Code
B1301
FIAT
B — Body
Door electric locking relay coil circuit
Views:
UK: 6
EN: 8
RU: 7
AI status
Completed
Completed
100%
Causes
- Blown fuse for door locking circuit
- Open or shorted wiring in relay coil circuit
- Corroded or loose relay connector or socket
- Failed door-locking relay (coil open or shorted)
- Poor or missing ground at relay coil circuit
- Water ingress or contamination in connector or relay box
Symptoms
- Door locks/unlocks do not operate at one or more doors
- Intermittent locking/unlocking behaviour
- Key fob or central locking switch has no effect for locking circuit
- Clicking noise from relay box may be absent or intermittent
- Interior lock indicator or warning lamp may illuminate or flash
- Possible parasitic battery drain if relay coil is stuck or shorted
What to check
- Visually inspect relay, relay socket and associated connectors for corrosion, bent pins or water damage
- Check relevant fuses (central locking/comfort module) and replace if blown
- With connector disconnected, measure relay coil resistance with a multimeter
- Check supply voltage to relay coil socket (battery voltage present when circuit powered)
- Check control signal from BCM to relay coil (voltage switch or ground switch depending on vehicle design) while commanding locks with scan tool or switch
- Backprobe relay harness to verify continuity between relay socket and BCM pins and to ground
Signal parameters
- Battery/ignition supply to relay coil: ~11–14 V when circuit is powered (varies by vehicle state)
- Relay coil resistance (typical automotive 12 V relay): commonly ~50–200 Ω (manufacturer-specific). An open (>1 MΩ) or near 0 Ω indicates fault
- Control driver behavior: BCM typically grounds or supplies the coil to energize — expect the control terminal to switch close to 0 V (ground-switch) or to battery voltage (supply-switch) when commanded
- Switching behaviour: when relay is commanded, full coil supply should be present and coil current should flow (coil voltage near battery, control terminal near ground or battery depending on design)
Diagnostic algorithm
- Obtain freeze frame and note accompanying body/BCM codes with a scan tool
- Visually inspect relay location, socket, connectors and wiring for damage, corrosion or water ingress; repair visible damage
- Check and replace any blown fuses protecting the central locking/relay circuit
- Backprobe relay socket while operating lock/unlock command: verify battery voltage present at coil supply terminal and that the control terminal changes state (to ground or to +12 V) when commanded
- Measure coil resistance with relay removed: compare to specification or typical range (see signal_params). If coil is open or shorted, replace relay
- If coil and supply look correct, bench-test relay on a bench supply to confirm mechanical/electrical operation
- If relay bench-test is OK, test continuity between relay socket and BCM pins; repair any open or high-resistance circuits
- Check module ground(s) for low resistance to chassis ground (
- If wiring and relay are good but control signal is absent or incorrect, use scan tool to command relay and monitor BCM outputs; if BCM output is not present, suspect BCM driver fault — consult manufacturer guidance before replacing module
- After repairs, clear codes and re-test multiple lock/unlock cycles and verify no reoccurrence; road-test or repeated operation to ensure reliability
Likely causes
- Failed relay coil (open circuit or shorted turns)
- Loose/poor pin contact at relay socket or BCM connector
- Broken wire between BCM and relay coil terminal
- Blown inline fuse protecting relay coil supply
- Ground cable disconnected or high-resistance ground at chassis or module
- Connector corrosion from water entry in door or body harness
Fault status
Status
B1301 — Door electric locking relay coil circuit: relay coil circuit open/short/incorrect voltage detected; door central locking may not operate reliably.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
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