Code
B1372
FIAT
B — Body
Entry illumination relay open circuit
Views:
UK: 15
EN: 23
RU: 19
AI status
Completed
Completed
100%
Causes
- Blown fuse for interior/entry illumination circuit
- Failed illumination/entry relay (open coil or contacts)
- Open or damaged wiring between BCM and relay or between relay and lamps
- Corroded or loose relay socket or connector
- Poor or missing ground at relay or lamp circuit
- Wrong or intermittent relay fitment (incorrect relay swapped)
Symptoms
- Entry / courtesy / dome lamps do not turn on when doors open
- Interior illumination remains off or intermittent
- Door-open lamp behavior inconsistent or nonfunctional
- Related switches (door, dimmer) may appear to have no effect
- Possible stored B1372 fault and warning lamp or message depending on vehicle
What to check
- Read and record freeze-frame data and confirmation status with an OBD scanner; clear code and see if it returns
- Visually inspect relevant fuses and fuse holders for the interior/entry lighting circuit
- Inspect the relay physically for signs of damage, overheating or corrosion
- Check relay socket and connector pins for corrosion, bent pins or loose terminals
- Measure battery voltage at relay power terminal and ground continuity at relay ground
- Measure or back-probe the relay control pin while operating the door switches/BCM commands to confirm presence/absence of control signal
Signal parameters
- Battery supply at relay common: approx. 12 V (vehicle battery voltage, may drop to ~11–14 V)
- Relay coil resistance (typical automotive relay): ~50–200 ohms (varies by relay type)
- Expected coil activation signal: 12 V or switched ground from BCM when lamps are commanded
- Relay activation current: typically 50–300 mA for coil, load-side current depends on lamp type
- When activated, continuity between relay common and normally-open contact should be near 0 ohms
Diagnostic algorithm
- Connect a diagnostic scanner, confirm B1372, note freeze-frame and readiness. Clear code and attempt to re-create by opening doors or commanding interior lights.
- Inspect and verify fuses for the entry/illumination circuits; replace if blown and retest. If fuse blows again, suspect short.
- Locate the entry illumination relay and visually inspect relay and socket. Wiggle test relay while operating lamp command; note any change.
- With vehicle battery connected, back-probe relay power terminal to confirm battery feed is present at all times or when accessory on as designed (~12 V).
- Back-probe relay control terminal and operate door/dimmer/lamp command. Verify control signal (either switched 12 V or ground) is present when lamps should activate.
- Check relay ground/return path and continuity from relay output to the interior lamps. Measure for continuity/voltage at lamp connectors with command active.
- Bench-test or swap relay with a known-good identical relay. If swapped relay works, replace faulty relay and retest.
- If relay, fuse and wiring check good but no control signal from BCM, perform BCM I/O tests per factory manual and inspect connector pins for corrosion. Check for related communication codes (e.g., lost comms).
- Repair any damaged wiring, terminals or grounds. After repairs clear codes and verify proper operation through several cycles. If BCM replacement is suspected, follow manufacturer programming and verification procedures.
Likely causes
- Defective relay or relay socket corrosion
- Open wire between BCM and relay control pin
- Blown fuse protecting the relay feed
- Poor ground connection for the lamp/relay circuit
Fault status
Status
Entry illumination relay open circuit detected — relay coil or control circuit continuity/activation failure.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email