B1604

Code

Other B — Body

Lamp Anti-Theft Indicator Circuit Open

Brand: Other

Type: B — Body

Views: UK: 25 EN: 44 RU: 43

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Page language: EN

Causes

Blown fuse for instrument/anti-theft lamps
Burned-out or disconnected lamp (bulb or LED)
Broken, chafed or disconnected wiring between BCM and indicator lamp
Corroded or loose connector at lamp or BCM
Failed BCM/anti-theft module output driver
Aftermarket accessory or previous repair that disturbed the circuit

Symptoms

Anti-theft/immobilizer indicator does not illuminate when system arms/disarms or on ignition
Possible stored body/anti-theft warning lamp DTCs
Security system may still function but without indicator feedback
Intermittent operation if wiring is damaged

What to check

Verify the complaint: does the lamp ever illuminate during key cycles, lock/unlock, or self-test?
Scan for additional DTCs and note freeze frame/occurrence data
Visually inspect the indicator lamp and surrounding trim for loose connectors or damage
Check relevant fuses and relays for continuity and proper fuse rating
Backprobe lamp connector and BCM connector to measure voltages and continuity
Inspect wiring harness along routing for chafe, pinched areas, or rodent damage

Signal parameters

Expected supply voltage: ~12 V battery (or switched 12 V) at lamp fuse when power applied
Expected lamp voltage when driven: 0–12 V depending on lamp type (ground-switched or supply-switched) — typically 12 V when commanded ON
Open-circuit indication: infinite resistance between lamp terminals or 0 V at lamp connector when driver should apply voltage
Bulb filament typical continuity: < 10 ohms (incandescent); LED modules may measure higher or require applied voltage to test
BCM output driver: typically near 0 V (ground sink) when ON if ground-switched, or near battery voltage if supply-switched

Diagnostic algorithm

Verify lamp behavior: cycle ignition, lock/unlock doors and watch indicator. Note when it should illuminate.
Check scan tool data: read B1604, note occurrence count, clear code and see if it returns immediately or after cycling.
Inspect fuses: locate and verify continuity of instrument/anti-theft lamp fuse(s). Replace blown fuse only after diagnosing short/open.
Visual inspection: remove trim to access lamp assembly and connector. Look for disconnected connector, damaged wires or corrosion.
Test lamp: remove lamp from socket and test lamp/LED with a known good 12 V supply or multimeter continuity. Replace if open or nonfunctional.
Measure voltage at lamp connector: backprobe connector with system commanded ON (key on/lock sequence). Verify expected voltage or ground signal. If no voltage, proceed to next step.
Check continuity to BCM: with battery disconnected, measure resistance between lamp connector and BCM output pin per wiring diagram. Open/high resistance indicates wiring/connectors issue.
Wiggle test: with connector connected, have an assistant operate immobilizer while wiggling wiring and connectors to check for intermittent faults.
Inspect and repair wiring: repair chafed wires, replace damaged connector pins, apply dielectric grease and secure harness.
If wiring and lamp are good but no drive signal at BCM: verify BCM power, ground, and related inputs. If BCM output remains inactive or shorted, consider module repair or replacement per manufacturer procedures.
After repair, clear DTCs and verify proper operation through multiple cycles; road test and re-scan to confirm fault resolved.

Likely causes

Open or high-resistance wire(s) between BCM and lamp (most common)
Lamp element failed (filament open or LED failed)
Faulty connector pins (corrosion or pushed out)
BCM output transistor failed (rare compared with wiring/bulb)

Fault status

⚠️ Status

Open circuit detected in the anti-theft indicator lamp circuit. The control module cannot detect the lamp load or expected voltage/continuity. Inspect fuses, lamp element, connectors, and wiring between the lamp and the module; replace or repair as needed. If wiring and lamp are good, the module output driver may be faulty.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-1.5 hours