Vehicle Will Not Change Power Mode
Vehicle Will Not Change Power Mode
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information
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
Power Distribution Schematics Power Distribution Schematics
Connector End View Reference
Component Connector End Views Sunshade - Left Front
Description and Operation
Power Mode Description and Operation Power Mode
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Ignition ON.
2. Verify the scan tool power mode parameters change when cycling the S39 ignition switch between OFF, Accessory, ON, and Start.
• If the parameters do not change
Refer to Circuit/System Testing.
• If the parameters change
3. All OK.
Circuit/System Testing
1. Ignition ON, disconnect the harness connector at the S39 ignition switch while the ignition is ON.
2. Verify a test lamp illuminates between the B+ circuit terminal 2 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. Test for less than 2 ohms in the B+ circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the B+ circuit and ground.
• If less than infinite resistance, repair the short to ground on one of the following circuits listed below:
• If infinite resistance
Note:
To help isolate a short to ground, it may be necessary to disconnect modules that are connected to the following circuits:
* B+ circuit terminal 2 - S39 ignition switch
* Ignition circuit terminal 1 - S39 ignition switch
* Ignition circuit terminal 3 - S39 ignition switch
* Ignition circuit terminal 4 - S39 ignition switch
* Ignition circuit terminal 6 - S39 ignition switch
• If the test lamp illuminates
3. Ignition ON.
4. Test for 4.8-5.2 V between the 5 V reference circuit terminal 6 and ground.
• If less than 4.8 V
1. Ignition OFF, disconnect the X3 harness connector at the K9 body control module.
2. Test for infinite resistance between the 5 V reference circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
3. Test for less than 2 ohms in the 5 V reference circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K9 body control module.
• If greater than 5.2 V
1. Ignition OFF, disconnect the X3 harness connector at the K9 body control module.
2. Test for less than 1 V between the 5 V reference circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K9 body control module.
• If between 4.8-5.2 V
5. Connect the harness connector at the S39 ignition switch.
6. Ignition OFF, disconnect the X3 harness connector at the K9 body control module, ignition ON.
7. Verify a test lamp illuminates between each of the ignition circuits listed below and ground:
* Ignition circuit terminal 5 - K9 body control module
* Ignition circuit terminal 6 - K9 body control module
* Ignition circuit terminal 15 - K9 body control module
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. Test for less than 2 ohms in the ignition circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the ignition circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the K9 body control module.
• If the test lamp illuminates
8. Test or replace the S39 ignition switch.
Component Testing
1. Ignition OFF, disconnect the X1 harness connector at the S39 ignition switch.
2. Using the Resistance Test below, verify the resistance between the terminals listed below match for each S39 ignition switch position.
• If any reading is other than specified
Replace the S39 ignition switch.
• If the readings match
3. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Ignition and Start Switch Replacement Ignition and Start Switch Replacement
* Control Module References Control Module References for BCM replacement, programming and setup