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.
1. No communication on any high speed GMLAN module
2. 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. The vehicle theft deterrent (VTD) module and ECM exchange information using the
BCM as the gateway module allowing communication between the high and low speed serial data busses. The low speed GMLAN serial data circuit must also be operational for vehicle starting. The high speed GMLAN serial data buss uses two 120 ohm terminating
resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is in the rear fuse block and the other is internal to the ECM.
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 to 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
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information.
Circuit/System Verification
Attempt to communicate with all modules on the high speed GMLAN bus.
| ⇒ | If any high speed module communicates and no DTC beginning with a U exists, refer to
DTC U0100-U0299
. |
Circuit/System Testing
High Speed GMLAN Initial Test
- 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. |
- Ignition OFF, disconnect the harness connector (splice pack comb) at JX 250.
- Install 3A fused jumper wires between the following JX 250 terminals.
| • | Terminal K and terminal A |
| • | Terminal C and terminal M |
- Attempt to communicate with the BCM.
- If communication is established refer to DIAGNOSTIC 1.
- If communication is not established, refer to DIAGNOSTIC 2.
Diagnostic 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. |
- Verify a test lamp does not illuminate between B+ and the following JX 250 terminals.
| ⇒ | If the test lamp illuminates, test the serial data circuit for a short to ground. If the circuits test normal, replace the ECM. |
- Ignition OFF, disconnect following harness connector of the ECM:
- Ignition ON, test for less than 1 volt between ground and JX 250 terminals as follows:
| ⇒ | If greater than the specified range, test the serial data circuit for a short to voltage. |
Diagnostic 2
- Ignition OFF, disconnect the X3 harness connector at the BCM.
- Ignition OFF, test for less than 2 ohms on the serial data circuits between the following harness connector terminals:
| • | DLC terminal 6 and BCM terminal 8 |
| • | DLC terminal 14 and BCM terminal 9 |
| ⇒ | If greater than the specified range, test the serial data circuit for open/high resistance. |
- Ignition OFF, test for infinite resistance between the following serial data circuits of the DLC and ground.
| ⇒ | If less than the specified value, test the serial data circuits for a short to ground. |
- Ignition ON, test for less than 1 volt between the following serial data circuits of the DLC and ground.
| ⇒ | If greater than the specified range, test the serial data circuit for a short to voltage. |
- 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. |
- Ignition OFF, connect the harness connector at the BCM, ECM and JX 250.
- Disconnect the harness connector of the TCM.
- Attempt to communicate with the BCM. Communication should not be available.
| ⇒ | If communication is established, Replace the TCM. |
- Disconnect the harness connector of the fuel system control module (FSCM).
- 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. |
- Disconnect the harness connector of the EBCM.
- 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. |
- 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. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the repair.
