Code
B1371
ALFA ROMEO
B — Body
Interior courtesy light relay circuit
Views:
UK: 6
EN: 10
RU: 5
AI status
Completed
Completed
100%
Causes
- Blown fuse for interior lighting or relay coil supply
- Faulty interior courtesy light relay (stuck open/closed or intermittent)
- Damaged wiring harness (open, short to battery, short to ground) in relay supply or output circuits
- Poor or corroded connector contacts at relay, light assemblies or BCM
- Faulty BCM or lighting module (incorrect drive or feedback)
- Shorted or burnt interior light assembly or switch
Symptoms
- Interior/courtesy lights do not illuminate when doors are opened
- Lights remain on and do not turn off
- Intermittent operation of interior lights
- Other body electrical features controlled by the same BCM may show faults
- Related fuse may blow repeatedly
What to check
- Verify fuse(s) for interior lighting and relay coil are intact
- Listen for relay click when doors are opened or when interior lighting is commanded
- Inspect relay socket and connectors for corrosion, heat damage or loose pins
- Check for voltage at relay supply terminal with ignition on and door-open command
- Measure continuity and resistance of relay coil and switch contacts (relay removed)
- Scan BCM for additional related DTCs and monitor courtesy light outputs
Signal parameters
- Relay supply voltage: nominal battery voltage (~11–14.5 V) at relay supply terminal
- Relay coil resistance (typical automotive small relay): approx. 60–200 Ω (manufacturer dependent)
- Switched output: ~12 V when relay contacts closed; near 0 V when open (load dependent)
- Control signal from BCM: either ground-switched or +12 V-switched to the relay coil depending on design
- Expected behavior: relay coil energized when interior lights commanded ON (door open or interior switch), de-energized when OFF
Diagnostic algorithm
- Retrieve freeze frame and full scan of BCM to confirm B1371 and check for related codes.
- Visually inspect fusebox and relays for signs of damage, replace any suspect fuses/relays with known-good units.
- With ignition and doors in the appropriate states, backprobe relay socket to confirm presence of battery feed and correct control signal from BCM.
- If relay supply is missing, trace supply back to fuse and battery terminal; repair any open circuit.
- If supply present but control signal absent or incorrect, test BCM output wiring for continuity to relay coil; repair any open/short.
- Remove relay and bench-test coil for correct resistance and proper contact switching. Replace relay if coil open or contacts fail.
- If relay bench-tests OK but circuit still faults, inspect and test the courtesy light wiring and grounds; repair any corrosion or poor ground.
- If wiring and relay are good, perform BCM output activation tests (using scan tool to command light on/off while monitoring relay control) and, if suspect, consult manufacturer procedures for BCM testing and replacement.
- After repairs, clear DTC(s) and verify correct operation through repeated door-open/close cycles and scan tool monitoring.
Likely causes
- Relay failure (mechanical or coil open/intermittent)
- Loose/corroded connector at relay socket or BCM
- Broken wire on the switched feed or ground to the courtesy light circuit
- Defective BCM output transistor driving the relay coil
Fault status
Status
Interior courtesy light relay circuit fault detected — check relay, supply, control circuit and BCM.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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Code
B1371
FIAT
B — Body
Interior courtesy light relay circuit
Views:
UK: 8
EN: 9
RU: 5
AI status
Completed
Completed
100%
Causes
- Blown fuse for interior lighting or relay coil supply
- Faulty interior courtesy light relay (stuck open/closed or intermittent)
- Damaged wiring harness (open, short to battery, short to ground) in relay supply or output circuits
- Poor or corroded connector contacts at relay, light assemblies or BCM
- Faulty BCM or lighting module (incorrect drive or feedback)
- Shorted or burnt interior light assembly or switch
Symptoms
- Interior/courtesy lights do not illuminate when doors are opened
- Lights remain on and do not turn off
- Intermittent operation of interior lights
- Other body electrical features controlled by the same BCM may show faults
- Related fuse may blow repeatedly
What to check
- Verify fuse(s) for interior lighting and relay coil are intact
- Listen for relay click when doors are opened or when interior lighting is commanded
- Inspect relay socket and connectors for corrosion, heat damage or loose pins
- Check for voltage at relay supply terminal with ignition on and door-open command
- Measure continuity and resistance of relay coil and switch contacts (relay removed)
- Scan BCM for additional related DTCs and monitor courtesy light outputs
Signal parameters
- Relay supply voltage: nominal battery voltage (~11–14.5 V) at relay supply terminal
- Relay coil resistance (typical automotive small relay): approx. 60–200 Ω (manufacturer dependent)
- Switched output: ~12 V when relay contacts closed; near 0 V when open (load dependent)
- Control signal from BCM: either ground-switched or +12 V-switched to the relay coil depending on design
- Expected behavior: relay coil energized when interior lights commanded ON (door open or interior switch), de-energized when OFF
Diagnostic algorithm
- Retrieve freeze frame and full scan of BCM to confirm B1371 and check for related codes.
- Visually inspect fusebox and relays for signs of damage, replace any suspect fuses/relays with known-good units.
- With ignition and doors in the appropriate states, backprobe relay socket to confirm presence of battery feed and correct control signal from BCM.
- If relay supply is missing, trace supply back to fuse and battery terminal; repair any open circuit.
- If supply present but control signal absent or incorrect, test BCM output wiring for continuity to relay coil; repair any open/short.
- Remove relay and bench-test coil for correct resistance and proper contact switching. Replace relay if coil open or contacts fail.
- If relay bench-tests OK but circuit still faults, inspect and test the courtesy light wiring and grounds; repair any corrosion or poor ground.
- If wiring and relay are good, perform BCM output activation tests (using scan tool to command light on/off while monitoring relay control) and, if suspect, consult manufacturer procedures for BCM testing and replacement.
- After repairs, clear DTC(s) and verify correct operation through repeated door-open/close cycles and scan tool monitoring.
Likely causes
- Relay failure (mechanical or coil open/intermittent)
- Loose/corroded connector at relay socket or BCM
- Broken wire on the switched feed or ground to the courtesy light circuit
- Defective BCM output transistor driving the relay coil
Fault status
Status
Interior courtesy light relay circuit fault detected — check relay, supply, control circuit and BCM.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
Similar codes
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Code
B1371
Other
B — Body
Illuminated Entry Relay Circuit Failure
Views:
UK: 15
EN: 21
RU: 14
AI status
Completed
Completed
100%
Causes
- Blown fuse for interior lighting or relay coil supply
- Faulty interior courtesy light relay (stuck open/closed or intermittent)
- Damaged wiring harness (open, short to battery, short to ground) in relay supply or output circuits
- Poor or corroded connector contacts at relay, light assemblies or BCM
- Faulty BCM or lighting module (incorrect drive or feedback)
- Shorted or burnt interior light assembly or switch
Symptoms
- Interior/courtesy lights do not illuminate when doors are opened
- Lights remain on and do not turn off
- Intermittent operation of interior lights
- Other body electrical features controlled by the same BCM may show faults
- Related fuse may blow repeatedly
What to check
- Verify fuse(s) for interior lighting and relay coil are intact
- Listen for relay click when doors are opened or when interior lighting is commanded
- Inspect relay socket and connectors for corrosion, heat damage or loose pins
- Check for voltage at relay supply terminal with ignition on and door-open command
- Measure continuity and resistance of relay coil and switch contacts (relay removed)
- Scan BCM for additional related DTCs and monitor courtesy light outputs
Signal parameters
- Relay supply voltage: nominal battery voltage (~11–14.5 V) at relay supply terminal
- Relay coil resistance (typical automotive small relay): approx. 60–200 Ω (manufacturer dependent)
- Switched output: ~12 V when relay contacts closed; near 0 V when open (load dependent)
- Control signal from BCM: either ground-switched or +12 V-switched to the relay coil depending on design
- Expected behavior: relay coil energized when interior lights commanded ON (door open or interior switch), de-energized when OFF
Diagnostic algorithm
- Retrieve freeze frame and full scan of BCM to confirm B1371 and check for related codes.
- Visually inspect fusebox and relays for signs of damage, replace any suspect fuses/relays with known-good units.
- With ignition and doors in the appropriate states, backprobe relay socket to confirm presence of battery feed and correct control signal from BCM.
- If relay supply is missing, trace supply back to fuse and battery terminal; repair any open circuit.
- If supply present but control signal absent or incorrect, test BCM output wiring for continuity to relay coil; repair any open/short.
- Remove relay and bench-test coil for correct resistance and proper contact switching. Replace relay if coil open or contacts fail.
- If relay bench-tests OK but circuit still faults, inspect and test the courtesy light wiring and grounds; repair any corrosion or poor ground.
- If wiring and relay are good, perform BCM output activation tests (using scan tool to command light on/off while monitoring relay control) and, if suspect, consult manufacturer procedures for BCM testing and replacement.
- After repairs, clear DTC(s) and verify correct operation through repeated door-open/close cycles and scan tool monitoring.
Likely causes
- Relay failure (mechanical or coil open/intermittent)
- Loose/corroded connector at relay socket or BCM
- Broken wire on the switched feed or ground to the courtesy light circuit
- Defective BCM output transistor driving the relay coil
Fault status
Status
Interior courtesy light relay circuit fault detected — check relay, supply, control circuit and BCM.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
Similar codes
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