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Tahoe / Yukon Service Manual

DTC B1578 - Liftgate Close Switch Malfunction

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 DTC Descriptor DTC B1578 Rear Closure Shut Face Switch Signal Symptom Byte Information: Symptom Byte List Diagnostic Fault Information

Circuit number Circuit Function Short to Ground Open/High Resistance Short to Voltage Signal Performan
4657 Signal B1578 00 1 — —
4656 Low Reference — 1 — —
1. B70 Liftgate Close Switch = Inoperative

Circuit/System Description The K194 Rear Gate Module provides the B70 Liftgate Close Switch with approximately 12V to the signal circuit 4657. Ground is provided by the K194 Rear Gate Module through low reference circuit 4656. When the switch is pressed, the K194 Rear Gate Module will detect the voltage drop in the signal circuit 4657 and will command the power liftgate to perform the CLOSE function. Conditions for Running the DTC Ignition » On / Vehicle » In Service Mode Conditions for Setting the DTC 4657=Short to Ground For greater than 60 s Actions Taken When the DTC Sets B70 Liftgate Close Switch = Disabled Conditions for Clearing the DTC A current DTC will clear when the diagnostic runs and passes. A history DTC will clear after 40 consecutive malfunction-free ignition cycles. Reference Information Schematic Reference Schematic Reference Liftgate Schematics Connector End View Reference Master Electrical Component List Description and Operation Liftgate 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. Ignition » On / Vehicle » In Service Mode
  2. Verify the scan tool parameter: Rear Gate Close Switch = Inactive ⇒ If not the specified state Refer to: Circuit/System Testing ⇓ If the specified state
  3. Operate the component: B70 Liftgate Close Switch » Pressed Verify the scan tool parameter: Rear Gate Close Switch = Active ⇒ If not the specified state Refer to: Circuit/System Testing ⇓ If the specified state
  4. A fault is not currently present and may be an intermittent condition Circuit/System Testing
  5. Ignition/Vehicle & All vehicle systems » Off
  6. Disconnect the electrical connector: B70 Liftgate Close Switch
  7. Verify a test lamp turns On between the test points: Low Reference terminal 1 & B+ ⇒ If the test lamp does not turn On 3.1. Test circuit 4656 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. 3.2. Replace the K194 Rear Gate Module. ⇓ If the test lamp turns On
  8. Ignition » On / Vehicle » In Service Mode
  9. Verify the scan tool Rear Gate Close Switch parameter is Inactive ⇒ If not Inactive 5.1. Test the circuit 4657 for a short to ground ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found. 5.2. Replace the K194 Rear Gate Module. ⇓ If Inactive
  10. Install a 3 A fused jumper wire between the signal circuit terminal 3 and ground.
  11. Verify the scan tool parameter is now Active. ⇒ If not Active and the 3 A fuse is OK 7.1. Test the circuit 4657 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. 7.2. Replace the K194 Rear Gate Module. ⇒ If not Active and the 3 A fuse is open 7.1. Test the circuit 4657 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found. 7.2. Replace the K194 Rear Gate Module. ⇓ If Active
  12. Test or replace the component: B70 Liftgate Close Switch Component Testing
  13. Ignition/Vehicle » Off
  14. Disconnect the electrical connector: B70 Liftgate Close Switch
  15. Test for infinite resistance between the test points: Signal terminal 3 & Low Reference terminal 1 — Switch » Not Pressed ⇒ If less than infinite resistance Replace the component: B70 Liftgate Close Switch ⇓ If infinite resistance
  16. Test for less than 3 Ω between the test points: Signal terminal 3 & Low Reference terminal 1 — Switch » Pressed ⇒ If 3 Ω or greater Replace the component: B70 Liftgate Close Switch ⇓ If less than 3 Ω
  17. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Liftgate Close Switch Replacement For control module replacement, programming, and setup refer to: Control Module References