GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2007 🢒 Rendezvous - FWD 🢒 DTC 🢒 DTC B1440
Table 1: Correct Power Mode Inputs
Table 2: Incorrect Power Mode 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. There are 3 discrete wires from the ignition switch contacts monitored by the BCM 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 BCM power mode data:

Correct Power Mode Inputs

Ignition Switch Position

BCM Input and Scan Tool Display

Ignition 0

Ignition 1

Ignition Accessory

OFF and LOCK

Inactive

Inactive

Inactive

ACC

Active

Inactive

Active

ON

Active

Active

Active

CRANK

Active

Active

Inactive

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1440 Power Mode Master Input Circuits Mismatch

Conditions for Setting the DTC

One of the 3 monitored ignition switch circuits has malfunctioned. Refer to the following example:

Incorrect Power Mode Inputs

Ignition Switch Position

BCM Input and Scan Tool Display

Ignition 0

Ignition 1

Ignition Accessory

OFF and LOCK

Inactive

Active

Inactive

ACC

Active

Inactive

Inactive

ON

Active

Active

Inactive

CRANK

Inactive

Active

Active

Action Taken When the DTC Sets
    • The BCM implements default actions for each ignition switch position when faults are detected.
    • The Service Engine Soon (SES) Light will illuminate.

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: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install a scan tool.
  2. Turn the ignition switch to OFF.
  3. With a scan tool, monitor the following in body control module (BCM), Data Display, Inputs:
    4. • Ignition 0
    • Ignition 1
    • Ignition Accessory

Does the scan tool match the power mode table for the current ignition switch position?

Go to Step 3

Go to Step 7

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 match the power mode table for the current ignition switch position?

Go to Step 4

Go to Step 9

4
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  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 match the power mode table for the current ignition switch position?

Go to Step 5

Go to Step 9

5

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

  1. Install a scan tool.
  2. Turn the ignition switch to START.
  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 match the power mode table for the current ignition switch position?

Go to Step 6

Go to Step 9

6

Were any of the ignition switch inputs active when they were not called for in the previous steps?

Go to Step 7

Go to Step 12

7
  1. Disconnect the ignition switch harness connectors.
  2. Install a scan tool.
  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 any of the Ignition 0, Ignition 1 or Ignition Accessory inputs are active?

Go to Step 8

Go to Step 10

8
  1. Disconnect the BCM harness connectors.
  2. Test the suspect ignition switch input circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 15

Go to Step 12

9
  1. Disconnect the ignition switch connectors.
  2. Install a 3-amp 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?

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.

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 suspect ignition switch input circuits for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs .

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.

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 .

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?

System OK

Go to Step 2