P0444, Cel

[ogre73]

'03 Base model, 64K miles. I had the Check Engine Light come on yesterday on my way home from work, so I stopped at AutoZone to have them check it out. Before we even got to the parking lot, he asked if I had gotten gas in the last couple of days. Yes, I said, is there some bad gas out there? He said no, your gas cap probably isn't tight...
I always tighten my cap, but I had to check, of course. It was tight, and he took the code, P0444 and told me the CEL would go away a little down the road. It did go away, but I was just wondering if anyone has ever had this code and found it was anything other than the gas cap? Evidently there is an Evaporative Emission Control System Purge Control Valve Circuit that was Open. Could anyone give me an intelligent answer as to what that circuit is and does?
Thanks.

[bigrod118]

well, that is a common occurance with check engine lights, is that people dont have there cap tight enouhg, and sometimes even going back again and again, so they get a new gas cap.

[blazee]

P0444 isn't a code caused by the gas cap.

Approximately 20%of all hydrocarbon (HC)emissions from the automobile originate from evaporative sources.The Evaporative Emission Control (EVAP)system is designed to store and dispose of fuel vapors normally created in the fuel system;thereby,preventing its escape to the atmosphere.The EVAP system delivers these vapors to the intake manifold to be burned with the normal air/fuel mixture.This fuel charge is added during periods of closed loop operation when the additional enrichment can be managed by the closed loop fuel control system. Improper operation of the EVAP system may cause rich driveability problems,as well as failure of the Two Speed Idle test or Enhanced I/M evaporative pressure or purge test.

The EVAP system is a fully closed system designed to maintain stable fuel tank pressures without allowing fuel vapors to escape to the atmosphere.Fuel vapor is normally created in the fuel tank as a result of evaporation.It is then transferred to the EVAP system charcoal canister when tank vapor pressures become excessive.When operating conditions can tolerate additional enrichment,these stored fuel vapors are purged into the intake manifold and added to the incoming air/fuel mixture.

The circuit you are talking about is the one that the PCM uses to operate the purge valve. During the system test, the PCM opens the valve. When the valve is open the engine applies vacuum to the tank. The PCM then monitors the rate at which the vacuum disipates through a pressure sensor that is in the tank. By doing this it can detect a leak as small as .020". If it senses a leak it will set a DTC. The most common cause is a loose gas cap.

During normal operation, the PCM opens the purge valve to relieve the pressure in the tank.

The code you had was because the PCM sensed a problem with the circuit not a leak.

[ogre73]

blazee,
Thank you. An intelligent, informed answer. Exactly what I was hoping for. Now to figure out why the PCM was seeing a problem with the circuit. This will involve finding the circuit and fully understanding it's operation, then troubleshooting the same. I have to start digging into the Haynes and Google. Again, thank you.

[ogre73]

Update on this thread. About one month after I cleared the P0444 code and decided I would wait to troubleshoot it, I got the P0440 code. Yes, I have been living with the P0440 for that long! I passed inspection by clearing the code RIGHT before taking it down for inspection, but I am tired of trying to trick the inspection station.
Because of the occurance of these two codes in sequence with each other, I am going to be getting another purge control valve and putting it on. Hopefully that will fix the problem. I will keep this thread updated with the progress.
Ogre