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Tahoe / Yukon Service Manual

Ignition Mode Switch Indicator Malfunction

Wiring Systems and Power Management | Diagnostic Information and Procedures | Document ID: 5493994 Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions Diagnostic Fault Information

Circuit Number Circuit Function Short to Ground Open/High Resistance Short to Voltage Signal Performanc
5720 Control 1 1 B1A2 12 2 —
5719 Control 3 3 B1AC3 12 4 —
1851 Ground — 1, 3 — —
1. Accessory power indicator is always OFF. 2. Accessory power indicator is always ON. 3 Ignition Run Mode Indicator Always OFF. 4. Ignition Run Mode Indicator Always ON

Circuit/System Description The S38 On/Off Vehicle Switch contains two individual switches that provide redundant switch inputs to both the K9 Body Control Module (BCM) (Power Mode Master)and the K56 Serial Data Gateway Module (Back Up Power Mode Master). The K9 Body Control Module supplies the S38 On/Off Vehicle Switch a constant 5 v signal on Signal Circuit  5723. The K9 Body Control Module monitors this signal to determine if the switch is released or pressed. When the S38 On/Off Vehicle Switch is not pressed, voltage on the signal circuit 5723 is pulled down through two resistors in the switch by ground circuit 1851. When the S38 On/Off Vehicle Switch is pressed, voltage on the signal circuit 5723 is pulled down through only one resistor by ground circuit 1851, the voltage change seen by the K9 Body Control Module indicates that the S38 On/Off Vehicle Switch is pressed. If a fault is detected on signal circuit 5723 or ground circuit 1851 a DTC will set. The K56 Serial Data Gateway Module supplies the S38 On/Off Vehicle Switch with a 5 v on signal circuit 3558 while the module is awake & low reference circuit 3559. The K56 Serial Data Gateway Module monitors this signal to determine if the switch is released or pressed. When the S38 On/Off Vehicle Switch is not pressed, voltage on the signal circuit 3558 is pulled down through two resistors in the switch by low reference circuit  3559. When the S38 On/Off Vehicle Switch is pressed, voltage on the signal circuit 3558 is pulled down through only one resistor in the switch by low reference circuit 3559, the changing the voltage seen at the K56 Serial Data Gateway Module indicates that the S38 On/Off Vehicle Switch is pressed. The K56 Serial Data Gateway Module is the vehicles backup power mode master. If a fault is detected on signal circuit 3558 or low reference circuit 3559 a DTC will set. The S38 On/Off Vehicle Switch has two LEDs that indicate the vehicle power mode. When the vehicle is in the off mode, both LEDs will be off. Pressing the S38 On/Off Vehicle Switch button momentarily without the brake pedal applied, the vehicle will enter the accessory mode, the K9 Body Control Module supplies a pulse width modulated voltage on control circuit 5720 to illuminate the amber LED (accessory), the LED is grounded through the switch by ground circuit 1851. The accessory mode has a time-out up to 5 min to help reduce battery drain. Pressing and holding the push button start switch without the brake pedal applied for 5  s will place the vehicle in Run Mode (Ignition On without the Propulaion Active), the K9 Body Control Module supplies a pulse width modulated voltage on control circuit 5719 to illuminate the green LED (Run/Start/Propulsion), the LED is grounded through the switch by ground circuit 1851. With the ignition off brake pedal applied, pressing the S38 On/Off Vehicle Switch button once, the vehicle will enter Vehicle Start/Propulsion Mode this will start the Propulaion system, the K9 Body Control Module supplies a pulse width modulated voltage on control circuit 5719 to illuminate the green LED (Run/Start), the LED is grounded through the switch by ground circuit 1851. If the vehicle is in Propulsion Mode and vehicle speed above 4 km/h (2.5 mph) is detected and the S38  On/Off Vehicle Switch is pressed for greater than 2 s or is pressed 2 times within 5 s the vehicle will enter the Run Mode (Ignition On without the Propulaion Active). Reference Information Schematic Reference Power Moding Schematics Power Distribution Schematics Connector End View Reference Master Electrical Component List 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. Cycle the ignition between Run Mode and OFF.
  2. Verify the green Run Mode indicator turns on and off. ⇒ The Run Mode indicator does not turn on and off
  3. Verify the scan tool Power Mode value Is Run ⇒ If the value is not Run Refer to: Vehicle Will Not Change Power Mode ⇓ If the value is Run
  4. Refer to Circuit/System — Test — Run/Crank Mode Indicator Malfunction. ⇓ The Run Mode indicator turns on and off
  5. Cycle the ignition between Accessory Mode and OFF.
  6. Verify the Yellow Accessory indicator turns on and off. ⇒ If the indicator does not turn on and off
  7. Verify the scan tool Power Mode value Is Accessory ⇒ If the value is not Accessory Refer to: Vehicle Will Not Change Power Mode ⇓ If the value is Accessory
  8. Refer to Circuit/System — Test — Accessory Mode Indicator Malfunction. ⇓ If the Specified State
  9. A fault is not currently present and may be an intermittent condition. Circuit/System Testing Test — Run/Crank Mode Indicator Malfunction
  10. Ignition OFF, disconnect the connector at the S38 On/Off Vehicle Switch.
  11. Verify a test lamp illuminates between ground terminal 3 and B+ ⇒ If the test lamp does not illuminate Repair the open/high resistance on circuit 1851 or ground connection. ⇓ If the test lamp illuminates
  12. Connect the connector at the S38 Vehicle On/Off Switch.
  13. Connect a test lamp between control circuit terminal 1 and ground terminal 3 at the S38 Vehicle On/Off switch.
  14. Verify the test lamp turns On and Off while repeatedly cycling the ignition between Run and Off. ⇒ If the test lamp does not turn on and off 5.1. Test the control circuit 5719 for a short to ground. ⇒ If a short to ground is found repair the fault in the circuit ⇓ If a short to ground is not found 5.2. Test the control circuit 5719 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open or high resistance is not found 5.3. Ignition ON, disconnect connector at the S38 Vehicle On/Off Switch and connector X3 at the K9 Body Control Module. 5.4. Test less than 1 V Between control circuit 5719 and ground. ⇒ If 1 V or greater Repair the short to voltage on circuit 5719. ⇓ If less than 1 V 5.5. Replace the K9 Body Control Module. ⇓ If the Test lamp turns on and off
  15. Replace the S38 Vehicle On/Off Switch. Test — Accessory Mode Indicator Malfunction
  16. Ignition OFF, disconnect the connector at the S38 On/Off Vehicle Switch.
  17. Verify a test lamp illuminates between the ground circuit terminal 3 and B+ ⇒ If the test lamp does not illuminate Repair the open/high resistance on circuit 1851 or ground connection. ⇓ If the test lamp illuminates
  18. Connect the connector at the S38 Vehicle On/Off Switch.
  19. Connect a test lamp between control circuit terminal 2 and ground terminal 3 at the S38 Vehicle On/Off switch.
  20. Verify the test lamp turns On and Off while repeatedly cycling the ignition between Accessory and Off. ⇒ If the test lamp does not turn on and off 5.1. Test the control circuit 5720 for a short to ground. ⇒ If a short to ground is found repair the fault in the circuit ⇓ If a short to ground is not found 5.2. Test the control circuit 5720 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 5.3. Ignition ON, disconnect connector at the S38 Vehicle On/Off Switch and connector X2 at the K9 Body Control Module. 5.4. Test less than 1 V Between control circuit 5720 and ground. ⇒ If 1 V or greater Repair the short to voltage on circuit 5720. ⇓ If less than 1 V 5.5. Replace the K9 Body Control Module. ⇓ If the Test lamp turns on and off
  21. Replace the S38 Vehicle On/Off Switch. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification On/Off Vehicle Switch Replacement For control module replacement, programming, and setup refer to: Control Module References