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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 XLR 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC B1451

Circuit Description

The body control module (BCM) provides an accessory voltage output, enabled in Run and Accessory power modes. The accessory voltage circuit provides power for engine control module (ECM), transmission control module (TCM), and wiper run/acc relay.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1451 Accessory Power Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC Symptom

DTC Symptom Descriptor

02

Short to ground

05

Short to battery or open

Conditions for Running the DTC

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

Conditions for Setting the DTC

B1451 02

    • The BCM detects a short to ground in the accessory power circuit when the output is active.
    • The condition above must be present for more than 5 seconds.

B1451 05

    • The BCM detects a short to battery or an open in the accessory power circuit when the output is inactive.
    • The condition above must be present for more than 1 second.

Action Taken When the DTC Sets

The BCM will disable the accessory power output until the next ignition cycle.

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.

Diagnostic Aids

If the DTC B1451 02 or B1451 05 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .

The following conditions may cause DTC to occur:

    • A short to ground, a short to battery or an open in the accessory power circuit.
    • A fault in one of the following modules that shorts the circuit to ground or battery:
       - ECM
       - TCM
    • An internal wiper run/acc relay fault.
    • An internal BCM fault.

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 ON the ignition, with the engine OFF.
  3. Retrieve and record DTCs.

Does the DTC set as current?

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Disconnect the wiper run/acc relay.
  3. Connect a test lamp across the relay coil circuits of the wiper run/acc relay.
  4. Turn the ignition ON, with the engine OFF.
  5. Retrieve DTCs from body control module (BCM).

Does the DTC set as current?

Go to Step 4

Go to Step 7

4

Did the test lamp illuminate in the previous step?

Go to Step 8

Go to Step 5

5

Connect the test lamp between the positive side of the wiper run/acc relay and a good ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 8

6

Repair the ground circuit of the wiper run/acc relay for an open. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 15

--

7

Replace the wiper run/acc relay.

Did you complete the repair?

Go to Step 15

--

8
  1. Turn OFF the ignition.
  2. Disconnect the following connectors/devices:
    3. • Engine control module (ECM)
    • Transmission control module (TCM)
  3. Turn the ignition ON, with the engine OFF.
  4. Retrieve DTCs from BCM.

Does the DTC set as current?

Go to Step 9

Go to Step 12

9
  1. Turn the ignition OFF.
  2. Disconnect the BCM.
  3. Test the accessory voltage circuit for an open, a short to ground or a short to voltage. Refer to Wiring Repairs and Circuit Testing .

Did you find and correct the condition?

Go to Step 15

Go to Step 10

10

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

Did you find and correct the condition?

Go to Step 15

Go to Step 11

11

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

Did you complete the replacement?

Go to Step 11

--

12

Important: Repeat this step until the condition is found.

Reconnect each previously disconnected device from step 8 one at a time to detect what device pulls the circuit low or high.

  1. Turn the ignition OFF.
  2. Reconnect a previously disconnected device.
  3. Turn the ignition ON, with the engine OFF.
  4. Retrieve DTCs from BCM.

Does the DTC set as current?

Go to Step 13

--

13

Inspect for poor connections at the harness connectors of the most recently connected device. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs .

Did you find and correct the condition?

Go to Step 15

Go to Step 14

14

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

Did you complete the replacement?

Go to Step 15

--

15
  1. Reconnect all of the disconnected modules.
  2. Use the scan tool in order to clear the DTCs.
  3. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

Go to Step 2

System OK