The check engine light had come on, and stayed lit for about 2 days, and then went out by itself, and has not returned so far. The car is 2001 Honda Accord and has high mileage. It has over 100K miles on it.

Even though check engine light went out, I took it to Autozon and got it scanned. It returned P1676 and P0401. Not sure about both, but the 2nd one could indicate the need to replace the EGR valve.... Or since the check light went off by itself, could you it be a faulty sensor?

Can you share your wisdom please?


(I will add, that I had an identical issue with another japanese make car, Toyota, in which the check light stayed lit for few hours and then went out by itself. That has been about 4 or 5 months ago. I did nothing, and Toyota is not giving me any problem)

 

usually when the light goes back off, the problem has gone away. if the computer sees the problem for long enough (or enough instances) it will turn on the light. if it sees that the problem is no longer there after so many drive cycles, it can turn it off. If it comes back, you may have a problem that needs to be fixed. clear out the codes and see if it comes back.

 

A CEL that turns itself off can be due to various reasons. A bad connection to a component can cause this. This can be a one time thing or happen every other time you drive the car.

A problem that is developing which hasn't completely failed but is sitting on the brink of failure so as to cause a CEL to illuminate one day but not the next can happen. P0401 is EGR Low Flow. As your EGR ports get more and more plugged, they will plug to the point that you may have a CEL one day but not the next. Though, the blockage will only increase and the CEL will eventually not turn itself off.

Point being, you might be able to ignore a CEL but eventually you won't have a choice.