B1C86

Code

LAND ROVER B — Body

Autolamps lighting switch output relay lamps Inverting

Brand: LAND ROVER

Type: B — Body

Views: UK: 16 EN: 26 RU: 22

AI status

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Page language: EN

Causes

Short or open in the relay control wiring
Faulty autolamps output relay (stuck/inverted contacts)
Poor ground or corroded connector at relay/module
Incorrect or intermittent supply voltage to relay coil
Faulty Body/Lighting Control Module (BCM/LCM) or internal driver circuit
Software/configuration error or recent module reflash/coding issue

Symptoms

Autolamps (automatic headlamps) do not turn on/off as expected
Daytime running lights or headlamps remain on or off incorrectly
Lighting flicker or intermittent operation
Instrument cluster warning for lighting or stored multiple lighting DTCs
Certain lamp functions unresponsive despite switch position

What to check

Read and record all stored codes and freeze frame/vehicle data with a diagnostic tool
Inspect relay, relay socket and harness for corrosion, pin damage, or heat discoloration
Visually inspect wiring from BCM to relay and lamps for chafing, cuts, or modifications
Check for recent repairs or aftermarket accessories on lighting circuits
Verify good battery voltage and main power/ground at BCM and relay

Signal parameters

Expected relay control: logic low (near 0 V) when off and battery voltage (~12 V) when activated for a direct switched output
If PWM control used: duty cycle 0% when off, increased duty when commanded (frequency varies by model)
Typical relay coil current: less than 1 A (measure coil current or resistance against spec)
CAN/Module message: BCM should assert lamp-request bit when autolamps active (verify with OEM scan tool)

Diagnostic algorithm

Connect OEM-level diagnostic tool. Read/record B1C86 plus related codes and live data. Note conditions at time of fault.
Visually inspect relay, relay socket, connector pins and harness to the BCM for damage, corrosion, or loose terminals.
With ignition on and using a multimeter, backprobe the relay control pin at the relay socket. Command autolamps ON/OFF via scan tool and observe voltage: verify it matches expected logic (0 V vs battery).
If control signal is opposite of expected (inverted), swap with a known-good identical relay (if separate) to see if behavior changes.
If relay swap doesn’t change result, backprobe at the BCM connector and inspect wiring continuity and resistance to the relay coil. Check for shorts to ground or battery.
Check module grounds and supply voltages. Wiggle test harness while observing live data to find intermittent connections.
If wiring and relay are good but signal still inverted, reflash or verify BCM software/calibration and check for recent coding changes. Consider replacing BCM only after isolating external faults.
Clear codes and retest under the same conditions to confirm repair.
Safety note: When probing live circuits, follow vehicle manufacturer procedures to avoid airbag/vehicle network disturbances.

Likely causes

Damaged connector or pin corrosion on relay harness
Relay contacts stuck or welded causing reversed output
Short to voltage or ground in the switch output wiring
BCM driver transistor fault

Fault status

⚠️ Status

BCM reports inverted/incorrect polarity on autolamps relay output (lighting switch output relay inverting).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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Browse 332 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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