Code
B1400
ALFA ROMEO
B — Body
Front left electric window relay short to positive
Views:
UK: 4
EN: 11
RU: 5
AI status
Completed
Completed
100%
Causes
- Short to battery positive on the front left window relay/control wiring
- Faulty front left window relay (stuck closed or internally shorted)
- Faulty Body/Comfort module (ECU) driver transistor or internal fault
- Corroded or damaged connector at the relay, motor, or door harness
- Aftermarket accessory or recent repair altered wiring and created a short
- Water ingress in door or switch assembly causing short to positive
Symptoms
- Front left window does not operate or operates intermittently
- Blown fuse for windows or body electrical circuits
- Constant motor or relay noise even with ignition off
- Other windows or functions affected if fused/shared circuit
- Possible battery drain or parasitic current draw
What to check
- Verify battery voltage and that fuses for windows/body circuits are intact
- Scan vehicle for stored codes and freeze frame/data with a capable scanner
- Visually inspect front left door harness, connectors, and relay for damage or corrosion
- Check for signs of water ingress in the door or switch assembly
- Measure voltage at the relay connector and window motor with switches operated
Signal parameters
- Battery supply voltage at relay fuse (should be ~12–14.5 V with engine running)
- Relay coil/control line voltage (should be low/off when inactive; near battery when shorted)
- Motor supply voltage and ground when window switch is operated
- Current draw through the window motor/relay (compare to known-good values)
- Body ECU output command status for front left window (logical on/off)
Diagnostic algorithm
- Record and clear the DTCs. Reproduce the fault to confirm B1400 returns.
- Inspect fuses and fusible links for the window and body supply circuits; replace any blown fuses only after finding cause.
- With ignition OFF, disconnect the front left window relay and check if the code clears and symptom disappears. If yes, suspect relay or downstream wiring.
- Visually inspect relay socket, relay, and harness for burns, melted insulation, corrosion or water. Replace relay if physically damaged.
- With ignition ON, backprobe the relay connector: check battery feed, control/coil voltage, and ground. A permanent battery-level voltage on the control pin indicates a short to positive.
- If control pin is high with ECU commanding off, disconnect the door harness at the inner door connector and check if the high voltage disappears. Isolate between harness and module.
- If harness removed and control remains high, suspect Body/Comfort module driver fault. If high only with harness connected, inspect harness inside door (bulkhead) and switch/motor for short to positive.
- Perform resistance and continuity checks between relay control pin and module output to locate short; repair chafed wires, damaged insulation, or replace connector/pins as needed.
- If motor is suspected, measure motor current while operating (compare to spec). A seized motor can cause abnormal conditions but usually draws high current rather than short to positive—still inspect motor and switch.
- After repairs, clear codes, operate window through full travel multiple cycles and verify code does not return and no parasitic draw exists.
Likely causes
- Shorted wire between fused battery feed and relay coil/control pin in door harness
- Failed or welded relay contacts feeding the front left window motor
- Body control module output transistor shorted to battery
- Damaged door bulkhead (rubber grommet) chafing the positive feed
- Switch assembly internally shorted to battery positive
Fault status
Status
Front left power window relay/control circuit short to positive voltage detected. Check relay, wiring, connectors, switch and body control module.
Repair difficulty: Medium
Diagnostic time: 1.0 - 2.5 hours
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