GM Service Manual Online
For 1990-2009 cars only

Circuit 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, the ignition and deployment loop voltages are measured to ensure that these voltages are within the normal 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 tests the wiring connection to extra devices, such as the side impact sensor, by letting an infinitesimal current flow through the internal circuit to verify the resistance. If the voltage is out of range, the SDM is unable to test the airbag system properly.

In the case of DTC B1103, test the battery and if necessary replace the battery with a new one. Erase the DTC using the scan tool.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1326 Front End Sensor 1 Short to Ground

Conditions for Running the DTC

Ignition voltage is within the normal operating voltage range.

Conditions for Setting the DTC

The left early crash sensor wiring is shorted to ground.

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.

Caution: The sensing and the diagnosis module (SDM) can maintain sufficient voltage to deploy the airbags and pretensioners for up to 1 minute after the ignition has been turned OFF and the fuse has been removed. If the airbags and pretensioners are not disconnected, do not begin service until one minute has been passed after disconnecting power to the SDM. Failure to do so may cause personal injury.

Caution: Do not strike or jolt the inflatable restraint sensing and diagnostic module (SDM). Before applying power to the SDM, make sure that it is securely fastened with the arrow facing toward the front of the vehicle. Failure to observe the correct installation procedure could cause SIR deployment, personal injury, or unnecessary SIR system repairs.

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 - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn the ignition switch to OFF.
  2. Wait 60 seconds for the sensing and diagnostic module (SDM) charger to discharge.

Is the SDM charger discharged?

--

Go to Step 3

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3

Visually inspect for damage to the left early crash sensor wiring.

Is the early crash sensor wiring damaged?

--

Go to Step 4

Go to Step 5

4

Replace the airbag wiring.

Did you complete the replacement?

--

Go to Step 8

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5

  1. Turn the ignition switch to OFF.
  2. Disconnect the left early crash sensor connector.
  3. Disconnect the SDM connector.
  4. Test the resistance between the terminal 74, 75 of the SDM and ground.
  5. Test the resistance between the terminal 74 and 75 of the SDM connector.

Are the resistances approximately equal to the indicated value?

Go to Step 6

Go to Step 4

6

  1. Replace the left early crash sensor.
  2. Verify that all components, connectors, and connector position assurances (CPAs) are properly mounted.
  3. Use the scan tool to clear the DTCs.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the text.

Does the DTC reset?

--

Go to Step 7

Go to Step 8

7

Replace the SDM.

Did you complete the replacement?

--

Go to Step 8

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8

  1. Reconnect all SIR system components.
  2. Verify that all components, connectors, and connector position assurances (CPAs) are properly mounted.
  3. Use the scan tool to clear the DTCs.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the text.

Does the DTC reset?

--

Go to Step 2

System OK