For 1990-2009 cars

### Diagnostic Instructions

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

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

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

### DTC Descriptors

DTC B1103: SIR Serial Communications Fault

### Circuit/System Description

When the ignition switch is turned to ON, the sensing and diagnostic module (SDM) will perform a turn-on test to diagnose critical malfunctions within the SDM itself.

Upon passing these tests, ignition and deployment loop voltages are measured to ensure that they are within their normal voltage ranges. The SDM monitors the voltages at the driver low and the passenger low to detect shorts to ground or voltage in the deployment loops.

The SDM inspects the wiring connection to each inflator by letting the perpetual current flow through the internal circuit and verify the resistance. If the voltage is out of range, the SDM is unable to inspect the air bag system properly.

### Conditions for Running the DTC

Ignition voltage is between 9-16 volts.

### Conditions for Setting the DTC

The voltage supplied from the battery maintains lower than 10.6 volts for 16 seconds.

### Action Taken When the DTC Sets

The SDM commands the air bag indicator ON.

### Conditions for Clearing the DTC

The condition responsible for setting the DTC no longer exists and the scan tool Clear DTCs function is used.

### Reference Information

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Testing

Important: When removing connectors inspect for damage or corrosion. Damage or corrosion in the following requires repair or replacement of the affected component/connector.

• | The SDM module

• | The SDM wiring harness connector

1. Measure for greater than 10.6 volts at fuse F10.

⇒ | If voltage is less than 10.6V, repair the voltage supply circuit to fuse F10.

2. Disconnect the SDM connector. Refer to SDM replacement in Repair Instructions for connector location.
3. Measure voltage at terminal 26 of SDM connector.

⇒ | If voltage is above 10.6V, replace the SDM.

⇒ | If voltage is less than 10.6V, repair open or high resistance in voltage circuit to SDM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM and SDM replacement, setup, and programming