Standard Ignition EFL166 Ambient Light Sensor

Ambient Light Sensor for GM Vehicles

Standard Ignition EFL166 is an ambient light sensor used to monitor exterior light levels and send the proper signal to the vehicle’s lighting control system. It is a direct-fit electrical replacement for a range of GM cars, trucks, and SUVs, including Chevrolet Silverado, GMC Sierra, and Pontiac Grand Prix applications.

• Ambient light sensor for automatic lighting control systems
• Black housing with clip attachment method
• Female 10-pin rectangular plug-in connector
• 2 blade terminals with male terminal design
• Direct replacement for select GM vehicles

Fitment and Application Details

Compatible With 1999-2004 Chevrolet Silverado 1500, 1999-2004 GMC Sierra 1500, and 2000-2005 Chevrolet Impala applications that use an ambient light sensor in the lighting control circuit. Standard Ignition EFL166 also fits 2005-2007 GMC Envoy, 2005-2007 Pontiac Grand Prix, and 2004-2005 Saturn Vue models, along with additional Buick, Cadillac, Chevrolet, GMC, Oldsmobile, and Pontiac vehicles listed in the fitment data.

This part cross-references AHS100 and SU8209 for the same application. The EFL166 part number is also searched by buyers looking for an ambient light sensor for Chevrolet Silverado, GMC Sierra, and Pontiac Grand Prix repair work.

What This Sensor Helps Address

• Automatic headlights that do not respond correctly to changing light conditions
• Lighting systems that stay on or switch at the wrong time
• Fault codes related to ambient light input or sensor signal loss
• Intermittent exterior light behavior caused by a failing sensor
• Restoring proper operation in vehicles with factory light-sensing systems

Installation Notes and Tips

Verify connector style, terminal layout, and mounting location before installation. This sensor uses a clip attachment method and a plug-in rectangular connector, so the existing harness and mounting point should match the original unit. Confirm the vehicle’s lighting control diagnosis before replacement to avoid unnecessary parts changes.

Quality Assurance

Standard Ignition supplies replacement electrical components for service applications, and EFL166 is built to match the listed connector and terminal configuration for the specified vehicles. Review the fitment list carefully for your exact year, make, and model before ordering.