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Power Mode Mismatch

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.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

B+ - Terminal 2

B1370 04, B1380 04

B1370 04, B1380 04

--

--

Ignition - Terminal 3

B1370 04, B1380 04

B1380 04

B1380 01

--

Ignition - Terminal 4

B1370 04, B1380 04, B1441 04

B1441 04

B1441 01

--

Ignition - Terminal 1

B1370 04, B1380 04

B1370 04, B1380 04

B1370 01

--

Ignition - Terminal 6

--

1

--

--

1. Power Mode Mismatch

Circuit/System Description

The vehicle power mode master is the body control module (BCM). The ignition switch is a low current switch with multiple discrete circuits to the BCM. The BCM logic uses the ignition switch positions 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 power mode master serial data message does not match what the individual module can detect from its own connections.

The power mode master will activate relays and other direct outputs of the power mode master 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.

Reference Information

Schematic Reference

    •  Body Control System Schematics
    •  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

  1. Verify that DTC U1814 is not set.
  2. If DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  3. With a scan tool, access Power Mode data display list and compare all parameters listed with the corresponding ignition key position. The Power Mode Parameters table below illustrates the correct state of these input parameters in correspondence to the S39 Ignition Switch. The circuits which the individual parameters are related to are in parentheses.
  4. If any parameters are incorrect in any key position, proceed to the Circuit/System Testing or Component Testing.

Power Mode Parameters

S39 Ignition Switch Position

Current Power Mode

Ignition Off/Run/Crank

(Switch, Terminal 4)

Ignition Accessory/Run

(Switch, Terminal 3)

Ignition Run/Crank

(Switch, Terminal 1)

Off Key Out

Off

Key Out/ACCY

Inactive

Inactive

Off Key IN

Off

Key In/Off

Inactive

Inactive

Accessory

Accessory

Key Out/ACCY

Active

Inactive

Run

Run

Run

Active

Active

Start

Crank Request

Crank

Inactive

Active

Circuit/System Testing

  1. Ignition OFF, disconnect the X1 harness connector at the S39 Ignition Switch.
  2. Verify that a test lamp illuminates between B+ circuit terminal 2 and ground.
  3. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the ignition circuits listed below for a short to ground.

    Note: To help isolate a short to ground, it may be necessary to disconnect modules that are connected to the following circuits:

       •  Terminal 1
       • Terminal 3
       • Terminal 4
       • Terminal 6

  4. Connect the harness connector at the S39 Ignition Switch.
  5. Ignition OFF, key out, disconnect the X3 harness connector at the K9 Body Control Module. Verify that a test lamp does not illuminate between the ignition circuit terminals listed below and ground:
  6. • Terminal 5
    • Terminal 6
    • Terminal 15
    • Terminal 22
    If the test lamp illuminates, test the ignition circuits for a short to voltage. If the circuit tests normal, replace the S39 Ignition Switch.
  7. Ignition in the ACCESSORY position, verify that a test lamp illuminates between the terminal 5 and ground.
  8. If the test lamp does not illuminate, test the ignition circuit for an open/high resistance. If the circuit tests normal, replace the S39 Ignition Switch.
  9. Ignition in the CRANK position, verify that a test lamp illuminates between terminal 1 and ground.
  10. If the test lamp does not illuminate, test the ignition circuit for an open/high resistance. If the circuit tests normal, replace the S39 Ignition Switch.
  11. If all of the circuits test normal, replace the K9 Body Control Module.

Component Testing

Ignition Switch

  1. Ignition OFF, disconnect the harness connector at the S39 Ignition Switch.
  2. Verify the resistance between the terminals listed below match for each S39 Ignition Switch.
  3. If not the specified value, replace the S39 Ignition Switch.

Resistance Test

S39 Ignition Switch Position

Terminals 1 and 2

Terminals 2 and 3

Terminals 2 and 4

Terminals 2 and 6

Terminals 4 and 6

Off Key Out

Infinite

Infinite

Infinite

Infinite

Infinite

Off Key IN

Infinite

Infinite

< 5.0 Ω

Infinite

Infinite

Accessory

Infinite

< 5.0 Ω

Infinite

Infinite

Infinite

Run

< 5.0 Ω

< 5.0 Ω

Infinite

Infinite

< 5.0 Ω

Start

< 5.0 Ω

Infinite

Infinite

Infinite

1275-1325 Ω

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

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


© Copyright Chevrolet. All rights reserved
   


© Copyright Chevrolet. All rights reserved