B1B37

Code

Generic B — Body

Body Control Module (BCM) — Interior Lighting Circuit Fault

Brand: Generic

Type: B — Body

Views: UK: 12 EN: 15 RU: 11

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or shorted wiring in interior lighting circuit
Poor or corroded ground or power connection to BCM or lamps
Blown fuse or faulty relay for interior lamps
Failed BCM output driver or internal circuitry
Faulty dimmer/switch or lamp module (including LED drivers)
Faulty or incompatible aftermarket accessory tied into interior lighting

Symptoms

Interior dome/map/reading lights do not turn on
Lights stuck on or intermittently switching
Interior lights dim, flicker, or are uneven
Related fuses blow repeatedly
Battery drain with vehicle off (parasitic draw)
Instrument cluster or dash illumination affected

What to check

Retrieve freeze-frame and all stored BCM and network codes with a scan tool
Visually inspect interior lamp sockets, bulbs/LEDs, wiring harnesses, and connectors for damage or corrosion
Check relevant fuses and relays for continuity and correct rating
Verify BCM power supply and ground voltages at the connector
Backprobe the BCM output pin for the affected lamp while operating the light control
Wiggle test connectors and harnesses while observing lights and live data for intermittency

Signal parameters

Vehicle battery voltage at BCM: ~11–14.5 V (key on / engine running range)
BCM output high (lamp on): near battery voltage (~11–14 V)
BCM output low (lamp off): ~0 V (or within a few hundred millivolts)
Expected circuit resistance (front harness to lamp): typically < 5 ohm (varies by design)
Expected current per incandescent lamp: ~0.1–3 A (varies by lamp); LED circuits: typically tens to a few hundred mA
PWM dimming (if used): frequency commonly 100–1000 Hz (manufacturer-specific)

Diagnostic algorithm

Connect a diagnostic scanner and read all stored/ pending codes and live data for BCM and body network. Note freeze-frame and related codes.
Visually inspect lamps, sockets, harnesses, connectors, and associated fuses/relays. Repair obvious damage or corrosion.
With battery voltage known, backprobe the BCM power and ground pins to confirm stable supply and good ground (11–14.5 V and near 0 V respectively).
Operate the interior lights and measure voltage at the BCM output pin for the affected circuit. Confirm expected high/low switching or PWM signal.
If output is correct at the BCM but lights do not behave, measure voltage at the lamp socket to find where voltage is lost — isolate wiring between BCM and lamp.
If output is abnormal (stuck, floats, or shows short) disconnect the lamp/load and re-test output. If fault clears with load disconnected suspect short in harness or damaged lamp/LED driver.
Perform a current draw test on the circuit (with lamps on and off) to detect excessive load or short to ground. Replace faulty lamp or remove aftermarket loads if present.
Inspect and repair connectors or wiring found damaged. Clean corroded connectors and secure grounds.
If wiring and lamps test good but BCM output remains faulty, confirm software/calibration status and check for technical service bulletins. Reprogram or update BCM software if recommended.
As a last step, bench-test or replace the BCM (follow manufacturer procedures for module programming and immobilizer/security handling). After repairs, clear codes and verify proper operation and that code does not return.

Likely causes

Loose ground at BCM or body harness causing intermittent circuit
Short to battery (constant 12V) or short to ground on an output wire
Failed LED driver module or burned-out incandescent bulb drawing abnormal current
Connector corrosion inside door/junction harness
BCM output transistor/driver failed (common on modules that directly drive LEDs)

Fault status

⚠️ Status

BCM detected interior lighting circuit fault (open/short/high resistance or driver failure). Stored when output behavior or circuit parameters are outside expected limits.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours