Diagnostic Instructions
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
High Speed GMLAN Serial Data (+)
| 1
| 2*
| 1
| --
|
High Speed GMLAN Serial Data (-)
| 1
| 2*
| 1
| --
|
Ground (DLC, terminal 5)
| --
| 1
| --
| --
|
Battery Positive Voltage (B+)
| 1
| 1
| --
| --
|
* An open between the data link connector (DLC) and the first splice will only effect the communication with the scan tool. The vehicle modules will still communicate.
- No communication on any high speed GMLAN module
- An open in only one high speed GMLAN serial data circuit may allow degraded communication between the modules
|
Circuit/System Description
Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other
than OFF. The high speed GMLAN serial data circuits must be operational for the vehicle to start due to body control module (BCM) and engine control module (ECM) communications.
Diagnostic Aids
| • | Communication may be available between the BCM and the scan tool with the high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the high and low speed GMLAN systems. |
| • | This test is used for a total high speed GMLAN communication failure. If only one module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics. |
| • | An open in the DLC ground circuit terminal 5 will allow the scan tool to operate and set up the vehicle on the tool and then not communicate with the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the
scan tool will indicate "no CANdi module detected" and will not communicate. |
| • | The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus. |
| | The following conditions may cause a total loss of high speed GMLAN data communication: |
| - | A short between high speed GMLAN (+) and high speed GMLAN (-) circuits |
| - | Any of the high speed GMLAN serial data circuits shorted to ground or voltage |
| - | A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits |
Reference Information
Schematic Reference
Connector End View Reference
Component Connector End Views
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
Circuit/System Testing
- Test for less than 1.0 ohm between the ground circuit terminal 5 of the DLC and ground.
| ⇒ | If greater than the specified range, test the ground circuit for open/high resistance. |
- Remove the terminator resistor.
- Test for 110-130 ohms between the terminals of the resistor.
| ⇒ | If not within the specified range, replace the resistor. |
- Connect the terminator resistor.
- Ignition OFF, disconnect the harness connector X3 at the BCM.
- Test for less than 2 ohms on the serial data circuit between terminal 6 of the DLC and terminal 8 of the BCM.
| ⇒ | If greater than the specified range, test the serial data circuit for open/high resistance. |
- Verify a test lamp illuminates between each ground circuit terminal of the BCM listed below and B+.
| ⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance. |
- Ignition OFF, disconnect the harness connector X4 of the BCM.
- Ignition ON, verify a test lamp illuminates between each B+ circuit terminal of the BCM listed below and ground.
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or short to ground. |
- Ignition OFF, disconnect the harness connector of the EBCM.
- Ignition ON, test for less than 1 volt between the serial data circuit terminal 6 of the DLC and ground, and terminal 14 of the DLC and ground.
| ⇒ | If greater than the specified range, test the serial data circuit for a short to voltage. |
- Test for infinite resistance between the serial data circuit terminal 6 of the DLC and ground, and terminal 14 of the DLC and ground.
| ⇒ | If less than the specified value, test the serial data circuit for a short to ground. |
- Test for infinite resistance between the serial data circuits terminal 6 and terminal 14 of the DLC.
| ⇒ | If less than the specified value, test the serial data circuits for a short between them. |
- Connect the harness connectors of the BCM and the EBCM.
- Disconnect the harness connector X3 of the ECM.
- Attempt to communicate with the vehhicle communication interface module (VCIM). Communication should not be available.
| ⇒ | If communication is available, replace the ECM. |
- Ignition OFF, disconnect the harness connector X1 of the right headlamp module, if equipped with RPO TSH.
- Attempt to communicate with the VCIM. Communication should not be available.
| ⇒ | If communication is available, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the ECM and the right headlamp module. If the circuits test normal, replace the right headlamp module. |
- Ignition OFF, disconnect the harness connector X1 of the TCM.
- Attempt to communicate with the VCIM. Communication should not be available.
| ⇒ | If communication is available, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the TCM and the module listed. If the circuits test normal, replace the TCM. |
| • | Right headlamp module - with TSH |
- Ignition OFF, disconnect the harness connector of the EBCM.
- Attempt to communicate with the VCIM. Communication should not be available.
| ⇒ | If communication is available, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the EBCM and the TCM. If the circuits test normal, replace the EBCM. |
- Ignition OFF, connect the harness connectors of the EBCM, TCM, ECM, and the right headlamp module.
- Ignition OFF, disconnect the harness connector X2 of the rear differential clutch control module, if equiped with RPO MH6.
- Attempt to communicate with the EBCM. Communication should not be available.
| ⇒ | If communication is available, replace the rear differential clutch control module. |
- Ignition OFF, disconnect the harness connectors X1 and, X2 of the VCIM. Attempt to communicate with the EBCM. Communication should not be available.
| ⇒ | If equipped with RPO MH6, and communication is available, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the VCIM and the rear differential clutch control module. If the circuits test
normal, replace the VCIM. |
| ⇒ | If not equipped with RPO MH6, and communication is available, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the VCIM and the data link resistor. If the circuits test normal, replace
the VCIM. |
- Ignition OFF, disconnect the harness connector X3 of the BCM.
- Ignition ON, test for less than 1 volt between the serial data circuits of BCM terminal 8 and ground, and between BCM terminal 9 and ground.
| ⇒ | If greater than the specified range, test the circuit for a short to voltage. |
- Test for infinite resistance between the serial data circuits of BCM terminal 8 and ground, and between BCM terminal 9 and ground.
| ⇒ | If less than the specified value, test the circuit for a short to ground. |
- Test for infinite resistance between the serial data circuits terminal 8 terminal 9 of the BCM.
| ⇒ | If less than the specified value, test the serial data circuits for a short between them. |
- If the circuits test normal, replace the BCM.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the repair.
