GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC B1370: Device Ignition 1 Circuit

DTC B1380: Device Ignition ACCESSORY Circuit

DTC B1385: Device Ignition START Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

B+ Terminal A, X1 with LS4 or Terminal 4 without LS4

B1370, B1380, B1385

B1370, B1380, B1385

B1370, B1380, B1385

B+ Terminal A, X2 with LS4 or Terminal 6 without LS4

B1370, B1380, B1385

B1370, B1380, B1385

B1370, B1380, B1385

Ignition Terminal C, X2 with LS4 or Terminal 3 without LS4

B1380

B1380

B1380

Ignition Terminal B, X2 with LS4 or Terminal 7 without LS4

B1370

B1370

B1370

Ignition Terminal B, X1 with LS4 or Terminal 5 without LS4

B1385

B1385

B1385

Circuit/System Description

The vehicle power mode master (PMM) is the body control module (BCM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination of the power mode. The PMM receives the ignition switch signals, and additionally a reference voltage signal from the BCM, through the ignition switch, and back to the BCM. There are redundancies within the PMM system that can allow operation of certain subsystems when there are faults in the ignition switch circuits. Other information such as serial data input from other modules and DTCs is also used to determine what power mode signals and information is transmitted by the PMM. The BCM logic uses all this information to identify the operator's desired power mode and activate specific discrete signals, and serial data messages for the operation of different subsystems as necessary. Other modules which have switched voltage inputs may operate in a default mode if the PMM serial data message does not match what the individual module can detect from its own connections.

The PMM will activate relays and other direct outputs of the PMM as needed according to the calculated power mode. Some relays controlled by the BCM are switched ignition voltage outputs that are pass through circuits within the BCM directly from the ignition switch. If these circuits short to ground, the B+ circuit fuse to the ignition switch will open.

Conditions for Running the DTC

    • The BCM must be powered and must detect a change in the ignition switch circuit states.
    • The vehicles battery must be fully charged.

Conditions for Setting the DTC

B1370

The BCM detects that the ignition 1 signal is shorted to ground, voltage, or open.

B1380

The BCM detects that the ignition 3 signal is shorted to ground, voltage, or open.

B1385

The BCM detects that the crank signal is shorted to ground, voltage or open.

Actions Taken When the DTC Sets

    • The BCM stores DTC to memory.
    • The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the serial data communications circuits.
    • The other modules on the vehicle operate in a fail-safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the serial data communications circuits.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

Diagnostic Aids

    • A short to ground in the ignition circuit of the run crank relay will cause an open fuse to the ignition switch. DTC B1428 should be current.
    • The power modes and controls are determined using BCM logic. Comparing the Body Control Module Power Mode data display parameters listed in Circuit/System Verification to the scan tool values of the vehicle will determine if there is a power mode fault.

Reference Information

Schematic Reference

    •  Power Distribution Schematics
    •  Power Moding Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Power Mode Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

With a scan tool, access BCM, Power Mode data display list and compare all parameters listed with the corresponding ignition key position. The PMM Power Mode Parameters table below illustrates the correct state of these input parameters in correspondence to the ignition switch position.

If any parameters are incorrect in any key position, refer to the Circuit/System Testing or Component Testing.

PMM Power Mode Parameters

Ignition Switch Position

Starter Switch

Accessory Switch

Ignition Run Start Switch

Operating Conditions: Drivers door open to disable RAP

Off

Released

Inactive

Inactive

Accessory

Released

Active

Inactive

Run

Released

Active

Active

Start

Cranking

Inactive

Active

Circuit/System Testing

    Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

  1. Connect a test lamp between each fuse test terminal of the ignition switch B+ circuit fuse and ground. The test lamp should illuminate.
  2. If the test lamp does not illuminate, test the ignition switch circuits listed below for a short to ground. If all circuits test OK, replace the BCM.
    • B+ terminal A, X1 - with LS4
    • B+ terminal 4 - without LS4
    • B+ terminal A, X2 - with LS4
    • B+ terminal 6 - without LS4
    • Ignition terminal B, X1- with LS4
    • Ignition terminal 5 - without LS4
    • Ignition terminal B, X2 - with LS4
    • Ignition terminal 7 - without LS4
    • Ignition terminal C, X2 - with LS4
    • Ignition terminal 3 - without LS4
  3. Disconnect the harness connector at the ignition switch.
  4. Connect a test lamp between the ignition switch terminals listed below and ground. The test lamp should illuminate.
  5. If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
    • B+ terminal A, X1 - with LS4
    • B+ terminal A, X2 - with LS4
    • B+ terminal 4 - without LS4
    • B+ terminal 6 - without LS4

    Important: The ignition switch component test must be performed before proceeding with this test to verify the integrity of the switch.

  6. Perform the ignition switch component test. Verify the switch passes the test.
  7. If the ignition switch does not test normal, replace the ignition switch.
  8. Disconnect the X1 harness connector at the BCM, test for less than 1.0 volt between the circuit terminals of the BCM listed below and ground:
  9. • 12-volt reference terminal 25
    • Ignition terminal 21
    • Ignition terminal 22
    • Ignition terminal 23
    If greater than specified, test the circuit for a short to voltage.
  10. Test for less than 1.0 ohm between the BCM and the ignition switch on the circuits listed below:
  11. • 12-volt reference terminal 25, X1 and A, X1 - with LS4
    • 12-volt reference terminal 25, X1 and 4 - without LS4
    • 12-volt reference terminal 25, X1 and A, X2 - with LS4
    • 12-volt reference terminal 25, X1 and 4 - without LS4
    • Ignition terminal 21, X1 and B, X1 - with LS4
    • Ignition terminal 21, X1 and 5 - without LS4
    • Ignition terminal 22, X1 and B, X2 - with LS4
    • Ignition terminal 22, X1 and 7 - without LS4
    • Ignition terminal 23, X1 and C, X2 - with LS4
    • Ignition terminal 23, X1 and 3 - without LS4
    If greater than specified, test the circuit for open/high resistance.
  12. If all circuits test normal, replace the BCM.

Component Testing

Ignition Switch

Using the Resistance Test below, check the resistance between the terminals of the ignition switch listed in each switch position listed.

If any reading is other than specified, replace the ignition switch.

Resistance Test

Ignition Switch Position

Terminals (A, X2 and B, X1 with LS4) or (5 and 6 without LS4)

Terminals (A, X1 and AX2 with LS4) or (4 and 6 without LS4)

Terminals A, X1 and C, X2 with LS4) or (3 and 4 without LS4)

Terminals (A, X1 and B, X2 with LS4) or (4 and 7 without LS4)

Off

Infinite

Infinite

Infinite

Infinite

Accessory

Infinite

Infinite

< 5.0 ohms

Infinite

Run

Infinite

Infinite

< 5.0 ohms

< 5.0 ohms

Start

< 5.0 ohms

Infinite

Infinite

< 5.0 ohms

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  Control Module References for module replacement, setup, and programming
    •  Ignition and Start Switch Replacement