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S-M-O-G! Oh Boy, Here We Go Again!

P0440 OBD-II Trouble Code-Evaporative Emission Control Sys
Posted March 23 2007 11:30 AM by 5569 
Filed under: Bloody Knuckles


My truck has a bad habit, called an illuminated "Service Engine Soon" light.

 This is perpetual; when it's not on (because the battery was recently disconnected), my dash looks unfamiliar to me. I am obliged to tackle this whole "check engine" light situation (thus putting other fun modification on hold), in order to get the darn truck smogged, in order to renew the registration. (S-m-o-g, it's the OTHER four letter word.)

This is my smog journey, and you're coming along with me!

The most recent code is P0440, Evaporative Emission Control System Malfunction. Don't we all love the vague codes? My first thought, and it made perfect sense, was to put the stock gas cap back on the truck, since I had an aftermarket locking cap, which wasn't sealing properly. (And an aftermarket gas cap can fail your smog visual.) After clearing the code, it predictably reappeared about 80 miles later. Silly me for actually thinking it would be that simple!! So, still being convinced this was the most likely reason for throwing the P0440 code, we lubed the stock cap's seal, since it had been off the truck for some time. Forty miles later, the light has not come on again, but I'm thinking that it will by tomorrow morning. 

I do not know what the problem is, but I will keep you up to date, just in case you run across the same thing sometime. Or, perhaps you HAVE had this problem and you can tell me what it turned out to be!

The disconcerting thing is that the truck SHOULD be stock, in terms of the EVAP system and emissions. However, I can't say that every part of the Evaporative System has never been touched at all, with all of the relocating that's been done. That means that we could be in for quite a journey - a journey I'd rather not have to deal with.


Technical Description
Evaporative Emission Control System Malfunction
What does that mean?
This indicates that a part of the EVAP control system is no longer functioning correctly. The EVAP system consists of many parts, including (but not limited to) the gas cap, fuel lines, carbon canister, purge valve, and other hoses. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

You likely won't notice any drivability problems.

A code P0440 could mean one or more of the following has happened:
* The gas cap is not installed or working properly
* The purge solenoid has failed
* The canister is plugged and not working properly

Possible Solutions
With a P0440 OBD-II trouble code, diagnosis can be tricky at times. Here are some things to try:
* Remove and reinstall the gas cap, clear the code, and drive for a day and see if the codes come back.
* Inspect the EVAP system for cuts/holes in tubes/hoses
* Inspect for damaged or disconnected hoses around the Evap purge solenoid
* Check and/or replace the sensor
* Check and/or replace the purge valve
* Have a professional use a smoke machine to detect leaks

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