Check engine light keeps coming back on after work is done

The most common mistake is thinking diagnostic fault codes say to replace a part or that one is bad. In fact, they never do. Fault codes only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. Many people replace oxygen sensors when they report a bad condition, but in reality, the sensor has to be good and working properly to detect and report that bad condition. Changing a sensor won't fix what is causing the problem.

The first concern here is we need to know the exact fault code number. Your Engine Computer can detect well over 2,000 defects. There can be over a dozen fault codes pertaining to just one of the oxygen sensors, and they mean very different things. Once we know the code number(s), we can figure out how to proceed.

Please list the engine size too. We use that information when diagnosing engine-related problems and suggesting the most common suspects.

Dandy. The "OBD2" just means the car has "on-board diagnostics, version 2" emissions system. All cars and light trucks sold in the U.S. starting with 1996 models have that.

Here's a list of the generic fault code numbers we use for reference:

https://www.2carpros.com/trouble_codes/obd2/p0100

Not all are used by every manufacturer on every car model. There's also a lot of manufacturer-specific codes over 2,000 now too. When you're told the fault code number, it may start with a "P", such as P0442. That is for a power train code, meaning it's stored in the Engine Computer.