Q: I have a engine miss codes po174 po420 are on now I had code multiple cylinder miss fire. I changed spark plug wires and plugs l

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I have.a engine miss I have codes po174 and po420 now. I had code first said multiple cylinder miss fire I changed coil unit didn't get better changed plug wires and spark plugs.

My car has 252000 miles.
My car has an automatic transmission.

Hi there. Your issue might be caused by a faulty O2 sensor. You might want to read this article about the P0174 OBD-II trouble code as it will show you possible causes, symptoms and solutions to resolve the problems.

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