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Q: Codes showing: P0171, P0420, P0174

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"We have a minivan and it's showing several codes: P0171 - bank 1-combustion too lean, P0420 - catalyst eff. too low, P0174 - combustion to low What do these things mean. I'm not auto savvy and need to understand before seeing a mechanic."

A: Hello. These diagnostic trouble codes are a...

Hello. These diagnostic trouble codes are an indication that there could be a problem with the oxygen sensor or that there is a vacuum leak. It is possible that the vacuum leak is located in the intake manifold. These codes could also simply be the result of a loose hose. I would suggest that you have a certified technician, like one from YourMechanic, come out and complete an inspection to determine why your check engine light is on.

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