GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Monte Carlo 🢒 DTC 🢒 DTC B1021 Driver Deployment Loop Resistance High

Object Number: 420623 Size: SF
SIR Components
Cell 47: SIR Diagnostic Module, Seat Belt Switch
SIR Caution
Handling ESD Sensitive Parts Notice

Circuit Description

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. Next the SDM measures IGNITION 1 and the deployment loop voltages to make sure they are within their respective normal voltage ranges. Then the SDM proceeds with the RESISTANCE MEASUREMENT test. During one portion of the RESISTANCE MEASUREMENT test, the SDM does the following:

    • Grounds the DRIVER SIDE LOW terminal 3 through an internal current sink.
    • Connects the DRIVER SIDE HIGH terminal 2 to an internal constant current source. This current produces proportional voltage drops in the deployment loop.
    • Measures the voltage difference between DRIVER SIDE HIGH and DRIVER SIDE LOW.
    • Calculates the resistance of the driver deployment loop using the measured voltage.

Conditions for Setting the DTC

    • The driver and passenger deployment loops are not open.
    • The driver and passenger deployment loops are not shorted to voltage.
    • The driver deployment loop is not shorted to ground.
    • The driver deployment loop resistance is more than 3.8 ohms. The driver deployment loop consists of the following components:
       - Inflatable restraint steering wheel module.
       - Inflatable restraint steering wheel module coil.
       - Harness wiring of CKT 347.
       - Harness wiring of CKT 348.
       - Connector terminal contact.

The RESISTANCE MEASUREMENT test checks for this malfunction. This test only occurs once each ignition cycle when IGNITION 1 is within the normal operating voltage range.

Action Taken When the DTC Sets
    • The SDM sets a DTC B1021.
    • The SDM turns ON the AIR BAG warning lamp.

Conditions for Clearing the DTC

The DTC will clear when one of the following conditions is met:

    • Current DTC
        The resistance of the driver deployment loop is less than 3.8 ohms and the ignition switch is cycled.
    • History DTC
       - You issue a scan tool CLEAR CODES command.
       - Once 250 malfunction free ignition cycles have occurred.

When you issue a scan tool CLEAR CODES command and the malfunction is still present, the DTC will not reappear until the next ignition cycle.

Diagnostic Aids

A poor connection can cause an intermittent condition. Check the following for a poor connection:

    • The inflatable restraint steering wheel module coil connector terminal A and terminal B.
    • The upper inflatable restraint steering wheel module coil connector terminal A and terminal B.
    • The SDM wiring harness connector terminal 2 and terminal 3.
    • The wire to terminal connections in CKT 347.
    • The wire to terminal connections in CKT 348.

The diagnostic table directs the technician to note the entry value of DRIVER RESISTANCE. Comparing the value of DRIVER RESISTANCE over multiple ignition cycles can be helpful in determining if an intermittent condition exists.

When measurements are requested in this table, use the J 39200 DMM with the correct terminal adapter from the J 35616 Connector Test Adapter Kit. When an inspection for proper connection is requested, refer to Testing for Electrical Intermittents in Wiring Systems. When a wire, connector or terminal repair is requested, use the J-38125 Terminal Repair Kit and refer to Wiring Repairs in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table:

  1. This step checks the driver deployment loop resistance that was measured by the inflatable restraint sensing and diagnostic module (SDM).

    2.

  2. This step checks to see if the inflatable restraint steering wheel module yellow 2-way connector is corroded or damaged.

    3.

  3. This step isolates the malfunction to one side of the inflatable restraint steering wheel module yellow 2-way connector.

    4.

  4. This step determines if there is a malfunctioning inflatable restraint steering wheel module coil or if there is a malfunctioning inflatable restraint steering wheel module.

    5.

  5. This step checks the SDM wiring harness connector for corrosion or damaged terminals.

    6.

  6. This step checks to see if there is a high resistance in CKT 347.

    7.

  7. This step determines if there is a high resistance in CKT 348 or if there is a malfunctioning SDM.

DTC B1021 Driver Deployment Loop Resistance High

Step

Action

Value(s)

Yes

No

1

Was the SIR Diagnostic System Check performed?

--

Go to Step 2

Go to SIR Diagnostic System Check

2

  1. Turn the ignition switch to the OFF position.
  2. Install the scan tool.
  3. Turn the ignition switch to the RUN position.
  4. Use the scan tool to request the SIR scan tool data list.
  5. Read and record on the repair order the driver deployment loop resistance DRIVER RESISTANCE.

Has the DRIVER RESISTANCE been read and recorded on the repair order?

--

Go to Step 3

--

3

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the inflatable restraint steering wheel module coil and IP module yellow 2-way wiring harness connectors.
  3. Check for a proper connection at terminal A and terminal B on the IP wiring harness side of the inflatable restraint steering wheel module coil yellow 2-way wiring harness connector.

Are the terminals damaged or corroded?

--

Go to Step 4

Go to Step 6

4

Replace the inflatable restraint steering wheel module coil yellow 2-way wiring harness connector. Refer to Wiring Repair .

Is the repair complete?

--

Go to Step 5

--

5

Check for a proper connection at terminal A and terminal B of the inflatable restraint steering wheel module coil yellow 2-way connector.

Are the terminals damaged or corroded?

--

Go to Step 7

Go to Step 23

6

Check for a proper connection at terminal A and terminal B of the inflatable restraint steering wheel module coil yellow 2-way connector.

Are the terminals damaged or corroded?

--

Go to Step 7

Go to Step 8

7

Replace the inflatable restraint steering wheel module coil. Refer to Inflatable Restraint Steering Wheel Module Coil Replacement .

Is the repair complete?

--

Go to Step 23

--

8
  1. Connect the inflatable restraint steering wheel module coil and IP module yellow 2-way wiring harness connectors.
  2. Turn the ignition switch to the RUN position.
  3. Use the scan tool to request the SIR scan tool data list.
  4. Read the driver deployment loop resistance DRIVER RESISTANCE.

Is DRIVER RESISTANCE more than the specified value?

3.8 ohms

Go to Step 10

Go to Step 9

9
  1. Turn the ignition switch to the OFF position.
  2. Replace the inflatable restraint steering wheel module coil yellow 2-way wiring harness connector. Refer to Wiring Repair .

Is the repair complete?

--

Go to Step 23

--

10

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the inflatable restraint steering wheel module coil and IP module yellow 2-way wiring harness connectors.
  3. Connect the J 38715-A SIR Driver/Passenger Load Tool to the IP wiring harness connectors.
  4. Turn the ignition switch to the RUN position.
  5. Use the scan tool to request the SIR scan tool data list.
  6. Read the driver deployment loop resistance DRIVER RESISTANCE.

Is DRIVER RESISTANCE more than the specified value?

3.8 ohms

Go to Step 14

Go to Step 11

11

  1. Turn the ignition switch to the OFF position.
  2. Remove the inflatable restraint steering wheel module. Refer to Inflatable Restraint Steering Wheel Module Replacement .
  3. Disconnect the J 38715-A from the inflatable restraint steering wheel module coil yellow 2-way wiring harness connector.
  4. Connect the inflatable restraint steering wheel module coil yellow 2-way wiring harness connector.
  5. Connect the J 38715-A to the upper inflatable restraint steering wheel module coil connector on the steering column.
  6. Turn the ignition switch to the RUN position.
  7. Use the scan tool to request the SIR scan tool data list.
  8. Read the driver deployment loop resistance DRIVER RESISTANCE.

Is DRIVER RESISTANCE more than the specified value?

3.8 ohms

Go to Step 13

Go to Step 12

12
  1. Turn the ignition switch to the OFF position.
  2. Replace the inflatable restraint steering wheel module. Refer to Inflatable Restraint Steering Wheel Module Replacement .

Is the repair complete?

--

Go to Step 23

--

13
  1. Turn the ignition switch to the OFF position.
  2. Replace the inflatable restraint steering wheel module coil. Refer to Inflatable Restraint Steering Wheel Module Coil Replacement .

Is the repair complete?

--

Go to Step 23

--

14

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the inflatable restraint sensing and diagnostic module (SDM). Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .
  3. Remove the J 38715-A from the IP wiring harness connectors.
  4. Check for a proper connection at terminal 2 and terminal 3 of the SDM wiring harness connector.

Is the SDM wiring harness connector damaged or corroded?

--

Go to Step 15

Go to Step 17

15

Replace the SDM wiring harness connector. Refer to Wiring Repair .

Is the repair complete?

--

Go to Step 16

--

16

Check for a proper connection at terminal 2 and terminal 3 of the SDM.

Are the SDM terminals damaged or corroded?

--

Go to Step 18

Go to Step 23

17

Check for a proper connection at terminal 2 and terminal 3 of the SDM.

Are the SDM terminals damaged or corroded?

--

Go to Step 18

Go to Step 19

18

Replace the SDM. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .

Is the repair complete?

--

Go to Step 23

--

19

  1. Zero the J 39200 Digital Multimeter (DMM).
  2. Use the J 39200 to measure the resistance between terminal 2 of the SDM wiring harness connector and terminal A of the inflatable restraint steering wheel module coil yellow 2-way wiring harness connector.

Is the measured resistance within the specified value?

0-0.5 ohms

Go to Step 21

Go to Step 20

20
  1. Locate a high resistance in CKT 347.
  2. Repair the high resistance in CKT 347.

Is the repair complete?

--

Go to Step 23

--

21

Use the J 39200 to measure the resistance between terminal 3 of the SDM wiring harness connector and terminal B of the inflatable restraint steering wheel module coil yellow 2-way wiring harness connector.

Is the measured resistance within the specified value?

0-0.5 ohms

Go to Sensing and Diagnostic Module Integrity Check

Go to Step 22

22
  1. Locate a high resistance in CKT 348.
  2. Repair the high resistance in CKT 348.

Is the repair complete?

--

Go to Step 23

--

23

Reconnect all the SIR system components, making sure all the components are properly mounted.

Have all the SIR components been reconnected and properly mounted?

--

Go to Step 24

--

24

Use the scan tool to clear all current and history SIR DTCs.

Have all current and history SIR DTCs been cleared?

--

Go to SIR Diagnostic System Check

--