Diagnostic procedures
When a vehicle experiences problems with the
headlamp system, verify the condition of the battery
connections, fuses, charging system, headlamp bulbs,
wire connectors, relay, high beam switch, dimmer
switch, and headlamp switch. Refer to Group 8W,
Wiring Diagrams for component locations and circuit
information.
System diagnosis
HEADLAMP
Always begin any diagnosis by testing all of the
fuses and circuit breakers in the system. Refer to
Group 8W, Wiring Diagrams.
Conventional and halogen headlamps are interchangeable.
It is recommended that they not be
intermixed on a given vehicle.
CONDITION |
POSSIBLE CAUSES |
CORRECTION |
HEADLAMPS ARE DIM
WITH ENGINE IDLING
OR IGNITION TURNED
OFF |
- Loose or corroded battery cables.
- Loose or worn generator drive
belt.
- Charging system output too low.
- Battery has insufficient charge.
- Battery is sulfated or shorted.
- Poor lighting circuit Z1-ground.
- Both headlamp bulbs defective
|
- Clean and secure battery cable clamps
and posts.
- Adjust or replace generator drive belt.
- Test and repair charging system, refer to
Group 8A,
- Test battery state-of-charge,
refer to Group 8A.
- Load test battery, refer to Group 8A.
- Test for voltage drop across Z1-ground
locations, refer to Group 8W..
- Replace both headlamp bulbs.
|
HEADLAMP BULBS BURN
OUT
FREQUENTLY |
- Charging system output too high.
- Loose or corroded terminals or
splices in circuit.
|
- Test and repair charging system, refer to
Group 8A.
- Inspect and repair all connectors and
splices, refer to Group 8W.
|
HEADLAMPS ARE DIM
WITH ENGINE RUNNING
ABOVE IDLE* |
- Charging system output too low.
- Poor lighting circuit Z1-ground.
- High resistance in headlamp
circuit.
- Both headlamp bulbs defective.
|
- Test and repair charging system, refer to
Group 8A.
- Test for voltage drop across Z1-ground
locations, refer to Group 8W.
- Test amperage draw of headlamp circuit.
- Replace both headlamp bulbs.
|
HEADLAMPS FLASH
RANDOMLY |
- Poor lighting circuit Z1-ground.
- High resistance in headlamp
circuit.
- Faulty headlamp switch.
- Loose or corroded terminals or
splices in circuit.
|
- Test for voltage drop across Z1-ground
locations, refer to Group 8W.
- Test amperage draw of headlamp circuit.
Should not exceed 30 amps.
- Replace headlamp switch. Refer to
Group 8E.
- Inspect and repair all connectors and
splices, refer to Group 8W.
|
HEADLAMPS DO NOT
ILLUMINATE |
- No voltage to headlamps.
- No Z1-ground at headlamps.
- Faulty headlamp switch.
- Faulty headlamp dimmer
(multi-function) switch.
- Broken connector terminal or wire
splice in headlamp circuit.
|
- Repair open headlamp circuit, refer to
Group 8W.
- Repair circuit ground, refer to Group 8W.
- Replace headlamp switch. Refer to
Group 8E.
- Replace multi-function switch.
- Repair connector terminal or wire splice.
|
*Canada vehicles must have lamps ON. |
FOG LAMP
CONDITION |
POSSIBLE CAUSES |
CORRECTION |
FOG LAMPS ARE DIM
WITH ENGINE IDLING OR
IGNITION TURNED OFF. |
- Loose or corroded battery cables.
- Loose or worn generator drive
belt.
- Charging system output too low.
- Battery has insufficient charge.
- Battery is sulfated or shorted.
- Poor lighting circuit Z1-ground.
|
- Clean and secure battery cable clamps
and posts.
- Adjust or replace generator drive belt.
- Test and repair charging system. Refer to
Group 8A,
- Test battery state-of -charge. Refer to
Group 8A.
- Load test battery. Refer to Group 8A.
- Test for voltage drop across Z1-ground
locations. Refer to Group 8W.
|
FOG LAMP BULBS BURN
OUT FREQUENTLY |
- Charging system output too high.
- Loose or corroded terminals or
splices in circuit.
|
- Test and repair charging system. Refer to
Group 8A.
- Inspect and repair all connectors and
splices. Refer to Group 8W.
|
FOG LAMPS ARE DIM
WITH ENGINE RUNNING
ABOVE IDLE |
- Charging system output too low.
- Poor lighting circuit Z1-ground.
- High resistance in fog lamp circuit.
|
- Test and repair charging system. Refer to
Group 8A.
- Test for voltage drop across Z1-ground
locations. Refer to Group 8W.
- Test amperage draw of fog lamp circuit.
|
FOG LAMPS FLASH
RANDOMLY |
- Poor lighting circuit Z1-ground.
- High resistance in fog lamp circuit.
- Faulty fog lamp switch.
- Loose or corroded terminals or
splices in circuit.
|
- Test for voltage drop across Z1-ground
locations. Refer to Group 8W.
- Test amperage draw of fog lamp circuit.
- Replace fog lamp switch.
- Inspect and repair all connectors and
splices. Refer to Group 8W.
|
FOG LAMPS DO NOT
ILLUMINATE |
- Blown fuse for fog lamp.
- No Z1-ground at fog lamps.
- Faulty fog lamp switch.
- Broken connector terminal or wire
splice in fog lamp circuit.
- Defective or burned out bulb.
|
- Replace fuse. Refer to Group 8W.
- Repair circuit ground. Refer to Group
8W.
- Replace fog lamp switch.
- Repair connector terminal or wire splice.
- Replace bulb
|
HEADLAMP DELAY MODULE
DELAY FUNCTION INOPERATIVE
(1) Ensure headlamps operate before proceeding.
(2) Remove, inspect and test the HDLP delay 10
amp fuse in junction box. Replace if defective.
(3) With the key off and the connector disconnected,
measure the resistance from the delay module
connector, terminal 4 to vehicle body ground. The
ohmmeter should indicate zero ohms. If not, repair
the open circuit in the wire harness to vehicle body
ground.
(4) With the key on measure the voltage between
the delay module connector, terminal 8 and vehicle
body ground. The voltmeter should indicate battery
voltage. If not, repair the open circuit in the wire
harness from ignition switch to HDLP delay module.
(5) Turn headlamps on and measure voltage at
delay module connector, terminal 6. The voltmeter
should indicate battery voltage. If not repair open circuit
between L2 and HDLP delay module.
(6) Measure the voltage between the delay module
connector, terminal 2 and vehicle body ground. The
voltmeter should indicate battery voltage. If not,
repair the open circuit in the wire harness to the
HDLP fuse in the PDC.
(7) If steps 1 through 6 prove out good, replace
headlamp delay module.
Other materials:
Diagnosis and testing
Trip computer, compass, and
thermometer display module
If the problem with the trip computer, compass,
and thermometer display module is an inaccurate or
scrambled display, use the Self-Diagnostic Test procedures.
If the problem is incorrect display lighting levels,
use a DRB scan tool and th ...