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Q: Check Engine Light is on and Autozone read: Trouble Code P0138 O2 Sensor Bank 1 Sensor 2 High Voltage

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I bought this car used about a week and a half ago. The first week it seemed fine with no check engine light but it needed some work. It had the wrong coolant in it, so I had the system flushed and refilled. It was after having this done the check engine light came on the first time. I got a new gas cap and the light went off for a little while, then it came back on and I noticed the air filter was extremely dirty and I changed that. After changing the air filter the light then went off again and I took it for a drive and it performed extremely well; I was surprised at how well it ran and thought I had fixed it. The very next day, though, the check engine light came on again and the car began to run very rough and sluggishly. It has since stayed on and not gone back off. The second time the light came on I also noticed a slight surge of the tachometer. What could this be? Thank you, Jamie.

My car has 135000 miles.
My car has an automatic transmission.

A: Hello. If it has a code for an oxygen senso...

Hello. If it has a code for an oxygen sensor then that may be the issue. The thing about the oxygen sensors though is that they can give a false reading if there is something else going on with the engine.

I usually install a scan tool and see how the sensor is reading as that can tell me if the sensor is failing or if there is another issue with it. If the sensor looks like it is reading improperly then I replace it.

If it seems to be fine then it may be a weak fuel pump, or a misfire issue. It can also be another sensor that is causing it to read like this.

If you are planning on having this rough running condition checked out, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose why it is running rough and why the engine light is on.

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