Diagnosis and Testing: Headlamps
Always begin any diagnosis by testing all of the fuses and circuit breakers in the system. For complete circuit diagrams, refer to SYSTEM WIRING DIAGRAMS .
HEADLAMP DIAGNOSIS
| CONDITION | POSSIBLE CAUSES | CORRECTION |
|---|---|---|
| HEADLAMPS ARE DIM WITH ENGINE IDLING OR IGNITION TURNED OFF. | 1. Loose or corroded battery cables. | 1. Clean and secure battery cable clamps and posts. |
| 2. Loose or worn generator drive belt. | 2. Adjust or replace generator drive belt. | |
| 3. Charging system output too low. | 3. Test and repair charging system. Refer to CHARGING - SERVICE INFORMATION . | |
| 4. Battery has insufficient charge. | 4. Test battery state - of - charge. Refer to BATTERY . | |
| 5. Battery is sulfated or shorted. | 5. Load test battery. Refer to BATTERY . | |
| 6. Poor lighting circuit Z1 - ground. | 6. Test for voltage drop across Z1 - ground locations. For complete circuit diagrams, refer to SYSTEM WIRING DIAGRAMS . | |
| 7. Both headlamp bulbs defective. | 7. Replace both headlamp bulbs. | |
| HEADLAMP BULBS BURN OUT FREQUENTLY. | 1. Charging system output too high. | 1. Test and repair charging system. Refer to CHARGING - SERVICE INFORMATION . |
| 2. Loose or corroded terminals or splices in circuit. | 2. Inspect and repair all connectors and splices. For complete circuit diagrams, refer to SYSTEM WIRING DIAGRAMS . | |
| HEADLAMPS ARE DIM WITH ENGINE RUNNING EVEN ABOVE IDLE.* | 1. Charging system output too low. | 1. Test and repair charging system. Refer to CHARGING - SERVICE INFORMATION . |
| 2. Poor lighting circuit Z1 - ground. | 2. Test for voltage drop across Z1 - ground locations. For complete circuit diagrams, refer to SYSTEM WIRING DIAGRAMS . | |
| 3. High resistance in headlamp circuit. | 3. Test amperage draw of headlamp circuit. | |
| 4. Both headlamp bulbs defective. | 4. Replace both headlamp bulbs. | |
| HEADLAMPS FLASH RANDOMLY. | 1. Poor lighting circuit Z1 - ground. | 1. Test for voltage drop across Z1 - ground locations. For complete circuit diagrams, refer to SYSTEM WIRING DIAGRAMS . |
| 2. High resistance in headlamp circuit. | 2. Test amperage draw of headlamp circuit. Should not exceed 30 amps. | |
| 3. Damaged or inoperative headlamps switch circuit breaker. | 3. Replace headlamp switch. | |
| 4. Loose or corroded terminals or splices in circuit. | 4. Inspect and repair all connectors and splices. For complete circuit diagrams, refer to SYSTEM WIRING DIAGRAMS . | |
| HEADLAMPS DO NOT ILLUMINATE. | 1. No voltage to headlamps. | 1. Repair open headlamp circuit. For complete circuit diagrams, refer to SYSTEM WIRING DIAGRAMS . |
| 2. No Z1 - ground at headlamps. | 2. Repair circuit ground. For complete circuit diagrams, refer to SYSTEM WIRING DIAGRAMS . | |
| 3. Damaged or inoperative headlamp switch. | 3. Replace headlamp switch. | |
| 4. Damaged or inoperative headlamp dimmer (multi-function) switch. | 4. Replace multi-function switch. | |
| 5. Broken connector terminal or wire splice in headlamp circuit. | 5. Repair connector terminal or wire splice. | |
| (DRL EQUIPPED VEHICLES) HEADLAMPS STAY ON WITH KEY REMOVED. | 1. Inoperative DRL. | 1. Using a scan tool, check CCN and TIPM for DTC's, and then check inputs/outputs. Refer to appropriate Diagnostic Information. DRL functionality is covered by the TIPM headlamps will stay ON with key in RUN and if TIPM is getting left multi-function switch status message as SNA from SCCM which has headlamp switch integrated into it. |
| *Canada vehicles must have lamps ON. | ||