Code
B1337
ALFA ROMEO
B — Body
Rear door open circuit
AI status
Completed
Completed
100%
Causes
- Faulty rear door ajar/latch switch or sensor
- Open, broken or pinched wiring in the door harness (common at hinge area)
- Corroded or loose connector at door jamb or BCM
- Short to power or to ground in the circuit
- Poor ground at BCM or related ground strap
- Water intrusion in door connector or latch assembly
Symptoms
- Rear door open warning lamp or message on dash
- Interior/dome light may stay on or not operate correctly
- Central locking or alarm may not arm or may trigger falsely
- Possible battery drain if light stays on
- Inconsistent door status in scan tool data
- Malfunction indicator (DTC) stored and may reappear after clearing
What to check
- Connect a diagnostic scanner and read live data for rear door status while opening/closing the door
- Visually inspect door hinge area wiring for abrasion, pinching or breaks
- Inspect and unplug door connector; check for corrosion, bent pins, water ingress
- Measure voltage at the switch connector with door open and closed
- Check continuity between the switch and BCM input pin with harness disconnected (wiring continuity)
- Check ground continuity from BCM ground to chassis and door ground points
Signal parameters
- Type: Discrete/digital switch input (door-ajar sensor)
- Expected behavior: signal toggles between Low (closed/ground) and High (open/pull-up to battery or module supply).
- Typical voltages (manufacturer dependent): door closed ≈ 0–1 V (grounded); door open ≈ battery voltage (~9–14 V) or module logic high (~5 V).
- Continuity: closed switch ≈ near 0 Ω; open switch ≈ OL/infinite Ω.
- Current draw: negligible (logic input); no heavy load expected on the circuit.
Diagnostic algorithm
- Verify DTC B1337 with an OBD/diagnostic scanner and record freeze-frame/live data showing rear door status.
- Reproduce symptom: open and close rear door while watching live data to confirm the input does not change properly.
- Visually inspect the rear door wiring harness, especially at the hinge/boot area, for damage or chafing.
- Disconnect the rear door connector and inspect terminals for corrosion, bent pins or water. Repair/clean as required.
- With harness disconnected, check continuity between the door switch contacts (or latch) and the BCM input pin using wiring diagrams to identify pins.
- Measure voltage at the BCM side connector while operating the door: confirm expected high/low transitions. If no transition at BCM but present at switch, suspect wiring open between them.
- If wiring and switch test OK, test/replace the rear door latch/sensor assembly and recheck system operation.
- If replacement of switch/latch and wiring repair do not fix the issue, check BCM grounds and then consider BCM input failure; consult manufacturer wiring diagrams and consider module reprogramming or replacement as last resort.
- After repairs, clear codes, cycle doors multiple times and road/test to confirm no reoccurrence.
Likely causes
- Wiring damaged at door hinge (most common)
- Failed door latch/ajar switch
- Corroded/pushed-out terminal in door connector
- Water-damaged latch assembly or connector
- Faulty BCM input (least common)
Fault status
Status
Rear door open circuit detected — the body control module is reporting an open or abnormal signal on the rear door switch circuit.
Repair difficulty: Medium
Diagnostic time: 0.5 - 2.0 hours
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Repair manuals
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89
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