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Tahoe / Yukon Service Manual

Automatic Day-Night Mirrors Malfunction

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 Number Circuit Function Short to Ground Open/High Resistance Short to Voltage Signal Performance
1839 Ignition 1 1 — —
1690 Signal 2 2 2 —
24 Control B1236 11 1 1 —
1691 Low Reference — 2 2 —
2351 Ground — 1 — —
1. Inside and Outside Rearview Mirror Automatic Dimming Malfunction 2. Outside Rearview Mirror Automatic Dimming Malfunction

Circuit/System Description The inside rearview mirror uses 2 photocell sensors. One sensor is the rear light sensor, located on the face side of the mirror, facing the rear of the vehicle. The rear light sensor is used to determine light conditions present at the mirror face. The other sensor is the front light sensor, located on the backside of the mirror, facing the front of the vehicle. The front light sensor is used to determine the exterior light conditions at the front of the vehicle. With a low exterior light condition detected by the front light sensor and a high light condition from the rear light sensor, the inside rearview mirror will automatically darken the face of the inside rearview mirror and the driver outside rearview mirror. The inside rearview mirror provides a control circuit and a low reference circuit to the driver outside rearview mirror to darken the mirror when needed. With the gear selector lever in the REVERSE position and the engine running, backup lamp control voltage is supplied as an input to the inside rearview mirror. The mirror monitors this input to disable the automatic day-night feature. This allows the driver to see objects in the mirrors clearly when backing up, regardless of the rear light sensor status. Diagnostic Aids Before replacing anything verify the following: Both backup lamps (left & right) are working properly. Refer to Backup Lamps Malfunction The customer has not installed LED bulbs in the place of incandescent bulbs. Reference Information Inside Rearview Mirror Schematics Outside Rearview Mirror Schematics Connector End View Reference Master Electrical Component List Description and Operation Automatic Day-Night Mirror 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.
  2. Cover the windshield with a blanket or other suitable item.
  3. Verify the A10 Inside Rearview Mirror face dims when shining a bright light into the rear light sensor ⇒ If the A10 Inside Rearview Mirror does not dim Refer to Circuit/System Testing — Inside Review Mirror Dimming Inoperative ⇓ If the A10 Inside Rearview Mirror dims
  4. Verify the A10 Inside Rearview Mirror face transitions from dim to bright while commanding the Backup Lamps Active and Inactive with a scan tool. ⇒ If the A10 Inside Rearview Mirror does not transition between dim and bright. Refer to Circuit/System Testing — Day-Night Disable Malfunction ⇓ If the A10 Inside Rearview Mirror transitions between bright and dim states
  5. Verify the A9A Outside Rearview Mirror-Driver face dims when shining a bright light into the rear light sensor. ⇒ If the A9A Outside Rearview Mirror-Driver does not dim Refer to Outside Rearview Mirror Dimming Malfunction. ⇓ If the A9A Outside Rearview Mirror-Driver dims
  6. Verify the A9A Outside Rearview Mirror-Driver face transitions from dim to bright while commanding the Backup Lamps Active and Inactive with a scan tool. ⇒ If the A9A Outside Rearview Mirror-Driver does not transition between bright and dim states Refer to Outside Rearview Mirror Dimming Malfunction. ⇓ If the A9A Outside Rearview Mirror-Driver transitions between bright and dim states
  7. A fault is not currently present and may be an intermittent condition. Circuit/System Testing Inside Review Mirror Dimming Inoperative
  8. Ignition OFF and all vehicle systems OFF, disconnect the connector at the A10 Inside Rearview Mirror. It may take up to 2 minutes for all vehicle systems to power down.
  9. Verify a test lamp illuminates between ground circuit terminal 5 and B+. ⇒ If the test lamp does not illuminate 2.1. Repair the open/high resistance on the ground circuit or ground connection. ⇓ If the test lamp illuminates
  10. Ignition ON.
  11. Verify a test lamp illuminates between the ignition circuit terminal 2 and ground. ⇒ If the test lamp does not illuminate 4.1. Test circuit 1839 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. 4.2. Test circuit 1839 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. 4.3. Replace X51A Fuse Block — Instrument Panel for an internal fault. ⇓ If the test lamp illuminates
  12. Replace the A10 Inside Rearview Mirror. Day-Night Disable Malfunction
  13. Ignition OFF, disconnect the connector at the A10 Inside Rearview Mirror.
  14. Connect a test lamp between the control circuit terminal 1 and ground
  15. Ignition ON, verify the test lamp turns ON and OFF while commanding the Backup Lamps Active and Inactive with a scan tool. ⇒ If the test lamp is always OFF 3.1. Test circuit 24 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. 3.2. Test circuit 24 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. Refer to Backup Lamps Malfunction ⇒ If the test lamp is always ON 3.1. Test circuit 24 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. Refer to Backup Lamps Malfunction ⇓ If the test lamp turns ON and OFF
  16. Replace the A10 Inside Rearview Mirror. Outside Rearview Mirror Dimming Malfunction
  17. Ignition OFF and all vehicle systems OFF, disconnect the X510 inline connector at the A9A Outside Rearview Mirror-Driver. It may take up to 2 minutes for all vehicle systems to power down.
  18. Verify a test lamp illuminates between the low reference circuit terminal 12 and ground. ⇒ If the test lamp does not illuminate 2.1. Test circuit 1691 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. 2.2. Replace A10 Inside Rearview Mirror for an internal fault. ⇓ If the test lamp illuminates
  19. Ignition ON.
  20. Test for less than 1 V between the control circuit terminal 17 and ground. ⇒ If 1 V or greater 4.1. Test circuit 1690 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. 4.2. Replace the A10 Inside Rearview Mirror. ⇓ If less than 1 V
  21. Ignition ON, headlamps ON, vehicle in PARK, cover the front light sensor with a towel or other suitable item. Shine a flashlight at the rear light sensor.
  22. Test for greater than 1 V between the control circuit terminal 2 and ground. ⇒ If 1 V or less 6.1. Test circuit 1690 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. 6.2. Test circuit 1690 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. 6.3. Replace A10 Inside Rearview Mirror for an internal fault. ⇓ If greater than 1 V
  23. Replace E17D Outside Rearview Mirror Glass-Driver. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Inside Rearview Mirror Replacement Outside Rearview Mirror Glass Replacement