Circuit Description
The inflatable restraint sensing and diagnostic module (SDM) monitors the front end discriminating sensor circuit for front impact detection. The SDM processes the signal provided by the front end discriminating sensor to further support deployment of the air bags. The front end discriminating sensor is an input only to the SDM and does not directly cause air bag deployment. When you first turn the ignition switch to the RUN position, the inflatable restraint sensing and diagnostic module (SDM) performs tests to diagnose critical malfunctions within itself. The SDM then performs the following continuous diagnostic tests on the deployment loops:
| • | Deployment loop voltage out of range test |
| • | Deployment loop resistance measurement test |
If the voltage out of range test detects a short to voltage condition, the resistance measurement test for that deployment loop will not be performed.
Conditions for Setting the DTC
The SDM detects the voltage at the discriminating sensor signal input is 0.5 volts or less for 500 milliseconds.
Action Taken When the DTC Sets
| • | The SDM disables the discriminating sensor input. |
| • | The SDM commands ON the AIR BAG warning lamp via Class 2 serial data. |
Conditions for Clearing the DTC
| • | The voltage at the discriminating sensor signal input is greater than 0.5 volts for 500 milliseconds. |
| • | You issue a scan tool CLEAR CODES command. |
| • | A history DTC will clear once 255 malfunction free ignition cycles have occurred. |
When the SDM detects that no DTCs are present, the SDM commands the AIR BAG warning lamp OFF.
Diagnostic Aids
A broken or chafed wire in the inflatable restraint front end discriminating sensor circuit may cause an intermittent condition to occur. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
Tests for a malfunctioning discriminating sensor.
-
Tests for a short to ground in the discriminating sensor input circuit.
-
Tests isolates a short to ground in the discriminating sensor input circuit to one side of the in-line connector.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: SIR Schematics Connector End View Reference: SIR Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - SIR? | -- | Go to Step 2 | |
Does the resistance measure more than the specified value? | 950 ohms | Go to Step 3 | Go to Step 7 | |
Does the resistance measure less than the specified value? | OL | Go to Step 4 | ||
Does the resistance measure less than the specified value? | OL | Go to Step 5 | Go to Step 6 | |
5 | Locate and repair a short to ground in the discriminating sensor input circuit between the discriminating sensor in-line harness connector and the discriminating sensor harness connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 8 | -- |
6 | Locate and repair a short to ground in the discriminating sensor input circuit between the discriminating sensor in-line harness connector and the inflatable restraint sensing and diagnostic module (SDM) harness connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 8 | -- |
7 | Replace the inflatable restraint front end discriminating sensor. Refer to Inflatable Restraint Front End Discriminating Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- |
8 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
