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Engine Code P0171

So I recently changed the air filter in my car. It was a pain in the ass to get to and replace. Its in a tough spot and I am not sure if I secured the cover fully and completely. I am pretty sure I did. Anyway, a week later I had my check engine light come on, it stayed on for a couple hours then went off. It hasn’t come back on since. However, I went to the Autozone, anyway, and had them read the code. They said it was P0171, system too lean bank 1. Is this a serious issue? What are some common ways to fix it, if it is? The car is a 2005, Honda Accord EX. 4 cyclinders. PZEV version. It has 142,000 miles on it. Can someone please let me know what you think? Thanks!

It might have been a momentary issue. If not done already, clear the code and see if it comes up again. If not, don’t worry about it. If it does, check for vacuum leaks, not just vacuum hoses but also devices that use vacuum to work.

If the CEL has not lit up again, then it would appear that everything is okay.
However, there is a fairly obvious possibility as to the cause of the code in the first place.

One of the possible reasons for that code is a problem with the Mass Air Flow Sensor (MAF).
If you accidentally disturbed the connection of the wires leading to the MAF when you worked on the air filter, that would cause that code to show up. Another possible cause is a bad O2 sensor in the exhaust stream, and at 142k miles, a bad O2 sensor is a distinct possibility.

But, if the CEL stays dark, I would not worry about that phantom CEL.

Look at the air intake hose that runs between the air filter housing and the throttle body. If there’s an air leak in the hose after the MAF sensor, the MAF sensor doesn’t measure the extra air entering the engine. The O2 sensor then measures the oxygen content of the exhaust gasses and compares that to what the MAF sensor reading is. So if the MAF sensor doesn’t measure this extra air entering the engine but the O2 sensor see’s a higher oxygen content in the exhaust gasses it will set this code.


Thank you all for the help and comments. I will check this out tomorrow. So the check engine light that popped on and went off is not a serious issue? Just a phantom CEL? So flipping weird.