My check engine light turned into p0171, p0174, p0420 and a p0430?

2011 HONDA ACCORD

112,000 MILES • 3.6L • 6 CYL • 2WD • AUTOMATIC

PERSE.GREY

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So my check engine light has been on for a minute now, it was originally only a p0171, but that turned into p0171, p0174, p0420 and a p0430, i had taken it to a mechanic and he checked the engine for air leaks and he said there wasn't any and then put fuel cleaner in my tank, it was good for not even 2 hours, and then i got the rest of the codes, i don't know what to do

Nov 28, 2025 at 4:33 PM

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JACOBANDNICKOLAS

AUTOMOTIVE REPAIR CONTRIBUTOR
110,190 POSTS

Hi:

The P0171 and P0174 indicate a lean fuel mixture. This can be caused by a few things; however, it is usually an engine vacuum leak. Note that I am basing that on the idea that there are no exhaust leaks before the catalytic converters.

Start by inspecting vacuum hoses, make sure there are no cracks or damage to the air intake tube (between the air filter box and throttle body), and the air intake tube is properly attached at both ends.

Here is a link you may find helpful.

https://www.youtube.com/watch?v=LRKWV4Are5c&t

Next, the two additional codes, P0420 and P0430, are related to the catalytic converters. In this case, both are indicating a problem. The codes mean they are working below threshold.

Before jumping into testing the catalytic converters (it's odd for both to fail at the same time), let's see if we can resolve the lean fuel mixture. If you are unable to locate any vacuum leaks and there is no exhaust leak, we will need to check the fuel pump pressure to make sure it isn't weak.

Let us know what you find or if you have other questions.

Take care,

Joe

Nov 28, 2025 at 6:26 PM