GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2006 🢒 Terraza Ext. 🢒 Brakes 🢒 Park Brake 🢒 DTC B1428

Circuit Description

The body control module (BCM) controls the IGN MAIN relay. The contacts of the IGN MAIN relay deliver a B+ signal to the following components:

    • The antilock brake system (ABS) functions
    • The AC compressor relay
    • The crank relay
    • The HVAC control head
    • The instrument panel cluster (IPC)
    • The powertrain control module (PCM)
    • The sensing and diagnostic module (SDM)
    • The transmission solenoids

The BCM will energize the IGN MAIN relay when the vehicle is in the RUN or CRANK power mode. The BCM supplies a B+ signal to the relays control circuit to energize it. The relays control circuit receives it's ground from G113. If a short or circuit malfunction takes place in the IGN MAIN control circuit the BCM will set a B1428 and the relay will not energize.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1428 Ignition-Switched Power Relay Circuit

Conditions for Running the DTC

The ignition switch is in the RUN or CRANK position.

Conditions for Setting the DTC
    • A DTC B1428 sets when the BCM detects a short to ground in the IGN MAIN relay control feed circuit when it is trying to energize the IGN MAIN relay.
    • A DTC B1428 sets when the BCM detects an open in the IGN MAIN relay control feed circuit when it is trying to energize the IGN MAIN relay.
    • The conditions above must be present for more than 0.3 second.

Action Taken When the DTC Sets

The BCM stores DTC B1428 in memory.

Conditions for Clearing the DTC
    • A short to ground or a malfunction in the IGN MAIN relay control feed circuit is no longer detected by the BCM.
    • A history DTC B1428 will clear after the modules ignition counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids
    • If the DTC B1428 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .
    • The following conditions may cause an intermittent malfunction to occur:
       - An intermittent short to ground in the IGN MAIN relay control feed circuit
       - The IGN MAIN relay coil is shorted to ground internally
       - The BCM is shorted to ground internally

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Listen for an audible click when the IGN MAIN relay operates. Command both the ON and OFF states. Repeat the commands, as necessary.

    2.

  2. This step verifies that the BCM is providing voltage to the IGN MAIN relay.

    3.

  3. This step tests for an open in the ground circuit to the IGN MAIN relay.

    4.

  4. This step tests if voltage is constantly being applied to the IGN MAIN relay.

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. With a scan tool, command the Ignition Power Relay (IGN MAIN Relay) ON and OFF.

Does the IGN MAIN relay turn ON and OFF with each command?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the IGN MAIN relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the control circuit of the IGN MAIN relay with a test lamp connected to a good ground.
  5. With a scan tool, command the IGN MAIN relay ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 4

Go to Step 5

4

  1. Connect a test lamp between the control circuit of the IGN MAIN relay and the ground circuit of the IGN MAIN relay.
  2. With a scan tool, command the IGN MAIN relay ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 9

Go to Step 8

5

Does the test lamp remain illuminated with each command?

Go to Step 6

Go to Step 7

6

Test the control circuit of the IGN MAIN relay for a short to B+. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 10

7
  1. Turn OFF the Ignition.
  2. Remove the harness connector from the body control module (BCM) that contains the IGN MAIN relay control circuit.
  3. Test the control circuit of the IGN MAIN relay for an open between the relay socket and the BCM harness connector.

    4. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 10

8
  1. Turn the ignition OFF.
  2. Test the ground of the IGN MAIN relay control circuit for an open between the relay socket and a good ground.

    3. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 9

9

Inspect for poor connections at the IGN MAIN relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 11

10

Inspect for poor connections at the console electrical center connector to the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 12

11

Replace the IGN MAIN relay.

Did you complete the replacement?

Go to Step 13

--

12

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

Did you complete the replacement?

Go to Step 13

--

13
  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