Diagnostics and testing of automatic headlights (Discovery 3)

Review

The automatic lighting system only operates when the light switch is set to the Auto position.

For a detailed description of the system design and operation, refer to Section 417-01 "Exterior Lighting" in the Service Station Manual.

Inspection and verification

1. Ensure that the customer's complaint is justified.

2. Visually inspect for obvious electrical problems.

Mechanical factors

Electrical factors

Light switch and its installation Rain/light sensor status and installation Windscreen wiper switch condition and installation

Fuses Battery electrical junction box (BJB) - fuse 15E BJB - fuse 16E BJB - fuse 11E BJB - fuse 25E Central electrical junction box (CJB) - fuse 18P CJB - fuse 67P CJB - fuse 62P Relay Automatic headlight relay Wiring harness Loosening or corrosion of connector(s) Battery Junction Box (BJB) Central Junction Box (CJB) Rain/Light Sensor Control Module LIN electrical circuits (Local interconnect network) CAN electrical circuits (Control Area Network)

3. If an obvious cause for the problem you identified or the customer described is found, resolve it before moving on to further action. (if possible).

4. Use the approved diagnostic system or scan tool to retrieve all diagnostic trouble codes (DTCs) before referring to the symptom chart or DTC index.

Since DTCs are stored in more than one module, a full vehicle data read is recommended.

Clear all DTCs after troubleshooting.

Table of signs of malfunction

Sign of malfunction	Possible reasons	Actions
The parking light(s) and headlight(s) do not operate when the automatic headlight mode is selected.	The fuse(s) have blown The light switch is faulty The windshield wiper switch is faulty Electrical circuit failure Rain/light sensor is faulty LIN electrical circuit failure	Check the fuse(s) (see visual inspection). Check the operation of the light switches and windshield wipers. Check the electrical circuit of the automatic headlights. Refer to the electrical manual. Check for DTCs indicating a malfunction of the rain/light sensor or LIN system.
Automatic headlight switch backlight does not work	The fuse(s) have blown The light switch is faulty Electrical circuit failure Automatic headlight relay failure	Check the fuse(s) (see visual inspection). Check the operation of the light switch. Check the electrical circuit of the automatic headlight relay. Refer to the electrical manual. Check for DTCs indicating a malfunction of the automatic headlights.

DTC Index

NOTE: Generic scan tools cannot read the codes listed or can only read 5-digit codes. Match the 5 digits from the scan tool with the first 5 digits of the listed 7-digit code to identify the fault. (the last 2 digits provide additional information readable by a manufacturer approved diagnostic system).

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DTC codes	Description	Possible reasons	Actions
B1A9801	LIN bus - electrical circuit No.1	LIN bus: short circuit to battery + or ground	Refer to the guided diagnostic program for this code on the approved diagnostic system. The LIN bus provides serial communication with the rain sensor, sunroof, optional seat memory modules, and DTC logging is controlled by the vehicle configuration file (CCF) (depending on the installation). Repair is only required when one or more devices are not installed and are not working properly. See the "Lost Connection" condition description at the beginning of this table.
B1A9881	LIN bus - electrical circuit No.1	Software error Power failure when transmitting rain/light sensor signal	Refer to the guided diagnostic program for this code on the approved diagnostic system. No repair is required unless there is a customer complaint about poor rain sensor, sunroof, or seat memory operation. The LIN bus provides serial communication with the optional rain sensor, sunroof, and seat memory modules, and DTC logging is controlled by the vehicle configuration file (CCF) (depending on the installation). Repair is only required when one or more devices are not installed and are not working properly. See the "Lost Connection" condition description at the beginning of this table.
B1A9883	LIN bus - electrical circuit No.1	LIN bus checksum error	Refer to the guided diagnostic program for this code on the approved diagnostic system. The LIN bus provides serial communication with the rain sensor, sunroof, optional seat memory modules, and DTC logging is controlled by the vehicle configuration file (CCF) (depending on the installation). Repair is only required when one or more devices are not installed and are not working properly. See the "Lost Connection" condition description at the beginning of this table.
B1B551C	Rain sensor module	The rain sensor supply voltage is not normal	Refer to the guided diagnostic routine for this code on the approved diagnostic system. Refer to the electrical guides and check for power to the sensor module from the CJB, repair as necessary. If power is present, no action required, clear/ignore DTC.
B1B5546	Rain sensor module	Rain sensor parameter/calibration memory failure: Initialization error - unable to perform optical calibration	Refer to the guided diagnostic program for this code on the approved diagnostic system. Check the windshield for cleanliness in the sensor installation area. Check that the sensor is installed correctly on the optical element and that the optical element fits tightly to the windshield. Clear the DTC and retest. If the DTC reappears, replace the rain/light sensor.
B1B5549	Rain sensor module	Internal electronic malfunction	Check the rain/light sensor module and electrical circuit. Refer to the electrical manual. If the module is suspected, refer to the warranty policy and procedures manual.
B1B5587	Rain sensor module	No message	Refer to the guided diagnostic program for this code on the approved diagnostic system. The rain sensor is not installed on all models. (custom installation). Registration of the failure is prohibited by the CCF file, but if the CCF file is incorrectly configured, the DTC may be registered by mistake. Repair is only required for vehicles with a sunroof. If necessary, refer to the description of the "Lost Communication" condition at the beginning of the "Communication Systems Module" section.
B1B5591	Rain sensor module	Rain sensor module - the measured temperature is outside the normal operating range.	No action required, clear/ignore DTC.
B1D3713	Wiper Switch Electrical Circuit	Windscreen wiper switch wiring circuit: open circuit	Refer to electrical manuals and check switch circuit. Replace/repair as necessary.
B1C8612	Automatic headlight switch backlight relay output	Automatic headlight switch illumination relay output circuit: short circuit to battery +	Refer to the electrical manuals and check the automatic headlamp switch illumination relay circuit. (if available). Replace/repair if necessary. If no such device is present, check the vehicle configuration. Clear/ignore DTC.
B1C8614	Automatic headlight switch backlight relay output	Automatic headlight switch illumination relay output circuit: short to ground or open circuit	Refer to the guided diagnostic routine for this code on the approved diagnostic system. Refer to the electrical guides and check the fuse and output circuit of the automatic headlamp switch illumination relay. (if available). Replace/repair if necessary. If no such device is present, check the vehicle configuration. Clear/ignore DTC.
B1D4013	Electrical circuit for connecting the light switch	Light Switch Wiring Circuit: Open Circuit	Refer to the guided diagnostic program for this code on the approved diagnostic system. Refer to the electrical guides and check the switch circuit. Replace/repair as necessary.
U1A1449	CAN initialization failure	Internal electronic malfunction	Check the electrical power and ground circuits of the unit. Refer to the electrical manual. Configure the module(s) using the approved diagnostic system. If a module is suspect, refer to the warranty policy and procedures manual.