Code
B13C1
LAND ROVER
B — Body
Fog light - Control switch
Views:
UK: 5
EN: 8
RU: 5
AI status
Completed
Completed
100%
Causes
- Faulty fog light control switch (worn contacts or internal failure)
- Broken, shorted or open wiring between switch and Body Control Module (BCM)
- Poor or corroded connector or ground at switch or BCM
- Blown fuse or failed relay in fog light circuit
- Water ingress or contamination of switch or connectors
- BCM or lighting module software fault or internal failure
Symptoms
- Fog lights will not turn on or off using the dash switch
- Fog light indicator on dash not illuminating or behaves intermittently
- One or both fog lamps not responding while other lights work
- Diagnostic trouble code B13C1 stored and possibly other lighting or communication codes
- Intermittent fog light operation or loss of function after moisture exposure
What to check
- Read and record all stored and pending DTCs with a capable scan tool (check for related U or B codes)
- Verify vehicle symptom: operate fog light switch and observe lamp and dash indicator behavior
- Visual inspection of switch, connectors and wiring for damage, corrosion, water ingress or loose pins
- Check relevant fuses and relays for the fog light circuit and BCM power/ignition supplies
- Check for good ground(s) at switch and BCM (measure
- Backprobe switch connector while operating switch: verify expected voltage or ground signal
Signal parameters
- Supply (Vbatt/ignition) to switch: approx. 9–14 V with ignition on (vehicle dependent)
- Switch output: open/closed continuity or switched ground/12 V depending on vehicle design
- Circuit continuity: near zero ohms between switch contact and BCM input when closed (allow small harness length resistance)
- Expected CAN/LIN message: fog-light switch status present on network when switch operated (check with scan tool)
- When fog lights requested, BCM should energize fog lamp relay circuit to supply ~12 V to lamps
Diagnostic algorithm
- Connect a diagnostic scanner, read and record all codes and freeze frame data. Note related communication codes.
- Confirm the complaint: operate the fog light switch, observe lamps, dash indicator and any change in codes.
- Visually inspect the switch and wiring harness for damage, corrosion or water ingress. Repair obvious issues.
- Check fuses and relays for fog lights and BCM power/IGN supplies; replace suspected faulty items and retest.
- Backprobe the switch connector: verify supply voltage and that the switch changes the expected circuit (voltage to ground or signal level) when operated.
- Check continuity and resistance between switch output pin and BCM input pin with ignition off. Repair open/shorts as needed.
- If equipped, monitor the fog-switch status parameter on the diagnostic tool or scan tool while operating the switch. If the parameter does not change, trace wiring or test BCM input.
- Inspect connectors at the BCM and any intermediate junctions; clean or repair corroded terminals and ensure secure locking.
- If wiring and switch check good, consider bench-testing or swapping the switch with a known-good unit (if available) to confirm switch failure.
- If switch and wiring are confirmed good, suspect BCM input or software. Check for module updates, perform module resets only as recommended, and if necessary, replace or reprogram BCM per manufacturer procedures.
- After repairs, clear codes and verify proper function over a test drive and repeated switch operations.
Likely causes
- Defective fog light control switch
- Wiring/connector fault at switch harness (open, short to ground or Vbatt, corrosion)
- Blown fuse or failed relay supplying the fog light circuit/BCM
- Intermittent/failed communication between switch and BCM (CAN or LIN)
- BCM internal fault (less likely after wiring/switch checks)
Fault status
Status
B13C1 – Fog light control switch fault: switch signal absent, out of range or intermittent. Inspect switch, wiring, connectors and related module communications.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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