Pinpoint Test D: The Low Beam(s) Are Always On
Headlamps
Pinpoint Test D: The Low Beam(s) Are Always On
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 (Smart Junction Box) detects multiple inputs active or no inputs active for 5 seconds, the SJB (Smart Junction Box) turns the parking lamps and headlamps on.
When the SJB (Smart Junction Box) detects the headlamp switch in the HEADLAMPS ON position, the SJB (Smart Junction Box) 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 (Smart Junction Box)
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.
D1 CHECK THE SJB (Smart Junction Box) HEADLAMP SWITCH PIDs
- Enter the following diagnostic mode on the scan tool: SJB (Smart Junction Box) 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 (Smart Junction Box) 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.
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:
Headlamp Switch Connector-Pin Circuit C205-6 CLF23 (WH/VT) C205-2 CLS34 (GY) C205-7 CLF18 (BU/WH)
Are the voltages greater than 10 volts?
Yes
GO to D3.
No
GO to D4.
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.
D4 CHECK THE HEADLAMP SWITCH INPUT CIRCUITS FOR A SHORT TO GROUND
- Disconnect: SJB (Smart Junction Box) C2280B.
- Measure the resistance between the headlamp switch, harness side and ground as follows:
Headlamp Switch Connector-Pin Circuit C205-6 CLF23 (WH/VT) C205-2 CLS34 (GY) C205-7 CLF18 (BU/WH)
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.
D5 CHECK THE HEADLAMP SWITCH INPUT CIRCUITS FOR AN OPEN
- Measure the resistance between the headlamp switch, harness side and the SJB (Smart Junction Box), harness side as follows:
Headlamp Switch Connector-Pin SJB (Smart Junction Box) Connector-Pin Circuit C205-6 C2280B-47 CLF23 (WH/VT) C205-2 C2280B-31 CLS34 (GY) C205-7 C2280B-30 CLF18 (BU/WH)
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.
D6 CHECK THE SJB (Smart Junction Box) OUTPUT
- Disconnect: SJB (Smart Junction Box) 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.
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.
D8 CHECK FOR CORRECT SJB (Smart Junction Box) OPERATION
- Disconnect all the SJB (Smart Junction Box) connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the SJB (Smart Junction Box) 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 (Smart Junction Box). 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.