Almost two years ago I was driving my Accord and as I came to a stop the engine bogged down to a crawl. I took off and it would not go over 10 mph. I got to where I was going and after I got out of the meeting, I started the car and it ran just fine. I then went to the Honda dealer where they said the catalytic Converter was bad and would need to be replaced. They wanted $900. I asked if there was anything else they could do. They ended up resetting the code and said it might last a day or years. Well, almost two years later the codes are back. The engine light is now going on and off from day to day. There is no lack of engine performance and gas mileage is good. The codes are P0420 & P0171. From my research, it could be the upstream O2 sensor or the catalytic converter. Any help in fixing this problem would be appreciated.

 

P0171 is excess lean condition suggesting a large vacuum leak or possibly partially blocked injectors. As ECU tries to compensate by adding fuel trim (Long Term Fuel Trim), converter efficiency might be impacted resulting in P0420 code.

First suggestion would be to look for obvious vacuum leak sources; brake booster, PCV line, etc.

Next would be to clean the Mass Air Flow (MAF) sensor. Dirty sensor can cause P0171 condition.

If these are OK, then fuel injectors may be partially blocked. Diagnosing this is tricky requiring meausure pressure leak down rate w/ a special tool and fuel pressure gauge. You will need a good shop to perform this test.

good luck

 

For the P0171, check the Mass Air Flow (MAF) sensor first. Honda had a service news article regarding to check it first before spending anytime troubleshoot. CRC make a MAF sensor cleaner, available at most auto parts stores, even Walmart should have it.

Leaks at the air intake which can affect the MAF sensor can also trigger the P0171.

 

Update on this problem. I watched a video on Youtube that said to check fuses 4 & 23. 23 was good, 4 was bad. I replaced the fuse and the engine light went out. No codes for now. We will have to see how long it lasts. One question that has passed through my mind. What made the fuse blow?