Circuit/System Verification

Perform Circuit/System Verification using one of the following two methods:

Verifying the Serial Data Circuits using Data Bus Diagnostic Tool

1. Using schematics and vehicle build information, identify all high speed GMLAN devices the tested vehicle is equipped with, terminating resistors, and each device location on the high speed GMLAN bus.
2. Ignition ON/Vehicle In Service Mode.
3. From Data Circuit input selection, select Terminal 6, 14 to test the high speed GMLAN serial data bus.
4. Start the test and verify the Detected State parameter is displayed as OK.
   • If the Detected State parameter is displayed as Control Module Not Awake 

     Refer to Circuit/System Testing - Testing the Device Circuits.

   • If the Detected State parameter is displayed as Control Module Ground Connection Malfunction 

     Refer to Circuit/System Testing - Testing the Device Circuits.

   • If the Detected State parameter is displayed as CAN Bus [+] (pin 6) Circuit Shorted to High Voltage or CAN Bus [-] (pin 14) Circuit Shorted to High Voltage 

     Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage.

   • If the Detected State parameter is displayed as CAN Bus [+] (pin 6) Circuit Shorted to Low Voltage or CAN Bus [-] (pin 14) Circuit Shorted to Low Voltage 

     Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground.

   • If the Detected State parameter is displayed as CAN Bus [-] Shorted to Bus [+] 

     Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits.

   • If the Detected State parameter is displayed as CAN Bus Open with one or more non responding high speed GMLAN devices 

     Refer to Circuit/System Testing - Testing the Serial Data Circuits for an Open/High Resistance (Data Bus Diagnostic Tool).

   • If the Detected State parameter is displayed as CAN Bus Open and all high speed GMLAN devices are responding 

     Repair the open/high resistance in the circuit between the external terminating resistor and the closet responding device.

   • If the Detected State parameter is displayed as OK and none of the high speed GMLAN devices are responding 

     Repair the open/high resistance in the circuit between the X84 Data Link Connector and the first splice/device in the serial data circuit. If the circuit tests normal, check the MDI cable and the connection at X84 Data Link Connector prior to replacing the first device or splice pack.

   • If the Detected State parameter is displayed as OK and one or more high speed GMLAN devices are not responding 

     Refer to Circuit/System Testing - Testing the Device Circuits to test the non responding device closest to a responding device.

   • Go to next step: If the Detected State parameter is displayed as OK and all high speed GMLAN devices are responding 
5. All OK.

Verifying the Serial Data Circuits using Digital Multimeter

1. Ignition ON/Vehicle In Service Mode.
2. Verify two or more devices are not communicating on the high speed GMLAN serial data circuit. Refer to Data Link References  to determine how many devices should be communicating on the high speed GMLAN bus.
   • If only one device is not communicating 

     Refer to Circuit/System Testing - Testing the Device Circuits.

   • Go to next step: If two or more devices are not communicating 
3. Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down. Disconnect the scan tool from the X84 Data Link Connector. The following tests will be done at the X84 Data Link Connector.
4. Test for less than 10 Ω between the ground circuit terminal 5 and ground.
   • If 10 Ω or greater 
   1. Ignition/Vehicle OFF.
   2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
   • Go to next step: If less than 10 Ω 
5. Ignition ON/Vehicle In Service Mode.
6. Test for less than 4.5 V between the serial data circuits listed below and ground.
   • Terminal 6
   • Terminal 14
   • If 4.5 V or greater 

     Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage.

   • Go to next step: If less than 4.5 V 
7. Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down.
8. Test for greater than 100 Ω between the serial data circuits listed below and ground.
   • Terminal 6
   • Terminal 14
   • If 100 Ω or less 

     Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground.

   • Go to next step: If greater than 100 Ω 
9. Test for 50 - 70 Ω between the serial data circuit terminals 6 and 14.
   • If less than 35 Ω 

     Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits.

   • If between 35 - 50 Ω 

     There may be a third terminating resistor between the serial data circuits. This can happen if the incorrect device is installed. Some devices are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness. Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits.

   • If greater than 70 Ω but less than infinite 

     Refer to Circuit/System Testing - Testing the Serial Data Circuits for an Open/High Resistance (Digital Multimeter).

   • If infinite resistance 

     Repair the open/high resistance in the circuit between the X84 Data Link Connector and the first splice/device in the serial data circuit.

   • Go to next step: If between 50 - 70 Ω 
10. Refer to Circuit/System Testing - Testing the Device Circuits.