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coachk_23
New User
May 15, 2008, 7:53 PM
Post #1 of 3
(19924 views)
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DTC PO440
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1999 PONTIAC GRAND AM SE
3.4 LITER V6 ENGINE
105,000 MILES
SERVICE ENGINE LIGHT CAME ON WHILE DRIVING DOWN THE ROAD. NO NOISES, NO PERFORMANCE ISSUES. HOOKED UP OBD-2 AND FOUND CODE PO440, CLEARED CODE. REPLACED FUEL CAP WITH NEW ONE. CODE HAS RETURNED. NOT SURE HOW TO DIAGNOSE FURTHER. HOW MANY EVAP SENSORS ARE THERE ON THE PONTIAC GRAND AMS AND WHERE ARE THEY LOCATED? THANKS FOR THE HELP.
coachk_23
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DanD
Veteran
/ Moderator
May 16, 2008, 8:55 AM
Post #2 of 3
(19910 views)
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A P0440 Large EVAP leak sets when the PCM does an EVAP integrity test on the system and it fails.
Large leak is a relative term in this case, anything that will allow pressure to escape from a .020” hole, is considered a large leak.
Any time the fuel level in the tank is from ¼ to ¾ full is when the PCM may run a test.
The PCM will turn on the purge solenoid; which will allow engine vacuum to enter the system.
The PCM will also turn on the vent solenoid sealing the vent.
The PCM will now watch the EVAP pressure sensor, which should be showing an increase in negative pressure in the EVAP system.
Once a certain pressure is reached (depending on fuel level); the PCM will turn off the purge solenoid; completely sealing the EVAP system.
Now the PCM will watch the pressure sensor; timing how long it takes for the pressure to leak down.
So if the pressure cannot be reached or if the pressure degrades too quickly; on comes the light and the 440 sets.
Causes could be the purge solenoid, vent solenoid, pressure sensor, vacuum supply to the purge solenoid, wiring, PCM or a leak anywhere in the system, larger then .020” (pin hole).
The purge solenoid is under the hood, the vent solenoid under the car close to the fuel tank and the EVAP pressure sensor is on top of the fuel tank.
The testing is quite simple with the proper equipment; a scan tool to command the solenoids on & off; an EVAP leak test/smoke machine, to apply smoke to the system under low regulated pressure.
The smoke is there as a visual aid, you won’t see gas fumes leaking out of that small of a hole or leak in a line or solenoid.
You asked and I hope you understand; it’s not just having the knowledge of how the system is designed to work but also having the equipment to run the tests.
Dan.
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Canadian "EH"
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coachk_23
New User
May 19, 2008, 1:34 PM
Post #3 of 3
(19891 views)
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Re: DTC PO440
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THANKS FOR THE EXPLANATION. IT HELPS.
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