GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Classic 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 DTC B1379

Circuit Description

The body control module (BCM) uses the ignition 0, ignition 1, and ignition 3 inputs to determine the power mode of the vehicle. The BCM may store a DTC if it detects an invalid combination of ignition input signals. When the BCM senses that the ignition 1 input is active and ignition 3 is inactive while the engine is running, DTC B1379 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1379 Device Ignition 3 (ON) Circuit Open

Conditions for Running the DTC

The engine has been running for at least 20  seconds.

Conditions for Setting the DTC

The ignition 1 input is active and ignition 3 is inactive

Action Taken When the DTC Sets
    • The SERVICE VEHICLE SOON indicator illuminates.
    • The check gages chime sounds.

Conditions for Clearing the DTC
    • A current DTC B1379 will clear when the malfunction is no longer present and the ignition switch is cycled.
    • A history DTC clears when the ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while wiggling the wiring and connectors. This can often cause the malfunction to appear.

Test Description

The numbers below refer to the numbers on the diagnostic table.

  1. This step determines if ignition 3 is shorted to ground.

    2.

  2. This step determines if the BCM is internally shorted.

    3.

  3. This step determines if the cruise control module is internally shorted.

    4.

  4. This step determines if voltage is supplied from the battery to the fuse.

Step

Action

Yes

No

Schematic Reference: Body Control System Schematics

Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems.

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, observe the IGNITION 3 INPUT data parameter in the body control module (BCM) data list.

Does the scan tool display ACTIVE?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Inspect the CRUISE fuse.

Is the fuse open?

Go to Step 4

Go to Step 7

4

  1. Connect a test lamp between the CRUISE fuse terminals at the Fuse Block-Right I/P.
  2. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

Go to Step  5

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

5

  1. Turn OFF the ignition.
  2. Disconnect the connector from the BCM that contains ignition 3. Refer to Body Control System Schematics for the appropriate connector and circuit IDs.
  3. Turn ON the ignition, with the engine OFF.

Does the test lamp still illuminate?

Go to Step 6

Go to Step 11

6

  1. Turn OFF the ignition.
  2. Disconnect the cruise control module connector.
  3. Turn ON the ignition, with the engine OFF.

Does the test lamp still illuminate?

Go to Step 9

Go to Step 12

7

  1. Remove the CRUISE fuse.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe both fuse terminals for the ignition 3 positive voltage circuit at the Fuse Block-Right I/P with a test lamp connected to a good ground.

Does the test lamp illuminate for one of the circuits?

Go to Step  8

Go to Step 10

8

Test the ignition 3 positive voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 13

9

Repair the short to ground in the ignition 3 positive voltage circuit. Refer to Wiring Repairs in Wiring Systems for the proper procedure and Body Control System Schematics for the circuit IDs.

Did you complete the action?

Go to Step 15

--

10

Repair the open in the ignition feed circuit to the CRUISE fuse. Refer to Wiring Repairs in Wiring Systems.

Did you complete the action?

Go to Step 15

--

11

Inspect for poor connections at the harness of the BCM that contains the ignition 3 circuit. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems and Body Control System Schematics for the connector and circuit IDs.

Did you find and correct the condition?

Go to Step 15

Go to Step 13

12

Inspect for poor connections at the harness connector of the cruise control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems for the proper procedure.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

13

Replace the BCM. Refer to Control Module References .

Did you complete the repair?

Go to Step 15

--

14

Replace the cruise control module. Refer to Control Module References .

Did you complete the repair?

Go to Step 15

--

15
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Condition for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK