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1. Ignition OFF, disconnect the headlamp low/HID relay. 2. Ignition ON, verify that a test lamp does not illuminate between the headlamp control circuit terminal 87 and ground. If the test lamp illuminates, test the headlamp control circuit for a short to voltage. 3. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground. If the test lamp does not illuminate, replace the underhood fuse block. 4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground. If the test lamp does not illuminate, replace the underhood fuse block. 5. Disconnect the harness connector at the affected headlamp. 6. Test for less than 1 ohm of resistance between the headlamp ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance. 7. Connect the harness connector at the headlamp. 8. Connect a 20A fused jumper wire between the B+ circuit terminal 30 and the headlamp control circuit terminal 87. Verify the low beam headlamps are on. If the headlamps do not turn on, test the control circuit for an open/high resistance. If 9. Connect a test lamp between the B+ circuit terminal 85 and the relay control circuit terminal 86. 10. Command the Low Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the relay control circuit for a short to ground. If the If the test lamp is always OFF, test the relay control circuit for a short to voltage or an 11. If all circuits test normal, test or replace the headlamp low/HID relay. High Beam Relay Control Circuit Test 1. Ignition OFF, disconnect the harness connector X4 at the BCM. 2. Low beam headlamps ON, verify the high beam headlamps are not on. If the high beam headlamps are on, test the high beam relay control circuit for a short 3. Install a 10A fused jumper wire between the relay control circuit terminal 16 and ground. Verify the high beam headlamps are on.
2008 Chevrolet Silverado 1500 2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
If the high beam headlamps are not on, test the high beam relay control circuit for an 4. If all circuits test normal, replace the BCM. High Beam Headlamp Circuit Test 1. Ignition OFF, disconnect the harness connector at the affected headlamp. 2. Test for less than 1 ohm of resistance between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance. 3. Connect a test lamp between the control circuit terminal A and the ground circuit terminal B. 4. Command the High Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to voltage. If the If the test lamp is always OFF, test the control circuit for a short to ground or an 5. If all circuits test normal, test or replace the affected headlamp. Repair Procedures Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Headlamp Bulb Replacement (GMC) or Headlamp Bulb Replacement (Chevrolet) Headlamp Switch Replacement (without RPO SLT) or Headlamp Switch Turn Signal Multifunction Switch Replacement Control Module References for BCM replacement, programming, and setup. HEADLAMPS FLASH TO PASS INOPERATIVE 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. Circuit/System Description
2008 Chevrolet Silverado 1500 2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
The high beam headlamps are controlled by the BCM through the high beam relay. The relay is Reference Information Schematic Reference Headlights/Daytime Running Lights (DRL) Schematics Connector End View Reference Component Connector End Views Description and Operation Exterior Lighting Systems 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 With the headlamps ON, observe the scan tool Flash to Pass Switch parameter while pulling and Circuit/System Testing 1. Ignition OFF, disconnect the harness connector X2 at the turn signal/multifunction switch. 2. Test for less than 1 ohm of resistance between the ground circuit terminal D and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
2008 Chevrolet Silverado 1500 2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
3. Ignition ON, verify the scan tool Flash to Pass Switch parameter is Inactive. If not the specified value, test the signal circuit terminal A for a short to ground. If the 4. Install a 3A fused jumper wire between the signal circuit terminal A and the ground circuit terminal D. Verify the scan tool Flash to Pass Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high 5. If all circuits test normal, test or replace the signal/multifunction switch. Repair Procedures Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Turn Signal Multifunction Switch Replacement Control Module References for BCM replacement, programming, and setup. HIGH BEAM INDICATOR 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. Circuit/System Description The instrument panel cluster (IPC) illuminates the high beam indicator when the BCM detects Reference Information Schematic Reference Instrument Cluster Schematics Connector End View Reference Component Connector End Views Description and Operation
2008 Chevrolet Silverado 1500 2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
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