Pinpoint Test D: The Low Beam(s) Are Always On
Headlamps
Pinpoint Tests
Pinpoint Test D: The Low Beam(s) Are Always On
Refer to Wiring Diagram Set 85, Headlamps/Autolamps for schematic and connector information Diagrams By Number.
Refer to Wiring Diagram Set 140, Customer Access for schematic and connector information Diagrams By Number.
Normal Operation
The Smart Junction Box (SJB) sends a voltage signal to the headlamp switch for each headlamp switch position (off, parking lamps and headlamps). At any given time, the headlamp switch routes one of the input circuits to ground. If the SJB detects multiple inputs active or no inputs active for 5 seconds, the SJB turns the parking lamps and headlamps on.
When the SJB detects the headlamp switch in the HEADLAMPS ON position, the SJB provides voltage to the LH and RH low beams.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Headlamp switch
- Body builder equipment
- SJB
PINPOINT TEST D: THE LOW BEAM(S) ARE ALWAYS ON
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
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D1 CHECK THE SJB HEADLAMP SWITCH PIDs
- Enter the following diagnostic mode on the scan tool: SJB DataLogger.
- NOTE: Make sure the headlamp switch is lined up in the correct position when monitoring the PIDs.
- NOTE: Only one PID should indicate ON at each headlamp switch position.
- Monitor the SJB headlamp switch input PIDs (HDLMP_OFF_CKT, HDLMP_PRK_CKT and HDLMP_ON_CKT) while moving the headlamp switch through all positions.
- Do the headlamp switch positions agree with the PIDs?
Yes
GO to D6.
No
GO to D2.
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D2 CHECK FOR VOLTAGE SIGNALS TO THE HEADLAMP SWITCH
- Ignition OFF.
- Disconnect: Headlamp Switch C205.
- Measure the voltage between the headlamp switch, harness side and ground as follows:
- Are the voltages greater than 10 volts?
Yes
GO to D3.
No
GO to D4.
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D3 CHECK FOR VOLTAGE TO THE HEADLAMP SWITCH USING THE CONNECTOR GROUND
- Measure the voltage between the headlamp switch C205-6, circuit CLF23 (WH/VT), harness side and the headlamp switch C205-3, circuit GD114 (BK/BU), harness side.
- Is the voltage greater than 10 volts?
Yes
INSTALL a new headlamp switch. REFER to Headlamp Switch Service and Repair. TEST the system for normal operation.
No
REPAIR circuit GD114 (BK/BU) for an open. TEST the system for normal operation.
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D4 CHECK THE HEADLAMP SWITCH INPUT CIRCUITS FOR A SHORT TO GROUND
- Disconnect: SJB C2280b.
- Measure the resistance between the headlamp switch, harness side and ground as follows:
- Are the resistances greater than 10,000 ohms?
Yes
GO to D5.
No
REPAIR the circuit in question for a short to ground. TEST the system for normal operation.
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D5 CHECK THE HEADLAMP SWITCH INPUT CIRCUITS FOR AN OPEN
- Measure the resistance between the headlamp switch, harness side and the SJB, harness side as follows:
- Are the resistances less than 5 ohms?
Yes
GO to D8.
No
REPAIR the circuit in question for an open. TEST the system for normal operation.
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D6 CHECK THE SJB OUTPUT
- Disconnect: SJB C2280e.
- Does the LH or RH headlamp continue to illuminate?
Yes
For all except stripped chassis, REPAIR circuit CLF04 (BN/BU) (LH headlamp) or circuit CLF05 (BU/GN) (RH headlamp) for a short to voltage as necessary. TEST the system for normal operation.
For stripped chassis, GO to D7.
No
GO to D8.
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D7 ISOLATE THE SHORT TO VOLTAGE
- Disconnect: Body Builder C1010.
- Does the LH or RH headlamp continue to illuminate?
Yes
The vehicle is operating correctly. REFER to the body builder manual to continue diagnosis.
No
REPAIR circuit CLF04 (BN/BU) (LH headlamp) or circuit CLF05 (BU/GN) (RH headlamp) for a short to voltage as necessary. TEST the system for normal operation.
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D8 CHECK FOR CORRECT SJB OPERATION
- Disconnect all the SJB connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the SJB 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 SJB. REFER to Body Control Systems. 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.
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