GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Blazer - 4WD - RHD 🢒 DTC 🢒 DTC B0036

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 greater than 3.65 volts for 500 milliseconds.

Action Taken When the DTC Sets

The SDM commands ON the AIR BAG warning lamp via Class 2 serial data.

Conditions for Clearing the DTC
    • The voltage at the disriminating sensor signal input is 3.65 volts or less 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 circuits 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:

  1. Tests for proper terminal contact of the yellow 2-way connector.

    2.

  2. Tests for a malfunctioning discriminating sensor.

    3.

  3. Tests for an open in the discriminating sensor ground circuit.

    4.

  4. Test isolates an open in the discriminating sensor ground circuit to one side of the in-line connector.

    5.

  5. Tests for proper terminal contact of the inflatable restraint sensing and diagnostic module (SDM) connector.

    6.

  6. Tests for an open in the discriminating sensor signal circuit.

    7.

  7. Test isolates an open in the discriminating sensor signal circuit to one side of the in-line connector.

    8.

  8. Tests for a short to voltage in the discriminating sensor signal circuit.

Step

Action

Value(s)

Yes

No

Schematic Reference: SIR Schematics

1

Did you perform the Diagnostic System Check - SIR?

--

Go to Step 2

Go to Diagnostic System Check - SIR

2

  1. Turn OFF the ignition.
  2. Disconnect the inflatable restraint front end discriminating sensor. Refer to Inflatable Restraint Front End Discriminating Sensor Replacement .
  3. Inspect for proper connection at the discriminating sensor harness connector terminals.

Do the terminals exhibit any signs of damage or corrosion?

--

Go to Step 3

Go to Step 4

3

Repair or replace the discriminating sensor harness connector. Refer to Connector Repairs in Wiring Systems.

Did you complete the replacement?

--

Go to Step 25

--

4

Check for proper connection at the discriminating sensor connector terminals.

Do the terminals exhibit any signs of damage or corrosion?

--

Go to Step 24

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the inflatable restraint front end discriminating sensor. Refer to Inflatable Restraint Front End Discriminating Sensor Replacement .
  3. UsingJ 39200 DMM measure the resistance between the discriminating sensor connector terminals. Refer to Circuit Testing in Wiring Systems.

Does the resistance measure more than the specified value?

1050 ohms

Go to Step 24

Go to Step 6

6

Using J 39200 DMM measure the resistance from the discriminating sensor harness connector terminal B to ground. Refer to Circuit Testing in Wiring Systems.

Does the resistance measure within the specified value?

0-5 ohms

Go to Step 12

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the discriminating sensor in-line harness connector.
  3. Check for proper connection at the discriminating sensor in-line harness connector terminals.

Do the terminals exhibit any signs of damage or corrosion?

--

Go to Step 8

Go to Step 9

8

Repair or replace the discriminating sensor in-line harness connector. Refer to Connector Repairs in Wiring Systems.

Did you complete the replacement?

--

Go to Step 25

--

9

Using J 39200 DMM measure the resistance between the discriminating sensor harness connector terminal B and the discriminating sensor in-line harness connector terminal B. Refer to Circuit Testing in Wiring Systems.

Does the resistance measure within the specified value?

0-5 ohms

Go to Step 10

Go to Step 11

10

Locate and repair an open in the discriminating sensor ground circuit between the in-line harness connector and the inflatable restraint sensing and diagnostic module (SDM). Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

11

Locate and repair an open in the discriminating sensor ground circuit bewteen the discriminating sensor connector and the discriminating sensor in-line harness connector. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

12

  1. Turn OFF the ignition.
  2. Disconnect the inflatable restraint sensing and diagnostic module (SDM). Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .
  3. Check for proper connection at the discriminating sensor input terminal of the inflatable restraint sensing and diagnostic module (SDM) harness connector.

Does the connector exhibit any signs of damage or corrosion?

--

Go to Step 13

Go to Step 14

13

Repair or replace the inflatable restraint sensing and diagnostic module (SDM) harness connector. Refer to Connector Repairs in Wiring Systems.

Did you complete the replacement?

--

Go to Step 25

--

14

Check for proper connection at the inflatable restraint sensing and diagnostic module (SDM) connector terminals.

Do the terminals exhibit any signs of damage or corrosion?

--

Go to Step 23

Go to Step 15

15

  1. Disable the SIR system. Refer to Disabling the SIR System .
  2. Using J 39200 DMM measure the resistance between the discriminating sensor harness connector terminal A and the inflatable restraint sensing and diagnostic module (SDM) harness connector terminal A11. Refer to Circuit Testing in Wiring Systems.

Does the resistance measure within the specified value?

0-5 ohms

Go to Step 21

Go to Step 16

16
  1. Disconnect the discriminating sensor in-line harness connector.
  2. Check for proper connection of the discriminating sensor input circuit at the discriminating sensor in-line harness connector.

Do the terminals exhibit any signs of damage or corrosion?

--

Go to Step 17

Go to Step 18

17

Repair or replace the discriminating sensor in-line harness connector. Refer to Connector Repairs in Wiring Systems.

Did you complete the replacement?

--

Go to Step 25

--

18

Using J 39200 DMM measure the resistance of the discriminating sensor input circuit between the discriminating sensor harness connector and the discriminating sensor in-line harness connector. Refer to Circuit Testing in Wiring Systems.

Does the resistance measure within the specified value?

0-5 ohms

Go to Step 19

Go to Step 20

19

Locate and repair an open 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 25

--

20

Locate and repair an open 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 25

--

21

  1. Install the AIR BAG Fuse.
  2. Turn ON the ignition, with the engine OFF.
  3. Using J 39200 DMM measure the voltage of the discriminating sensor input circuit at the discriminating sensor harness connector to ground. Refer to Circuit Testing in Wiring Systems.

Does the voltage measure less than the specified value?

1.0 V

Go to Diagnostic System Check - SIR

Go to Step 22

22
  1. Turn OFF the ignition.
  2. Remove the AIR BAG Fuse.
  3. Locate and repair a short to voltage in the discriminating sensor input circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

23

Replace the inflatable restraint sensing and diagnostic module (SDM). Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .

Did you complete the replacement?

--

Go to Step 25

--

24

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 25

--

25
  1. Reconnect all SIR system components.
  2. Verify that all components, connectors, and CPAs are properly mounted.
  3. Use the scan tool in order to clear the DTCs.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK