B1802

Code

Other B — Body

Lamp Turn Signal Rear Output Circuit Failure

Brand: Other

Type: B — Body

Views: UK: 31 EN: 53 RU: 37

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Burned out or faulty rear turn signal bulb
Corroded or loose bulb socket or connector
Open or shorted wiring between bulb socket and BCM
Poor or missing ground at the lamp circuit
Damaged connector, pin, or terminal (water intrusion/mechanical damage)
Failed BCM/lighting control output transistor or driver

Symptoms

Rear turn signal (left or right depending on circuit) does not illuminate
Turn signal warns or dashboard indicator shows incorrect operation
Hyperflashing (rapid turn signal blink) indicating low bulb/load or open circuit
Intermittent rear turn signal operation or works when wiring moved
Lamp-out or fault message displayed on cluster

What to check

Scan module(s) for stored DTCs and freeze frame data; record related codes
Visually inspect rear lamp assembly, bulb, socket, and connector for corrosion, damage, or moisture
Verify correct bulb type and filament integrity by replacing or testing bulb
Inspect wiring harness along route for damage, pinched or rubbed areas and connector corrosion
Check fuses and relays related to lighting circuits
Back-probe or access socket contacts while operating turn signal to measure voltage and waveform

Signal parameters

Expected voltage at socket with turn on: ~11–14 V (vehicle nominal 12 V)
Off voltage at socket: near 0 V (or small parasitic voltage if multiplexed)
Typical incandescent bulb current: 0.5–3 A per filament (varies by vehicle/bulb)
Typical LED lamp current: 0.05–0.5 A (may require load resistor)
Turn signal flash rate: ~60–120 cycles/min (1–2 Hz) for a single output; hyperflash >120 cycles/min may indicate low load/open circuit
If BCM uses PWM output: duty cycle varies; check OEM service data for expected waveform

Diagnostic algorithm

Read and record DTC(s) and erase then re-check to confirm repeatability.
Reproduce the symptom (operate turn/hazard lights) and note which side and whether condition is constant or intermittent.
Visually inspect lamp, socket and connector; replace bulb with known good unit or swap left/right bulb to isolate lamp vs wiring/BCM.
With connector accessible, back-probe the socket and measure voltage to ground while operating the turn signal. Note steady 12 V, pulsed PWM, or no voltage.
If no voltage at socket, check for voltage at wiring near BCM/lighting module. If voltage present near module but not at socket, inspect/repair wiring and connectors between locations.
Check continuity and resistance from lamp socket to BCM output pin with power off; look for opens or high resistance. Also check continuity to chassis ground from lamp negative contact.
If short/high current suspected, measure current draw of circuit (use inline ammeter or clamp meter on supply) to identify short/overload. Remove load (bulb) and see if DTC clears or output returns to normal to confirm load fault.
Inspect and test related fuses, relays, and any trailer/harness splices. Repair/replace damaged wiring or connectors; clean and secure grounds.
If wiring and bulb are good but output still not present or module shows internal fault, consult OEM service data for BCM replacement/testing; consider replacing or reprogramming module only after wiring is confirmed good.
Clear codes and verify repair by cycling turn/hazard lights and road-test as needed.

Likely causes

Failed/incorrect bulb (LED vs incandescent) or high-resistance filament
Corrosion or bent pins in rear lamp connector
Wiring chafe causing intermittent short to chassis or battery
BCM output transistor failed due to overcurrent or water intrusion
Poor ground at body panel/lamphousing causing intermittent operation

Fault status

⚠️ Status

Stored when the body/lighting control detects an open, short, overcurrent, or driver failure on the rear turn signal output circuit; may cause lamp failure or hyperflash.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours