Code P0455; '99 Escort

Car has about 75K miles. Son has the car out of town (again), at school. He reported CEL (SES?) light on; “what should I do?” Told him to have it checked. He has trusted mechanic nearby, so I told him to go there. They say they don’t just read codes (“You can get Autozone to do that”); they do diagnosis. Good!

Report: Code P0455 (gross evap leak). Did smoke test; nothing. “Did you maybe have it running when you filled gas tank?” (No.) They reset the CEL, and sent him on his way.

Should we be satisfied if CEL stays off? What else to try or to look for if same code comes back?

Had he recently gotten gas? If the gas cap is not closed properly, the engine computer will detect a leak in the evaporative emissions system (seals the gas tank to keep gas fumes from polluting the atmosphere) and set the check engine light. If you simply re-seat the cap properly, the light will go out by itself when the computer fails to detect a consistent fault after 4-5 engine start/stop cycles. This is probably described in the owner’s manual, and would be the first thing to check when the CEL comes on.

If that was the problem, then you are done. If the CEL comes back on, then you have some other kind of problem, either a leak in the evap system, or a faulty gas cap, or a problem with the computer falsely detecting a leak. It’s not an urgent driving hazard, but the car probably won’t pass inspection next year until it’s fixed.

SDWH – thanks. I forgot to mention that the gas cap was properly in place, and that he had already gleaned that info from the manual (what a guy!).

If it comes back on right after filling the gas tank, then ask him if he added gas after the first click of the pump handle. If he doesn’t stop on the first click, he can temporarily clog up the evaporative emissions system. Eventually this practice will do permanent damage.

First, this kind of code isn’t going to result in any disaster for the car. Chances are the driver won’t even notice anything. So clearing it and waiting to see is the best place to start.

That said, if the code returns, I’m fairly wary of a shop that does a smoke test on a “gross” leak and can’t find it. Find out exactly what was smoke tested. If he wants to check the “easy” parts its not that hard - it mostly involves pulling the battery & battery tray and the air filter housing. This is not complicated. The main feed for the evap runs behind the intake manifold, down under the battery, then under the air filter housing, and then to the charcoal canister which is more or less in front of the driver’s side fender well. Another line feeds from the canister to the purge solenoid & valve & then to the bottom of the throttle body. Actually you can eyeball the throttle body feed without removing anything.

When it comes to the rest of the line (under the car & back to the tank), you probably want a mechanic & a lift.

Keith – Thanks. He knows not to “top off”.

Cigroller – Thanks for that info. I do (some time) want to learn more about smoke tests – how they are done and what they test. [See note below.] Son is busy in school now, and, if problem stays gone, he does not have time to investigate or to query the mechanic. (If I could swap cars with him, I’d have myself a fun project! I should probably start reading my Haynes manual.)

I don’t know how much the car has been used since he got it back, and he’ll be away for a couple of days. I’ll post back if there is any interesting follow-up info.

Note: I know what we meant by “smoke test” in electronics and ham radio. And in explosives and pyrotechnics they use the “Time to Fume” test. But I’m sure this is something different. :>)