B1401

Code

FIAT B — Body

Front left full-open window relay short to ground

Brand: FIAT

Type: B — Body

Views: UK: 14 EN: 9 RU: 19

AI status

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Page language: EN

Front-left window does not operate correctly (stuck, will not fully open)
Window may not respond to switch or behaves intermittently
Related fuse may blow repeatedly
Possible diagnostic trouble lamp or body control message on dash
Other door/window circuits may be affected if shared grounds or harness damage exists

Read and record stored codes and freeze-frame data with a scan tool
Visually inspect relay, relay socket, and front-left door harness for damage, corrosion, or water
Check related fuses and fusible links for continuity and signs of overheating
Unplug relay and inspect connector pins for corrosion, bent pins or debris
Wiggle test wiring while observing window operation and scan data for changes
Backprobe the relay control circuit and measure voltage and continuity with relay removed

Resting (no request): control circuit should be open/high impedance or battery-level depending on design — measure near 12 V or >5 kΩ to ground when disconnected
When module commands full-open: control line should switch (either pull to ground or supply 12 V) — expect a change from resting value to near 0 V or near battery voltage respectively
Short to ground condition: control pin measures near 0 V or very low resistance (
Typical relay coil resistance (general guidance): about 50–200 Ω (varies by relay) — compare to OEM spec if available

Connect a scan tool, read/record code B1401 and any related codes. Note freeze-frame and battery voltage.
Visually inspect the front-left door harness, connector at the door jamb, and relay/socket in the fuse/relay box for damage, corrosion, or moisture. Repair obvious damage.
Locate the front-left full-open relay. With ignition off, remove the relay and inspect pins. Check for corrosion, heat damage, or melted plastic.
With relay removed, measure continuity/resistance between the relay's control pin in the harness and chassis ground. A low resistance (
With harness connector disconnected from the BCM (or relay removed), measure voltage on the control circuit while commanding the window full-open with a scan tool or switch. Verify the control signal changes as expected (see signal params).
If the circuit shows a short to ground, isolate by disconnecting sections of the harness (e.g., door connector at jamb, inline connectors) and re-test to find the short location.
If the wiring and connectors test OK, bench-test or substitute a known-good relay and retest functionality and code status.
If fault persists with wiring and relay verified good, suspect BCM driver failure. Before replacing BCM, verify with scope/backprobe and consult wiring diagram; consider professional module bench test or replacement following OEM programming procedures.
After repair, clear codes and perform several full-open/close cycles to confirm proper operation and that B1401 does not return.

⚠️ Status

Front-left full-open window relay circuit shorted to ground (B1401).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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