P0138 and P0139 O2 Sensor Issues in Nissan Quest (174,000 Miles)
I have a 2015 Nissan Quest with 174,000 miles. I've been consistently receiving diagnostic codes P0138 and P0139, despite having replaced the oxygen sensors already. The issue persists — could it be related to the catalytic converter or wiring? What should I check next?
P0138 and P0139 indicate a circuit-related problem with the oxygen sensor, not necessarily a failed sensor. The presence of these codes doesn't always mean replacement is needed — auto parts stores often recommend part swaps without verifying root causes. I noticed that the previous O2 sensor was replaced with an aftermarket unit from Nissan; however, aftermarket sensors can have compatibility or quality issues. Could you please share your vehicle's year, engine type, and exact mileage? This would help narrow down potential causes.