B1404 — Front left electric window lowering switch open circuit

Causes

• Open or broken wiring between the switch and body control module (BCM) / motor.
• Faulty front left window lowering switch (internal open contacts).
• Corroded or poorly seated connector at the switch or BCM.
• Water ingress or physical damage to the switch assembly.
• Faulty BCM or module input circuit (less common).
• Aftermarket electrical work or previous repairs that cut or damaged the circuit.

Symptoms

• Front left window will not lower (may or may not raise).
• No action or intermittent action when pressing the front left lowering switch.
• DTC B1404 set and stored in the vehicle control module.
• Switch illumination may be inoperative or intermittent.
• Other window functions (other doors) operate normally.

What to check

• Read freeze frame and freeze data with a diagnostic scanner; confirm B1404 and any related codes.
• Operate the front left lowering switch while observing behavior and listening at the motor.
• Visual inspection of switch, door harness, connectors and seals for corrosion, pin damage, or water ingress.
• Check fuses and relay(s) for the power windows circuit.
• Backprobe switch connector and measure voltages/continuity while activating the switch.
• Measure continuity between the switch terminals and the BCM (or motor connector) to locate open circuit.

Signal parameters

• Switch supply: approx. 12 V battery voltage present at the switch supply pin with ignition on (varies by vehicle).
• Output signal: when lowering is commanded, expect near battery voltage on the lowering output pin (or ground depending on design).
• Switch closed resistance: near 0–1 ohm between corresponding switch contacts when pressed (manufacturer-specific).
• Open circuit: infinite resistance (OL) between switch output and BCM/motor when the switch is not activated or when circuit is open.
• No communication faults: BCM should be communicating on vehicle bus; check U-codes if present.

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