My check engine light is on with a P0138 high voltage code for bank 1 sensor 2. I replaced the O2 sensor near the manifold (before the catalytic converter) with a Bosch, but the light is still on. Even after resetting the code, it came back. I checked the ground to the engine block, which is good, and the 15A fuses look fine too. Any other ideas on why it’s getting high voltage? Could the rear O2 sensor be causing this and need replacing? Has anyone else had this problem and found a solution?
The P0138 trouble code indicates a problem with the rear O2 sensor on Bank 1 of your vehicle, which is positioned after the catalytic converter. This sensor monitors exhaust gases to ensure that the catalytic converter operates efficiently. The code is triggered when the sensor sends an excessively high voltage for an extended period of time, indicating potential difficulties such as an outdated or malfunctioning sensor, problems with the sensor heating circuit or wiring, excessive battery voltage, corroded wire, or, in rare cases, fuel pressure anomalies. Symptoms include the check engine light going up, decreases in fuel efficiency, and spark plug difficulties.
To diagnose and resolve the issue, use an OBD-II scanner to identify the problem, replace the O2 sensor if necessary with a high-quality replacement, inspect and repair wiring and connections, ensure appropriate sensor function, and ensure all fuses and grounds are intact. Choosing the right replacement sensor might address the problem and restore peak vehicle performance.
I had a similar problem with my car a while back. I got the P0138 code too, and I first replaced the front O2 sensor just like you did, but the light didn’t go away. After a lot of head-scratching, I realized it was actually the rear O2 sensor that needed replacing. The rear one (after the catalytic converter) was sending high-voltage signals and causing the check engine light to come on.
So, I swapped out the rear O2 sensor, and after resetting the code, the light stayed off. Problem solved! I’d suggest giving that a try. Sometimes, even if the front sensor is new, the rear one can still mess things up.
Also, just to be sure, check the wiring and connectors for any damage or loose connections. A tiny crack in the wire can cause weird voltage readings.