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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Chevy C Silverado - 2WD 🢒 Restraints 🢒 SIR 🢒 DTC B1021 Driver Deployment Loop Resistance High

Object Number: 398018 Size: SF
SIR Components
SIR Schematics
SIR Schematic Icons
SIR Schematic Icons

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 the SDM. Next the SDM measures Ignition Positive Voltage 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 performs the following steps:

    • 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:
       - The inflatable restraint steering wheel module
       - The inflatable restraint steering wheel module coil
       - The harness wiring of CKT 347
       - The harness wiring of CKT 348
       - The connector terminal contact

The RESISTANCE MEASUREMENT test inspects for this malfunction. This test only occurs once each ignition cycle when Ignition Positive Voltage is within the normal operating voltage range.

Action Taken When the DTC Sets
    • The SDM sets a diagnostic trouble code.
    • 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.
       - After 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 may cause an intermittent condition. Inspect the following for a poor connection:

    • The inflatable restraint steering wheel module steering column connector terminals A and B
    • The upper inflatable restraint steering wheel module coil connector terminals A and B
    • The SDM terminals 2 and 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 may 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 test determines the deployment loop resistance measured by the inflatable restraint sensing and diagnostic module (SDM).

    2.

  2. This test checks for proper contact or corrosion of the yellow 2-way connector.

    3.

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

    4.

  4. This test determines whether the malfunction is due to the inflatable restraint steering wheel module or the module coil.

    5.

  5. This test checks for proper contact or corrosion of the SDM connector.

    6.

  6. This test determines whether the malfunction is in CKT 347.

    7.

  7. This test determines whether the malfunction is in CKT 348.

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. Connect the Scan Tool to the DLC.
  3. Turn the ignition switch to the RUN position.
  4. Request the SIR data list display.
  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 and IP module yellow 2-way connectors near the base of the steering column and behind the glove box.
  3. Inspect for proper connection at terminals A and B on the harness side of the inflatable restraint steering wheel module yellow 2-way connector at the base of the steering column.

Are the terminals damaged or corroded?

--

Go to Step 4

Go to Step 6

4

Replace the yellow 2-way harness connector at the base of the steering column. Refer to Wiring Repair .

Is the repair complete?

--

Go to Step 5

--

5

Inspect for proper connection at terminals A and B of the inflatable restraint steering wheel module coil side of the connector.

Are the terminals damaged or corroded?

--

Go to Step 7

Go to Step 23

6

Inspect for proper connection at terminals A and B of the inflatable restraint steering wheel module coil side of the connector.

Are the terminals damaged or corroded?

--

Go to Step 7

Go to Step 8

7

Replace the inflatable restraint IP 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 and IP module yellow 2-way connectors near the base of the steering column and behind the glove box.
  2. Turn the ignition switch to the RUN position.
  3. Using the Scan Tool , request the SIR data list display.
  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 yellow 2-way harness connector at the base of the steering column. 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 and IP module yellow 2-way connectors near the base of the steering column and behind the glove box.
  3. Connect J 38715-A SIR Driver/Passenger Load Tool to the harness connectors.
  4. Turn the ignition switch to the RUN position.
  5. Using the Scan Tool , request the data list display.
  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 J 38715-A from the driver 2-way connector.
  4. Connect the 2-way connector.
  5. Connect 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. Using the Scan Tool , request the SIR data list display.
  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 SDM. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .
  3. Disconnect the J 38715-A .
  4. Inspect for proper connection at terminal 2 and terminal 3 on the harness side of the SDM connector.

Is the connector damaged or corroded?

--

Go to Step 15

Go to Step 17

15

Replace the SDM harness connector. Refer to Wiring Repair .

Is the repair complete?

--

Go to Step 16

--

16

Inspect for proper connection at terminal 2 and terminal 3 on the SDM.

Are the terminals damaged or corroded?

--

Go to Step 18

Go to Step 23

17

Inspect for proper connection at terminal 2 and terminal 3 on the SDM.

Are the 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.
  2. Measure the resistance from the SDM harness connector terminal 2 to the inflatable restraint steering wheel module yellow 2-way harness connector terminal A.

Is the resistance reading within the specified values?

0-0.5 ohms

Go to Step 21

Go to Step 20

20

Repair the high resistance condition in CKT 347.

Is the repair complete?

--

Go to Step 23

--

21

Measure the resistance from the SDM harness connector terminal 3 to the inflatable restraint steering wheel module yellow 2-way harness connector terminal B.

Is the resistance reading within the specified values?

0-0.5 ohms

Go to Sensing and Diagnostic Module Integrity Check

Go to Step 22

22

Repair the high resistance condition in CKT 348.

Is the repair complete?

--

Go to Step 23

--

23
  1. Reconnect all the SIR system components.
  2. Ensure that all of the components are properly mounted.

Have all the SIR components been reconnected and properly mounted?

--

Go to Step 24

--

24

Clear all the SIR DTCs.

Have all the SIR DTCs been cleared?

--

Go to SIR Diagnostic System Check

--