B1C84

Code

LAND ROVER B — Body

Rear light with relay circuit output

Brand: LAND ROVER

Type: B — Body

Views: UK: 19 EN: 25 RU: 29

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Page language: EN

Causes

Blown fuse protecting rear light circuit
Failed rear light relay
Open or shorted wiring between BCM, relay and rear lamp connector
Corroded/loose connector at relay, lamp, or BCM
Failed BCM / driver transistor
Faulty bulb or lamp module (internal short/open)

Symptoms

Rear lights (tail/brake/indicator) do not operate or work intermittently
Warning or message on dash indicating rear light fault
Bulb out or lamp failure messages with bulbs known good
Blown fuse when function is selected
Lights operate only when wiggling harness or after tapping relay

What to check

Read all stored and pending codes on BCM and related modules; note freeze frame/live data
Visually inspect rear lamp assemblies, connectors and wiring for corrosion, water, damage
Check related fuses and fuse holders for continuity and correct rating
Inspect and swap/test the rear light relay with a known good relay (if identical)
Measure voltage at the lamp connector with lamps commanded on (expected battery voltage)
Measure voltage at relay output with relay commanded (battery voltage when on; near 0V off)

Signal parameters

Output voltage at relay contact (when ON): approximately battery voltage (11–15 V)
Output voltage at relay contact (when OFF): near 0 V (open circuit) or floating depending on design
Relay coil resistance (typical): ~50–200 ohms (varies by relay type)
Lamp filament resistance (typical, tail lamp incandescent): tens of ohms; LED modules behave as load with driver electronics
BCM driver output: switched +12 V or switched ground command (check vehicle-specific wiring)
No excessive voltage drop across connectors/wiring when load applied (

Diagnostic algorithm

Use a diagnostic scanner to read and record all BCM and lighting-related codes and live data. Note which rear light output index is flagged.
Visually inspect the rear lamp(s), socket, bulb (or LED module), connectors and wiring for corrosion, water ingress or damage. Repair as needed.
Verify fuses for the rear lighting circuit are intact and make good contact in the fuse box. Replace any blown fuse with correct rating and retest.
With the lighting function commanded ON, measure voltage at the rear lamp positive terminal and ground. If no voltage, trace forward toward relay/BCM.
Inspect/bench-test the relay: remove the relay and energize coil to confirm contacts switch and coil resistance is within spec. Replace relay if faulty.
Backprobe the relay output and relay control feed while commanding the light ON. Confirm relay coil is being driven by the BCM (control voltage present).
Check continuity between relay output and lamp positive terminal; repair any open or high-resistance wiring/connectors.
Measure ground at the lamp negative; confirm continuity to chassis ground and BCM ground. Repair poor grounds.
If wiring and relay are good but no output, test BCM output pin for open/short to supply/ground. If BCM driver is suspect, consult module replacement/reprogramming procedures.
After repairs, clear codes, cycle lights several times and road/test to confirm fault does not return. Re-scan to ensure code is cleared.

Likely causes

Corroded lamp or relay connector causing intermittent contact
Failed relay coil or contact stuck open
Short to ground at lamp or wiring due to chafing/water
Open circuit at lamp filament or connector pins
BCM output transistor degraded (less common)

Fault status

⚠️ Status

Stored when the BCM detects an abnormal condition on the rear light relay output circuit (open, short, out-of-range voltage or inconsistent feedback).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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