For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit/System Description

The serial data is transmitted over a Local Interconnect Network (LIN) single wire network circuit bus between a primary control module and other control modules within a particular subsystem. If serial data communication is lost between any of the control modules on the LIN bus network, a no communication code against the non-communicating control module will be set. Note: a loss of serial data communications DTC does not represent a failure of the module that set it.

### Diagnostic Aids

• | A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U-code.

• | Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.

• | Communication will be available between the primary control module and the scan tool if there is a loss of communtications with any of the other control modules on the LIN bus network.

• | An open in the LIN bus serial data circuit between the splice pack and a module will only affect that specific module. This type of failure will set a loss of communication DTC for each module effected and the other modules will still communicate.

### Reference Information

#### Schematic Reference

Data Communication Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Data Link Communications Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Testing

Note: Use the schematic to identify the following:

• | Control modules the vehicle is equipped with

• | Control module locations on the LIN bus serial data circuit

• | Each control modules LIN serial data circuit terminals

1. Ignition ON, attempt to communicate with all control modules on the LIN bus serial data circuit. Refer to Data Link References. Communications should not be available with one or more control modules on the LIN bus serial data circuit.

⇒ | If one or more control modules are communicating but not all, refer to Testing the Serial Data Circuit for an Open/High Resistance.

2. Ignition OFF, disconnect the appropriate connector at the primary control module that contains the LIN bus serial data circuit.
3. Ignition ON, test for less than 3 V between the LIN bus serial data circuit connector terminal and ground.

⇒ | If greater than the specified range, test the circuit for a short to voltage. Refer to Testing the Serial Data Circuit for a Short to Voltage.

4. Ignition OFF for 60 seconds, test for greater than 100 Ω between the LIN bus serial data circuit connector terminal and ground.

⇒ | If less than the specified range, test the serial data circuit for a short to ground. Refer to Testing the Serial Data Circuits for a Short to ground.

5. Disconnect the appropriate harness connector that contains the LIN bus serial data circuit at the control module or splice pack, if equipped.
6. Test for less than 2 Ω between the primary control module LIN bus serial data circuit connector terminal and the control module or splice pack, if equipped.

⇒ | If greater than the specified range, test the serial data circuit for an open/high resistance. If the circuits test normal, replace the splice pack, if equipped.

#### Testing the Serial Data Circuits for a Short to Voltage

1. Ignition OFF, disconnect the appropriate harness connector at the control module or splice pack, if equipped.
2. Ignition ON, test for less than 3 V between the LIN bus serial data circuit terminal coming from the primary control module and ground.

⇒ | If greater than the specified range, test the serial data circuit for a short to voltage. If all circuits test normal, replace the primary control module.

3. Test for less than 3 V between each LIN bus serial data circuit at the splice pack connector, if equipped and ground.

⇒ | If greater than the specified range, perform the appropriate test listed below:

• | LIN bus serial data circuits with one control module, test the serial data circuit for a short to voltage. If the circuit tests normal, replace the control module.

• | LIN bus serial data circuits with 2 or more control modules, test each section of the serial data circuit for a short to voltage. If the circuits test normal, replace the control module that causes the short to voltage when connected.

#### Testing the Serial Data Circuits for a Short to Ground

1. Ignition OFF, disconnect the appropriate harness connectors at the control module or splice pack, if equipped.
2. Test for infinite resistance between the LIN bus serial data circuit terminal coming from the primary control module and ground.

⇒ | If not the specified value, test the serial data circuit for a short to ground. If all circuits test normal, replace the primary control module.

3. Ignition OFF for 60 seconds, test for greater than 100 Ω between each LIN bus serial data circuit at the splice pack connector, if equipped and ground.

⇒ | If less than the specified range, perform the appropriate test listed below:

• | LIN bus serial data circuits with one control module, test the serial data circuit for a short to ground. If the circuit tests normal, replace the control module.

• | LIN bus serial data circuits with 2 or more control modules, test each section of the serial data circuit for a short to ground. If the circuits test normal, replace the control module that causes the short to ground when connected.

#### Testing the Serial Data Circuit for an Open/High Resistance

1. Ignition OFF, disconnect the appropriate harness connectors at the control module or splice pack, if equipped.
2. Install a 3 A fused jumper wire between the primary control module LIN bus serial data circuit terminal and the LIN bus serial data circuit terminal at a control module that is not communicating.
3. Ignition ON, verify the scan tool communicates with the control modules connected to the LIN bus serial data circuit.

⇒ | If any control module does not communicate, test each section of the LIN bus serial data circuit for an open/high resistance. If the circuits test normal, replace the control module that does not communicate when connected.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• | GMLAN Wiring Repairs

• | Control Module References for module replacement, setup, and programming