GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Tahoe - 2WD 🢒 DTC 🢒 DTC B1440
Table 1: Correct Ignition Switch Inputs
Table 2: Incorrect Ignition Switch Inputs

Circuit Description

The body control module (BCM) is the power mode master responsible for sending ignition switch position information on the class 2 serial data link. The BCM monitors 3 discrete wires from the ignition switch contacts and the engine run flag (ERF) in order to determine the present power mode. The BCM communicates this power mode information to all class 2 modules on the class 2 serial data link. The following table represents correct BCM power mode data:

Correct Ignition Switch Inputs

Ignition Switch Position

BCM Input and Scan Tool Display

Ignition Accessory

Ignition 1

Ignition 0

OFF

Inactive

Off

Off

UNLOCK

Inactive

Off

On

ACC

Active

Off

On

ON

Active

On

On

START

Inactive

On

On

Conditions for Running the DTC

The only requirements are voltage and ground.

Conditions for Setting the DTC

One of the 3 monitored ignition switch circuits has malfunctioned. The DTC will set, if one of the following situations is present:

Incorrect Ignition Switch Inputs

BCM Input and Scan Tool Display

Engine Running

Ignition Accessory

Ignition 1

Ignition 0

Inactive

On

Off

No

Active

Off

Off

No

Active

On

Off

No

Inactive

On

Off

Yes

Inactive¹

On

On

Yes

Active

Off

Off

Yes

Active

Off

On

Yes

Active

On

Off

Yes

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

Action Taken When the DTC Sets

The BCM implements default actions for each ignition switch position when faults are detected.

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: Body Control System Connector End Views

1

Perform the Diagnostic System Check for the system exhibiting the symptom. Refer to Control Module References .

Did you perform the Diagnostic System Check?

Go to Step 2

Go to Control Module References

2
  1. Install a scan tool.
  2. Turn OFF the ignition.
  3. With a scan tool, monitor the following in Body Control Module, Data Display, Inputs:
    4. • Ignition 0
    • Ignition 1
    • Ignition Accessory

Does the scan tool indicate that all inputs are inactive/Off?

Go to Step 3

Go to Step 6

3
  1. Install a scan tool.
  2. Turn the ignition switch to ACC.
  3. With a scan tool, monitor the following in Body Control Module, Data Display, Inputs:
    4. • Ignition 0
    • Ignition 1
    • Ignition Accessory

Does the scan tool indicate that the Ignition 0 and Ignition Accessory inputs are active/On?

Go to Step 4

Go to Step 8

4
  1. Turn the ignition switch ON, with the engine OFF.
  2. With a scan tool, monitor the following in Body Control Module, Data Display, Inputs:
    3. • Ignition 0
    • Ignition 1
    • Ignition Accessory

Does the scan tool indicate that the all inputs are active/On?

Go to Step 5

Go to Step 8

5

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 following in Body Control Module, Data Display, Inputs:
    3. • Ignition 0
    • Ignition 1
    • Ignition Accessory

Does the scan tool indicate that the Ignition 0 and Ignition 1 inputs are On and the Ignition Accessory input is inactive?

Go to Step 11

Go to Step 8

6
  1. Disconnect the ignition switch harness connectors.
  2. With a scan tool, monitor the following in Body Control Module, Data Display, Inputs:
    3. • Ignition 0
    • Ignition 1
    • Ignition Accessory

Does the scan tool indicate that any of the Ignition 0, Ignition 1 or Ignition Accessory inputs is active/On?

Go to Step 7

Go to Step 9

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

Did you find and correct the condition?

Go to Step 14

Go to Step 11

8
  1. Disconnect the ignition switch connectors.
  2. Install a 3A fused jumper between the suspect circuits and an ignition switch B+ supply.
  3. With a scan tool, monitor the suspect circuits in Body Control Module, Data Display, Inputs:
    4. • Ignition 0
    • Ignition 1
    • Ignition Accessory

Does the scan tool indicate that the suspect circuits are now active/On?

Go to Step 9

Go to Step 10

9

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 14

Go to Step 12

10
  1. Disconnect the BCM harness connectors.
  2. Test the suspect ignition switch input circuits 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 14

Go to Step 11

11

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 14

Go to Step 13

12

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

Did you complete the replacement?

Go to Step 14

--

13

Important: Perform the programming or setup procedure for the module, if required.

Replace the BCM. Refer to Body Control Module Replacement .

Did you complete the replacement?

Go to Step 14

--

14
  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