Code
B1500
ALFA ROMEO
B — Body
Left turn indicator warning lamp open circuit
Views:
UK: 3
EN: 9
RU: 6
AI status
Completed
Completed
100%
Causes
- Burnt or open left front/rear turn signal bulb (filament broken)
- Open or disconnected connector at lamp or harness
- Corroded or damaged wiring (broken conductor, chafing)
- Faulty ground for the lamp circuit
- Blown fuse or faulty relay in the lighting circuit
- Faulty instrument cluster or lamp monitoring module
Symptoms
- Left turn indicator warning lamp in dash does not illuminate or does not flash
- Turn signal left side does not operate or is not recognized by the cluster
- Possible message or warning on dash indicating lamp failure
- Turn signals may still function on other side
- Possible rapid flash or hyperflashing if bulb load mismatch (with LED retrofit)
What to check
- Visually inspect left turn bulbs and lamp sockets for broken filaments, corrosion, or damage
- Verify fuse(s) and related relays for the lighting circuit
- Check connector engagement and condition at lamp and instrument cluster
- Scan vehicle for additional related DTCs and lamp-monitoring messages
- With turn signal ON, measure voltage at lamp connector for pulsed supply
- Perform continuity/ohms check from cluster connector to lamp connector
Signal parameters
- Turn-signal supply: pulsed 0–12 V square wave at turn signal rate (~1–2 Hz) when left indicator is active
- Lamp filament resistance (approx): small incandescent turn lamp ~2–30 ohms depending on lamp type (LEDs differ significantly)
- Open-circuit condition: no pulsed voltage present at lamp connector or infinite resistance to cluster pin
- Ground continuity: near 0 ohms between lamp ground and chassis (typically
Diagnostic algorithm
- Retrieve freeze frame and related codes with a scanner; note if code is current or historic.
- Visually inspect left front and left rear turn lamps and sockets. Replace bulb if filament is broken or lamp is obviously faulty.
- Operate left turn signal and observe dash indicator and exterior lamps. Note which lamp(s) do not illuminate.
- With a DVOM, backprobe the lamp power pin at the socket while signalling left: confirm pulsed 12 V is present. If present, check lamp/filament resistance or replace lamp.
- If no pulsed voltage at socket, check continuity between the cluster/turn module output pin and lamp socket. Repair any open wiring or connector faults found.
- Check ground at lamp housing: measure continuity to chassis and voltage drop under load. Repair ground if excessive resistance.
- Inspect and test fuse(s) and any turn-signal/relay modules in the circuit; replace if faulty.
- If wiring and lamps are good, check the instrument cluster or lamp monitoring module inputs. Test cluster outputs for proper signaling and replace/repair cluster only after wiring verified.
- After repairs, clear codes and perform a functional test by operating the left turn signal and re-scan for return of the code.
Likely causes
- Failed/removed bulb or broken filament
- Open wiring or disconnected lamp connector
- Corroded lamp holder or poor ground
- Faulty instrument cluster input or lamp monitoring circuit
Fault status
Status
B1500 — Left turn indicator warning lamp open circuit detected (lamp not detected by cluster).
Repair difficulty: Medium
Diagnostic time: 0.5 - 2.0 hours
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