O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)

Bank 1 downstream O2 sensor reading high voltage (stuck rich above 0.9V). This often indicates the catalytic converter is failing and allowing rich exhaust to pass through. Check for P0420 as well. If the cat is not failed, the O2 sensor itself may have an internal short. Replace with an OE-quality Motorcraft unit. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.

Bank 1 Sensor 2 stuck high voltage. Check for a rich-running condition first by monitoring fuel trims. If the upstream sensor shows rich, fix that issue first. If fuel trims are normal, the downstream sensor has an internal fault. Replace with an OE-quality ACDelco unit. Also check for antifreeze contamination of the cat from a leaking intake manifold gasket. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.

Downstream O2 sensor stuck high. If the voltage stays above 0.8V constantly, the sensor is either shorted or the cat is passing rich exhaust. Monitor the upstream sensor for a persistent rich condition first. Replace the downstream sensor with Denso if it is confirmed faulty. Use penetrating oil before removal. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.