Pinpoint Test B: One Low Beam Headlamp Is Inoperative
Headlamps
Pinpoint Tests
Pinpoint Test B: One Low Beam Headlamp Is Inoperative
Refer to Wiring Diagram Set 85, Headlamps/Autolamps for schematic and connector information. Diagrams By Number
Normal Operation
The Lighting Control Module (LCM) is supplied voltage from the Central Junction Box (CJB) for the LH low beam and for the RH low beam on separate circuits. When a request for the low beams is received by the LCM, the LCM provides voltage to the LH and RH headlamps.
This pinpoint test is intended to diagnose the following:
- Fuse
- Wiring, terminals or connectors
- LCM
PINPOINT TEST B: ONE LOW BEAM HEADLAMP IS INOPERATIVE
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
-------------------------------------------------
B1 CHECK FOR VOLTAGE TO THE INOPERATIVE HEADLAMPS
- Ignition OFF.
- Disconnect: Inoperative Headlamp.
- Place the headlamp switch in the HEADLAMPS ON position.
- For Crown Victoria, measure the voltage between the LH headlamp C1021-1, circuit 160 (DB/WH), harness side and ground; or between the RH headlamp C1041-1, circuit 161 (DG/OG), harness side and ground
- For Grand Marquis, measure the voltage between the LH headlamp C1284-1, circuit 160 (DB/WH), harness side and ground; or between the RH headlamp C1285-1, circuit 161 (DG/OG), harness side and ground
- Is the voltage greater than 10 volts?
Yes
REPAIR circuit 57 (BK) for an open. TEST the system for normal operation.
No
GO to B2.
-------------------------------------------------
B2 CHECK FOR VOLTAGE TO THE LCM
- Place the headlamp switch in the OFF position.
- Disconnect: LCM C2145d (LH Headlamp) or C2145c (RH Headlamp).
- Measure the voltage between the LCM C2145d-21 (LH low beam), circuit 1055 (WH/LG), harness side and ground; or between the LCM C2145c-19 (RH low beam), circuit 1056 (DB/LG), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to B3.
No
VERIFY the CJB fuse 19 (10A) or fuse 21 (10A) is OK. If OK, REPAIR circuit 1055 (WH/LG) (LH low beam) or circuit 1056 (DB/LG) (RH low beam) for an open. TEST the system for normal operation. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short. Diagrams By Number
-------------------------------------------------
B3 CHECK THE HEADLAMP VOLTAGE SUPPLY CIRCUIT FOR AN OPEN
- Measure the resistance between the inoperative headlamp, harness side and the LCM, harness side as follows:
- Is the resistance less than 5 ohms?
Yes
GO to B4.
No
REPAIR the circuit in question. TEST the system for normal operation.
-------------------------------------------------
B4 CHECK THE HEADLAMP VOLTAGE SUPPLY CIRCUIT FOR A SHORT TO GROUND
- Measure the resistance between the inoperative headlamp, harness side and ground as follows:
- Is the resistance greater than 10,000 ohms?
Yes
GO to B5.
No
REPAIR the circuit in question. TEST the system for normal operation.
-------------------------------------------------
B5 CHECK FOR CORRECT LCM OPERATION
- Disconnect all the LCM connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the LCM connectors and make sure they seat correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?
Yes
INSTALL a new LCM. REFER to Multifunction Electronic Modules Service and Repair. TEST the system for normal operation.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
-------------------------------------------------