B1A79

Code

LAND ROVER B — Body

Rear fog lamp circuit

Brand: LAND ROVER

Type: B — Body

Views: UK: 15 EN: 26 RU: 22

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Page language: EN

Causes

Blown rear fog lamp bulb
Blown fuse or tripped circuit breaker for rear lamps
Open or corroded connector or wiring (damaged insulation, broken wire)
Short to ground or short to battery in the lamp feed or return
Faulty body control module (BCM) / lamp driver or internal relay
Poor ground at chassis or body ground point

Symptoms

Rear fog lamp does not illuminate when selected
Intermittent rear fog lamp operation
Warning or message on cluster about lamp failure
Blown fuse after attempting lamp activation
Possible other lighting anomalies if BCM output affected

What to check

Visually inspect rear fog lamp bulb and socket for corrosion or damage
Check/re-seat connectors at the rear fog lamp and body harness
Verify relevant fuses and relays are intact and correctly seated
Use a scan tool to read the fault code and check live data/command for rear fog output
Perform a voltage check at the lamp connector with switch ON (supply pin and ground)
Inspect body ground points for corrosion and tighten if loose

Signal parameters

Supply voltage at lamp connector when ON: ~11–14 V
Open-circuit at lamp connector if bulb removed or wire broken: OL (infinite Ω)
Typical bulb resistance (cold) for 21 W lamp: ~6–8 Ω (current ~1.7–2.0 A at 12 V)
Short to ground: near 0 Ω between feed and ground when circuit fused
PWM control (if used by vehicle): check frequency in service manual (commonly 50–200 Hz) and duty indicating commanded brightness

Diagnostic algorithm

Verify the complaint and confirm the B1A79 code with a scan tool; record freeze frame/live data.
Turn the rear fog switch ON and check whether the cluster/BCM shows a commanded output for rear fog lamp.
Visually inspect lamp, socket and wiring harness for obvious damage or corrosion; dry and clean if wet.
Remove lamp bulb and inspect filament; if any doubt, replace with a known-good bulb or test bulb resistance with a multimeter.
Check the fuse and relay for the rear lamp circuit; replace if blown and retest. If fuse blows again, do not continue without locating short.
With power OFF, backprobing: measure continuity and resistance between lamp positive terminal and BCM output; verify ground continuity between lamp ground and chassis ground.
With power ON and someone operating the switch, measure voltage at the connector feed pin. If no feed voltage but BCM commands output, suspect wiring open between BCM and lamp. If no command from BCM, investigate switch, wiring to BCM, and BCM inputs.
If supply voltage present at connector but lamp does not light, verify bulb socket continuity and ground. If OK, measure current draw; excessive current indicates short or faulty lamp; zero/low current indicates open circuit or poor contact.
If wiring and lamp check good, perform injector/driver (BCM) output test per manufacturer procedure — may require module bench test or replacement if driver is faulty.
After repairs, clear codes and perform a function test and road verification; confirm no reoccurrence of the DTC.

Likely causes

Failed bulb or corroded bulb contacts
Blown fuse or poor fuse/relay connection
Corroded/damaged wiring or connector at rear lamp
Faulty lamp driver in BCM (less common)

Fault status

⚠️ Status

Rear fog lamp circuit fault detected (open/short/high resistance or driver fault).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5 - 1.5 hours

Similar codes

Repair manuals

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