GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Classic 🢒 DTC 🢒 DTC B1374

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. If the BCM senses that ignition 0 and 3 are active and ignition 1 is inactive while the engine is running, DTC B1374 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1374 Device Ignition 1 (ON and START) 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 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 B1374 will clear when the ignition switch is cycled, and the code setting condition is no longer present.
    • 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 step numbers on the diagnostic table.

  1. This step determines if the ignition 1 circuit is shorted to ground.

    2.

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

    3.

  3. 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 1 INPUT data parameter in the body control module (BCM) data list.

Does the scan tool display ACTIVE?

Go to Step 10

Go to Step 3

3

Inspect the A/C BFC fuse.

Is the fuse open?

Go to Step 4

Go to Step 6

4

  1. Connect a test lamp between the A/C BFC fuse terminals at the junction block-underhood.
  2. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

Go to Step 5

Go to Testing for Electrical Intermittents in Wiring Systems

5

  1. Turn OFF the ignition.
  2. Disconnect the connector from the BCM that contains the ignition 1 circuit.
  3. Turn ON the ignition, with the engine OFF.

Does the test lamp still illuminate?

Go to Step 8

Go to Step 10

6

  1. Remove the A/C BFC fuse.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe both fuse terminals for the ignition 1 positive voltage circuit at the junction block-underhood with a test lamp connected to ground.

Does the test lamp illuminate for one of the terminals?

Go to Step 7

Go to Step 9

7

Test the ignition 1 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 12

Go to Step 11

8

Repair the short to ground in the ignition 1 positive voltage circuit. Refer to Wiring Repairs in Wiring Systems for the proper procedure and Body Control System Schematics for the circuit ID's.

Did you complete the repair?

Go to Step 12

--

9

Repair the open in the ignition feed circuit to the A/C BFC fuse. Refer to Wiring Repairs in Wiring Systems.

Did you complete the action?

Go to Step 12

--

10
  1. Inspect for poor connections at the harness connector of the BCM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  2. Inspect entire ignition 1 circuit path for intermittent connection. Refer to Testing for Intermittent Conditions and Poor Connections and Power Distribution Schematics in Wiring Systems for the proper procedure and circuit IDs.

Did you find and correct the condition?

Go to Step 12

Go to Step 11

11

Replace the BCM. Refer to Control Module References .

Did you complete the replacement?

Go to Step 12

--

12
  1. Use the Scan Tool in order to clear the DTCs.
  2. 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