Code
B1373
FIAT
B — Body
Entry illumination relay coil short to positive
Views:
UK: 5
EN: 7
RU: 6
AI status
Completed
Completed
100%
Causes
- Short in the relay coil power feed to battery positive (B+)
- Stuck or welded relay contacts (relay permanently energized)
- Damaged or chafed wiring harness touching a constant 12V source
- Corroded or shorted relay socket or connector
- Faulty Body Control Module (BCM) or lighting control module driving the relay
- Blown or incorrect fuse allowing abnormal circuit conditions
Symptoms
- Entry/interior illumination remains on or cannot be turned off
- Battery drain or discharged battery after vehicle is parked
- Fused circuit blown repeatedly
- Related lighting functions inoperative or behaving erratically
- Malfunction Indicator or body control warning lamp may be present
What to check
- Read live data and freeze frame with scan tool; confirm B1373 stored and any related body codes
- Visually inspect relay, relay socket and wiring harness for damage, corrosion, pin push-out or melted insulation
- Check fuses for the lighting/entry circuit and verify correct fuse rating
- Remove relay and test coil resistance with an ohmmeter; compare to typical relay specs
- With relay removed, measure voltage at the relay coil feed and control pins relative to chassis ground
- Perform a wiggle test on harness while observing voltage and code status
Signal parameters
- Nominal relay coil supply voltage: battery voltage (~12 V) when energized; coil should not be held at B+ when de-energized
- Nominal coil resistance (typical automotive relay): roughly 50–200 ohms (manufacturer spec may vary)
- Typical coil current when energized: ~60–300 mA depending on relay design
- DTC condition: coil feed measures battery voltage (short to +) when command expects low/ground or open
Diagnostic algorithm
- Retrieve DTCs and live data; confirm B1373 and note any related codes. Clear codes and see if B1373 returns.
- Perform a visual inspection of relay, socket and harness near entry illumination components and doors. Repair any obvious damage.
- Remove the entry illumination relay. Inspect pins for corrosion/bridging and test coil resistance with an ohmmeter. Replace relay if coil resistance is open/shorted or out of spec.
- With relay removed, measure voltage at the coil supply terminal and the coil control terminal with ignition ON and with the module commanding off. A constant ~12 V at the supply terminal is normal; a constant 12 V at the coil control terminal when it should be low indicates a short to B+ or a stuck output.
- Probe wiring for continuity to battery positive. Disconnect connectors downstream and upstream to isolate the shorted section. Repair or replace damaged wiring or connectors.
- If wiring and relay check good but coil control point remains at B+, inspect/replace the BCM or lighting control module or update module software per manufacturer service info. Verify module ground integrity before replacement.
- After repairs, reinstall components, clear codes, and perform functional test (operate doors, switch interior lights). Confirm code does not return and check for battery drain over time.
Likely causes
- Shorted feed wire from battery/fuse to the relay coil (insulation damage, pin pushed into harness)
- Failed entry illumination relay (internal short or welded coil)
- Corroded connector at relay socket causing unintended continuity to B+
- BCM output stuck high due to internal failure or software issue
Fault status
Status
Entry illumination relay coil short to positive
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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