Ridgeline NOx Sensor Exhaust Leak

That NOx sensor issue is common, and an exhaust leak can definitely throw things off. The computer uses that sensor to monitor air-fuel ratio, and a leak messes with the readings. Before replacing the sensor, double-check the cable and plug connection for any corrosion or damage. Is the exhaust leak near the sensor? What's the exact error code?

The exhaust leak seems to be coming from near the catalytic converter, so relatively close to the sensor. The error code is P2201. What exactly should I be looking for at the cable and plug? Is there a way to test the sensor itself?

P2201 confirms NOx sensor circuit range/performance. Given the exhaust leak, the sensor is likely getting skewed readings. While you could test the sensor, without proper equipment, it's difficult to get reliable results. Carefully inspect the wiring harness and connector for any breaks or corrosion. The fact you also have an exhaust leak points to the sensor getting damaged. It's probably best to take it to a workshop, they have the right tools to diagnose this efficiently. If it's just the cable or plug connection, the repair shouldn't be too expensive. Parts are about 95€.

Thanks for the advice. I checked the cable and plug again and didn't see anything obvious, so I took it to my mechanic. Turns out it was a faulty connection and the exhaust leak damaged the sensor. They fixed the leak, replaced the connector, and replaced the NOx sensor.