Q: Help! P0138 came back after I put engine cleaner in my tank and have replaced the entire exhaust system from headers to muffler.

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Been having a p0138 code setting off the check engine light for a long time so I had the entire exhaust system replaced from the headers to the muffler and it was gone until I added some seafoam engine cleaner. Will it go away after I burn thru the cleaner or am I doomed to have a check engine light haunt me?

My car has 115000 miles.
My car has a manual transmission.

The code P0138 is on for two possible different situations. Either the oxygen sensor has shorted out on the exhaust system or the wiring from the battery to the sensor has a short or break in it. Check the oxygen sensor and see if the wiring is plugged in and if there is any broken wires at or near the sensor. If there is nothing wrong with the harness, then I recommend replacing both oxygen sensors. An exhaust leak can also cause this code to appear, but if you have replaced the exhaust system, then that is ruled out. If you need further assistance with your check engine light being on, then seek out a professional, such as one from Your Mechanic, to help you.

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