAN serial data terminal 12
    • Chassis high speed GMLAN serial data terminal 13
  6. Test for 50-70 Ω between the serial data circuits listed below:
    • Mid speed GMLAN serial data circuits terminal 3 and terminal 11
    • Chassis high speed GMLAN serial data circuits terminal 12 and terminal 13
    • If less than 35 Ω, test for a short between the serial data circuits. Refer to Testing the 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 a Open/High Resistance .
    • If infinite, test the serial data circuits between the DLC and the first connection to the serial data circuit for an open/high resistance.
  7. If the circuits test normal, refer to Testing the Ignition Circuit .
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