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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

Without BTM

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.

With BTM

The ignition mode switch has 2 LED's that indicate the vehicle power mode. When the vehicle is in the off mode, both LED's will be off. Pressing the ignition mode switch button once (without the brake pedal applied), the vehicle enters the accessory mode and the amber LED (ACC) will illuminate. The accessory mode has a 5 minute timeout to reduce battery drain. Pressing the ignition mode switch button a second time (without the brake pedal applied), the vehicle enters the run/start mode (without the engine running) and the green LED (Run/Start) will illuminate. Pressing and holding the push button start switch for at least 5 seconds will place the vehicle in run/start mode (without the vehicle running) and the green LED (Run/Start) will illuminate. With the ignition off (with the brake pedal applied), pressing the ignition mode switch button once, the vehicle will enter run/start mode and the green LED (run/start) will illuminate. This will start the engine. Both LED's have the voltage supplied from the BCM. The ignition mode switch sends the ignition mode switch status to the keyless entry control module and to the BCM. The keyless entry control module sends a redundant signal to the BCM with the ignition mode switch status.

The ignition mode switch contains two individual switches that provides redundant switch inputs to both the BCM and the keyless entry control module. The BCM supplies the ignition mode switch a constant B+ signal. The BCM monitors this signal to determine if the switch is released or pressed. When the ignition mode switch is not pressed, voltage on the signal circuit is pulled down through two resistors in the switch. When the ignition mode switch is pressed, voltage on the signal circuit is pulled down through only one resistor, changing the voltage seen at the BCM and indicating that the ignition mode switch is pressed.

The keyless entry control module monitors voltage on the switch is the same manner as the BCM, but monitors the second switch located in the ignition mode switch.

Reference Information

Schematic Reference

Power Distribution Schematics Power Distribution Schematics

Connector End View Reference

Component Connector End Views Outside Rearview Mirror - Driver

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

Without BTM

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. To isolate a short to ground, it may be necessary to also disconnect any control modules that are connected to the following circuits:

* S39 Ignition Switch - 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

• 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:

* K9 Body Control Module - Ignition circuit terminal 5

* K9 Body Control Module - Ignition circuit terminal 6

* K9 Body Control Module - Ignition circuit terminal 15

• 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. Disconnect the harness connector at the S39 Ignition Switch.

9. Test for less than 1 V between each of the ignition circuits listed below and ground:

* S39 Ignition Switch - Ignition circuit terminal 1

* S39 Ignition Switch - Ignition circuit terminal 3

* S39 Ignition Switch - Ignition circuit terminal 4

• If 1 V or greater, repair the short to voltage on the circuit

• If less than 1 V

10. Test or replace the S39 Ignition Switch.

With BTM

1. Ignition OFF and all systems OFF, disconnect the harness connector at the S38 Ignition Mode Switch. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 ohms between the ground circuit terminal 4 and ground.

• If 10 ohms or greater

1. Ignition OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

3. Test for less than 10 ohms between the low reference circuit terminal 7 and ground.

• If 10 ohms or greater

1. Ignition OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

4. Connect the S38 Ignition Mode Switch, ignition ON.

5. Verify the scan tool Body Control Module Push Button Ignition Switch Voltage parameter is greater than 11 V.

• If 11 V or less

1. Ignition OFF, disconnect the harness connector at the K9 Body Control Module.

2. Test for infinite resistance between the signal circuit terminal 6 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 greater than 11 V

6. Install a 3 A fused jumper wire between the signal circuit terminal 6 and ground.

7. Verify the scan tool Body Control Module Push Button Ignition Switch Voltage parameter is less than 1 V.

• If 1 V or greater

1. Ignition OFF, disconnect the harness connector at the K9 Body Control Module, ignition ON.

2. Test for less than 1 V between the signal circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.

• If less than 1 V

3. Test for less than 2 ohms in signal 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 less than 1 V

8. Connect the harness connector at the S38 Ignition Mode Switch.

9. Verify the scan tool Body Control Module Push Button Ignition Switch Voltage parameter is 8-10 V, with the S38 Ignition Mode Switch released.

• If not between 8-10 V
Test or replace the S38 Ignition Mode Switch.

• If between 8-10 V

10. Verify the scan tool Body Control Module Push Button Ignition Switch Voltage parameter is 4-7 V, with the S38 Ignition Mode Switch pressed.

• If not between 4-7 V
Test or replace the S38 Ignition Mode Switch.

• If between 4-7 V

11. Disconnect the X1 harness connector at the K84 Keyless Entry Control Module.

12. Test for infinite resistance between the signal circuit terminal 11 and ground.

• If less than infinite resistance
Repair the short to ground on the circuit.

• If infinite resistance

13. Ignition ON.

14. Test for less than 1 V between the signal circuit terminal 11 and ground.

• If 1 V or greater
Repair the short to voltage on the circuit.

• If less than 1 V

15. Test for 4.5-5.5k ohms between the signal circuit terminal 11 and the low reference circuit terminal 12, with the S38 Ignition Mode Switch released.

• If not between 4.5-5.5k ohms

1. Ignition OFF.

2. Test the signal circuit for an open/high resistance.

• If open/high resistance, repair the open/high resistance in the circuit.

• If not an open/high resistance, test or replace the S38 Ignition Mode Switch.

• If between 4.5-5.5k ohms

16. Test for 1-1.5k ohms between the signal circuit terminal 11 and the low reference circuit terminal 12, with the S38 Ignition Mode Switch pressed.

• If not between 1-1.5k ohms
Test or replace the S38 Ignition Mode Switch.

• If between 1-1.5k ohms

17. Test of replace the K84 keyless entry control module.

Component Testing

S39 Ignition Switch

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.





S38 Ignition Mode Switch

1. Ignition OFF, disconnect the harness connector at the S38 Ignition Mode Switch.

2. With the S38 Ignition Mode Switch released, test for 4.5-5.5k ohms between the terminals listed below:

* Signal terminal 6 and ground terminal 4

* Signal terminal 3 and low reference terminal 7

• If not between 4.5-5.5k ohms
Replace the S38 Ignition Mode Switch

• If between 4.5-5.5k ohms

3. With the S38 Ignition Mode Switch pressed, test for 1-1.5k ohms between the terminals listed below:

* Signal terminal 6 and ground terminal 4

* Signal terminal 3 and low reference terminal 7

• If not between 1-1.5k ohms
Replace the S38 Ignition Mode Switch.

• If between 1-1.5k ohms

4. 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 Body Control Module replacement, programming and setup

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