Diagnostics and testing of rear fog lights (Discovery 3)

Inspection and verification

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

2. Visually inspect for obvious mechanical and electrical problems.

Mechanical factors	Electrical factors
Condition and installation of rear fog lights Lamp holders and installation Lamps and installation Fog light switch condition and installation	Fuses Battery electrical junction box (BJB) - fuse 2E BJB - fuse 11E Central electrical junction box (CJB) - fuse 28P CJB - fuse 44P Wiring harness Loosening or corrosion of connector(s) Fog light relay Fog light indicator lamp Fog light switch Battery Junction Box (BJB) Central Junction Box (CJB)

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
Fog lights not working	Lamp failure The fuse(s) have blown Electrical circuit failure The switch does not work	Check the lamp condition. Check the fuse(s) (see visual inspection). Check the fog lamp circuits. Check the switch operation. Refer to the electrical manual.
Adjusting the brightness of fog lights	Incorrect lamp power Electrical circuit failure Switch malfunction	Check the condition and power of the lamp. Check the electrical circuits of the fog lights. Check the operation of the switch. Refer to the electrical equipment manual.
The control lamp does not work	The fuse(s) have blown The switch does not work Electrical circuit failure Instrument cluster malfunction	Check the fuse(s) (see visual inspection). Check the switch operation. Check the test lamp circuits. Refer to the electrical manual. Check for diagnostic trouble codes (DTCs) indicating a malfunction in the instrument cluster.

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
B1A7964	Rear fog lights	Lack of signal credibility	Check the instrument cluster and electrical circuits. Refer to the electrical equipment manual.
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.