Code
B1300
ALFA ROMEO
B — Body
Door electric locking relay coil circuit
Views:
UK: 8
EN: 10
RU: 9
AI status
Completed
Completed
100%
Causes
- Open or short in relay coil supply or return wiring
- Corroded, loose or damaged relay connector or socket
- Faulty door lock relay (coil open/short or intermittent)
- Blown fuse or poor fuse connection in relay supply circuit
- Poor ground or battery supply to relay/BCM
- Body Control Module (BCM) output driver fault or software error
Symptoms
- Central locking does not operate or operates intermittently
- No audible relay click when locking/unlocking
- Only some doors lock/unlock
- Dashboard message or indicator about central locking error
- Parasitic battery drain (rare) or fuse blowing
- Remote key fob locking/unlocking ineffective or inconsistent
What to check
- Read stored and pending codes with a diagnostic scanner; check BCM for related body/CAN errors
- Visually inspect relay, relay socket, fuses and associated connectors for corrosion, heat damage or loose pins
- Check fuse continuity and supply voltage to relay fuse
- Listen for relay click while commanding locks from scanner or key fob
- Measure voltage at relay coil supply and control pins during lock/unlock command
- Measure coil resistance (relay removed) and compare with expected range
Signal parameters
- Relay coil supply voltage (key ON): typically battery voltage ≈ 12 V
- Control signal when activating: BCM usually grounds coil — control pin should go to ~0 V when active; inactive ≈ 12 V
- Typical relay coil resistance: approx. 60–200 ohms (manufacturer-dependent) — expect coil current roughly 60–200 mA at 12 V
- Activation duration: brief pulses during lock/unlock (usually < 2 seconds)
- Fuse rating: check vehicle-specific manual (commonly 7.5 A–20 A for body circuits)
Diagnostic algorithm
- Confirm B1300 is current or stored; note freeze-frame and related codes from BCM.
- Visual inspection: check relay, socket, fuses and wiring for corrosion, damage or water ingress. Repair obvious issues.
- With key ON, command lock/unlock while listening for relay. If no click, proceed to electrical checks.
- Check fuse supplying the relay for continuity and battery voltage at both sides of the fuse.
- Remove relay and measure coil resistance across coil pins on the relay. If outside expected range, replace relay.
- With relay removed, measure supply voltage at the relay supply terminal (should be ~12 V) and monitor the control terminal while commanding locks. Control should switch to ~0 V (or change state) when activated.
- If supply present but no control change, backprobe connector and test continuity between BCM output and relay socket; check for shorts to battery or ground.
- If wiring and connectors are good and BCM output does not change, inspect BCM grounds and power. If BCM output is confirmed faulty, consider BCM repair/replacement and check for software updates.
- If intermittent, perform wiggle tests on harnesses while operating locks; repair broken wires or poor crimps with solder or proper connectors.
- After repair, clear codes and test multiple lock/unlock cycles; confirm no new B1300 or related codes appear.
Likely causes
- Faulty relay or relay socket (most common)
- Wiring/connectors to relay open or corroded
- Blown fuse or poor supply to the relay
- BCM driver fault (less common) or intermittent grounding
- Aftermarket alarm or actuator causing short/overload
Fault status
Status
Door electric locking relay coil circuit fault — open/short or relay/BCM drive issue detected.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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