B1355

Code

FIAT B — Body

Ignition on circuit

Brand: FIAT

Type: B — Body

Views: UK: 2 EN: 5 RU: 3

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Blown fuse for ignition/IGN feed
Faulty ignition switch or key cylinder contacts
Stuck or failed ignition relay
Open, short-to-ground or short-to-battery in ignition feed wiring/connector
Corroded, loose or water-damaged connector at BCM/ECU or fusebox
Weak or discharged battery causing undervoltage

Symptoms

No crank / no start or intermittent starting
Accessories, dash cluster or radio may not power with key ON
Warning lamps or communications errors in instrument cluster
Intermittent loss of vehicle electrical functions when key is ON
Possible battery drain or repeated fault storage after clearing codes

What to check

Read freeze frame / freeze data and note conditions when code set (battery voltage, ignition state).
Verify battery state-of-charge and surface charge (should be >12.4 V at rest).
Visually inspect fuses and fusebox for corrosion or heat damage; check related fuse(s).
Check ignition relay operation (listen for click, swap with known-good relay if available).
Measure voltage at ignition switch terminals and at BCM/ECU ignition power pin with key OFF and ON.
Inspect wiring harness and connectors for signs of water ingress, corrosion, chafing, or loose pins (steering column, fusebox, under-dash).

Signal parameters

Battery voltage (rest): ~12.4–12.8 V (healthy),
Ignition ON feed (IGN rail) with key ON: ~11.5–14.5 V (should be near battery voltage)
Voltage drop from battery positive to ignition feed: typically
Cranking voltage should remain above ~9.5 V; large drops indicate poor connections or weak battery
Continuity: ignition switch closed path should show low resistance (
Open-circuit: infinite/OL on continuity check indicates break in circuit; short-to-ground ~0 ohms

Diagnostic algorithm

Record freeze frame, clear codes, and attempt to re-create fault to confirm repeatability.
Verify battery voltage and condition. Charge or replace battery if low and re-test.
With a DVOM, measure battery positive and the ignition feed at the fusebox/relay with key OFF and key ON. Note any unexpected voltage or drops.
Inspect and test the ignition fuse(s) and ignition relay. Replace any suspect fuse/relay and retest.
Probe the ignition switch terminals: verify continuity to the ignition feed with key in ON and that it opens OFF. Replace switch if contacts are intermittent or faulty.
Check wiring and connectors between ignition switch, fusebox and BCM/ECU: look for damaged insulation, pin corrosion, or water ingress. Repair or replace damaged sections and clean connectors.
Measure resistance/continuity from the ignition feed pin at the BCM/ECU back to the fuse/relay. Repair any opens or high-resistance joints.
If wiring and components test good, monitor the ignition feed while operating accessories and cranking to detect voltage drops under load. Address poor grounds or high resistance connections.
If circuit wiring and supply are verified and the fault persists, consider module-level diagnostics: check BCM/ECU power/ground pins and communications. Replace module only after ruling out wiring and supply faults.
After repairs, clear codes and perform a road/start cycle to confirm the fault does not return. Document repair and any parts replaced.

Likely causes

Intermittent open in IGN feed at fusebox or ignition switch
Corroded spade terminal or green/black connector at BCM providing poor contact
Blown or partially blown fuse (thermal/electrical degradation)
Ignition relay coil contacts sticking or intermittent
Wiring harness damage near hinge, steering column or engine bay (pinch/abrasion)
Battery terminal corrosion causing voltage drop

Fault status

⚠️ Status

Ignition ON circuit — the control module has detected an abnormal condition on the ignition supply/wake circuit (open, short, intermittent or incorrect voltage) with key ON.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 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