B1406 — Front left electric window lowering switch short to ground

Causes

• Damaged wiring harness (chafing, pinched, or exposed conductor) to front left window switch
• Faulty front left window switch with internal short to ground
• Corroded or contaminated connector causing unintended ground
• Poor or loose ground at connector or BCM pin
• Short inside door harness or to chassis ground after recent repair or door removal
• Faulty BCM (rare) or internal circuit failure

Symptoms

• Front left window will not lower or operate correctly
• Window operation intermittent or only works in one direction
• Other windows or door functions may be unaffected (localized to front left)
• DTC B1406 stored and may light console warning/message (depending on model)
• Blown fuse in rare cases if short draws high current

What to check

• Visual inspection of front left door wiring, switch and connectors for damage, corrosion or pinching
• Check relevant fuses and relays for the power window circuit
• Use scan tool to confirm B1406 is current or stored and clear then retest
• Measure switch connector voltages with ignition ON (verify pull-up voltage and ground reference)
• Check continuity/resistance between switch signal pin and chassis ground with switch disconnected
• Wiggle test wiring through full door open/close range to reproduce fault

Signal parameters

• With ignition ON and switch disconnected: switch signal pin typically pulled HIGH (~8–12 V) via BCM or internal pull-up
• When switch is pressed to lower: expected transition to ground (0 V) if designed as active-low — but not an permanent shortToGround condition
• Short-to-ground condition: persistent ~0 V on switch input when switch not operated
• Open circuit/very high resistance indicates broken wire (>10 kΩ)
• Short to power would show ~12 V on signal pin when circuit should be low

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