I found An "L" shaped rubber cap with a sponge inside on my garage floor. Since then my check eng. light has been on. Bought a new gas cap as per Auto Zone Tec. I think the error code is related to th
I think the P0400 error code is related to the "L" shaped rubber cap I found on the garage floor. I can't figure out where it goes. Changing the gas cap had no effect.