GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 Equinox 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 DTC B1377 or B1378
Table 1: Correct Ignition Switch Input Signals

Circuit Description

The body control module (BCM) is the power mode master responsible for sending the power mode message on the data buses. The BCM monitors Ignition 1 (Run/Crank), Ignition 2 (Acc/Run) and Ignition 3 (Run) signals from the ignition switch, and the engine run flag (ERF) in order to determine the present power mode. The following table represents correct BCM input signals corresponding to each ignition switch position.

Correct Ignition Switch Input Signals

Ignition Switch Position

BCM Input and Scan Tool Display

Ignition 1 (Run/Crank)

Ignition 2 (Acc/Run)

Ignition 3 (Run)

OFF

Low

Low

Inactive

ACC

Low

High

Inactive

ON

High

High

Active

START

High

Low

Inactive

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC B1377 Device Ignition 3 (ON) Circuit Low
    • DTC B1378 Device Ignition 3 (ON) Circuit High

Conditions for Running the DTC

The only requirements are voltage and ground.

Conditions for Setting the DTC

The following table describes the setting of the DTCs.

Engine Running (ERF)

BCM Inputs

DTC Set

Ignition 1 (Run/Crank)

Ignition 2 (Acc/Run)

Ignition 3 (Run)

no

Low

Low

Active

B1378

no

High

Low

Active

B1382¹

no

High

High

Inactive

B1377¹

no

Low

High

Active

B1372¹

yes

Low

Low

Inactive

B1372¹, B1377¹ and B1382¹

yes

High

Low

Inactive

B1377¹ and B1382¹

yes

Low

Low

Active

B1372 and B1382

yes

High

Low

Active

B1382¹

yes

Low

High

Inactive

B1372¹ and B1377¹

yes

High

High

Inactive

B1377¹

yes

Low

High

Active

B1372¹

¹ The module sets the DTC 1 minute after it detects the condition.

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

Step

Action

Yes

No

Schematic Reference: Body Control System Schematics

Connector End View Reference: Computer/Integrating Systems Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Did you record only the DTC B1377?

Go to Step 3

Go to Step 4

3
  1. Disconnect the ignition switch connector.
  2. Test the battery voltage circuit to the cavity A of the ignition switch for a short to ground or 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 9

4
  1. Install a scan tool.
  2. Turn the ignition switch to OFF.
  3. With a scan tool, monitor the Ignition 3 Input of the BCM, under Security Data.

Does the scan tool indicate that the Ignition 3 Input is inactive?

Go to Step 5

Go to Step 7

5
  1. Turn the ignition switch to ACC.
  2. With a scan tool, monitor the Ignition 3 Input of the BCM, under Security Data.

Does the scan tool indicate that the Ignition 3 Input is inactive?

Go to Step 6

Go to Step 7

6

Important: The engine may start in this step. Turn the engine OFF immediately after reviewing the input data.

  1. Turn the ignition switch to START.
  2. With a scan tool, monitor the Ignition 3 Input of the BCM, under Security Data.

Does the scan tool indicate that the Ignition 3 Input is inactive?

Go to Step 8

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the ignition switch connectors.
  3. Test the body control module (BCM) ignition switch input circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  4. Test the BCM ignition switch input circuits for a short between circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 10

8
  1. Turn the ignition switch to RUN.
  2. With a scan tool, monitor the Ignition 3 Input of the BCM, under Security Data.

Does the scan tool indicate that the Ignition 3 Input is active?

Go to Step 12

Go to Step 9

9
  1. Turn OFF the ignition.
  2. Disconnect the ignition switch connectors.
  3. Install a 3A fused jumper between the Ignition 3 input circuit and an ignition switch B+ supply.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, monitor the Ignition 3 Input of the BCM, under Security Data.

Does the scan tool indicate that the Ignition 3 Input circuit is now active?

Go to Step 10

Go to Step 11

10

Inspect for poor connections at the ignition switch harness connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 13

11
  1. Disconnect the BCM harness connectors.
  2. Test the Ignition 3 input circuit for a short to ground or 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 12

12

Inspect for poor connections at the BCM harness connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

13

Replace the ignition switch. Refer to Ignition and Start Switch Replacement in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 15

--

14

Replace the BCM. Refer to Control Module References for replacement, setup and programming.

Did you complete the replacement?

Go to Step 15

--

15
  1. Reconnect all components.
  2. Use the scan tool in order to clear DTCs.
  3. 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