2004 Civic CEL MAP Sensor



My 04 Civic with 85K miles, has had a persistent issue with the CEL indicating an error code of P0171 (MAP Sensor) implying too lean of a fuel mixture. Honda has replaced both primary and secondary o2 fuel sensors, the EGR valve, the fuel injectors to no avail. The CEL returns within a day or 2 after each “fix”. Honda is now stating the problem is due to the ethanol mix in gasoline. I cannot buy gas in my state (NC) that is ethanol free. I have seen some posts on other boards that suggested either a cracked manifold, bad catalytic converter, or failing fuel pump. Honda states if these were the cause, they would see a different error code. HELP! Anyone experience anything like this?


P0171 is the code for a lean mix on bank 1, but hwre does the MAP sensor comment come from? Did you also have a P0100, 101, 102, 103, 104 or something in that range?

Your dealer is throwing parts at the problem hoping it will go away. Try a reputable independently owned and operated shop. The signals from these sensors can be read to verify whether they’re working properly or not before changing them.

I can guarantee it is not the ethanol in the gas. I can also say with certainty that it is not the cat converter. That has no effect on the fuel metering. It could be a vacuum leak such as a cracked manifold or another vacuum leak source, but vacuum leaks can be definitively diagnosed. I also doubt of it’s a failing fuel pump, but as with the other things that can be definitively checked.

I’m wondering where the MAP comment came from.

It sounds to me like your biggest problem isn’t the car…it’s the lazy bums at the dealership.


One reason that a P0171 might be thrown is a dirty or faulty Mass Airflow Sensor (MAF). So I wonder if you didn’t mean the MAF sensor rather than the MAP.

Either way, to put it bluntly, the people who have been working on your car are either incompetent or just don’t care (or both).

Has anyone cleaned the MAF? Checked its operation? Has - as mtnbike noted - anyone checked for vacuum leaks?

Fuel delivery problems could also play - has anyone checked the fuel pressure?