Circuit/System Testing

High Speed GMLAN Initial Test

1. Test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
   • If greater than the specified range, test the ground circuit for open/high resistance.
2. Ignition OFF, disconnect the harness connector (splice pack comb) at JX 250.
3. Install 3 amp fused jumper wires between the following JX 250 terminals.
   • Terminal K and terminal A
   • Terminal C and terminal M
4. Attempt to communicate with the BCM.
5. If communication is established refer to DIAGNOSTIC 1.
6. If communication is not established, refer to DIAGNOSTIC 2.

Diagnostic 1

1. Ignition OFF, test for 108-132 ohms between terminals B and L of JX 250.
   • If greater than the specified range, test the serial data circuits between the ECM and JX 250 for an open/high resistance. If the circuits test normal, replace the ECM.
   • If less than the specified range, test the serial data circuits between the ECM and JX 250 for a short together. If the circuits test normal, replace the ECM.
2. Verify a test lamp does not illuminate between B+ and the following JX 250 terminals.
   • A
   • M
   • If the test lamp illuminates, test the serial data circuit for a short to ground. If the circuits test normal, replace the ECM.
3. Ignition OFF, disconnect following harness connector of the ECM:
   • RPO LU3 - X1
   • RPO LMF/L42/L46U3 - X1
   • RPO LMM - X1
4. Ignition ON, test for less than 1 volt between ground and JX 250 terminals as follows:
   • A
   • M
   • If greater than the specified range, test the serial data circuit for a short to voltage.

Diagnostic 2

1. Ignition OFF, disconnect the X3 harness connector at the BCM.
2. Ignition OFF, test for less than 2 ohms between the DLC serial data circuit terminal 6 and BCM serial data circuit terminal 8.
   • If greater than the specified range, test the serial data circuit for open/high resistance.
3. Ignition OFF, test for infinite resistance between the following serial data circuits of the DLC and ground.
   • Terminal 6
   • Terminal 14
   • If less than the specified value, test the serial data circuits for a short to ground.
4. Ignition ON, test for less than 1 volt between the following serial data circuits of the DLC and ground.
   • Terminal 6
   • Terminal 14
   • If greater than the specified range, test the serial data circuit for a short to voltage.
5. Ignition OFF, test for infinite resistance between the DLC serial data circuit terminal 6 and terminal 14.
   • If less than the specified value, test for a short between the serial data circuits.
6. Ignition OFF, connect the harness connector at the BCM, ECM and JX 250.
7. Disconnect the harness connector of the TCM.
8. Attempt to communicate with the BCM. Communication should not be available.
   • If communication is established, Replace the TCM.
9. Disconnect the harness connector of the fuel system control module (FSCM).
10. Attempt to communicate with the BCM. Communication should not be available.
    • If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the FSCM and the TCM including the jumper in the TCM harness to the data link resistor. If the circuits test normal, replace the FSCM.
11. Disconnect the harness connector of the EBCM.
12. Attempt to communicate with the BCM. Communication should not be available.
    • If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the EBCM and the last module disconnected (including the jumper in the TCM harness to the data link resistor if the TCM was the last module). If the circuits test normal, replace the EBCM.
13. Disconnect the X3 harness connector of the BCM. Test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the BCM and the EBCM.
    • If the circuits test normal, replace the BCM.