C1263: Lamp Warning Relay Circuit Open

What does C1263 mean?

C1263 is a diagnostic trouble code indicating "Lamp Warning Relay Circuit Open". This means there is an electrical break in the chassis electronics wiring — a connector may be unplugged, a wire broken, or a component has failed internally. The ECU detected no signal where it expected one.

Symptoms you may notice

• Check engine light (MIL) illuminated on dashboard
• Intermittent warning lights
• Erratic gauge readings

Common causes

• Damaged or corroded wiring harness
• Loose or disconnected electrical connector
• Failed chassis electronics sensor or actuator
• Blown fuse in the related circuit
• Poor ground connection

What should you do?

This code sits in the exterior lighting. Nothing about how the car drives changes, but how easily other road users see you does, and a light out is an on-the-spot fine and an inspection failure. Worth sorting before you next drive at night.