PO440 DTC code reset success [Archive] - GrandAmGT.com Forum


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09-17-2004, 04:05 PM
Just wanted to say thanks to those folks in this forum who posted their experiences
with evaporative emission control failures and MIL reset. At 79,000 miles my Grand Am has been trouble free until a required emission test resulted in an OBDII dtc
failure code. PO440 - Evaporative Emission Control System Malfunction.

The Washington state emission facility stated that the gas cap was fine but, after
reading posts here and in alt.autos.pontiacs I decided to buy a $10 dollar replacement cap. Disconnected the battery for 3 hours after replacing the cap and have had no MIL since. Passed the retest with no problem.

Thanks again!

solfoo lol

09-18-2004, 07:53 PM
Just a question. Has your SES light came back on? The reason I ask is that OBDII WILL NOT clear the codes merely by disconnecting the battery. The light stays off because when the battery is disconnected, the OBDII system goes back into a learning mode. At that time, it is receiving information from all the sensors and calibrating themselves according to what information is stored in the PCM.

It was because of that relearning mode that I passed my emissions test. Here in my section of Ohio, 96+ cars do not need a tailpipe test, either done at idle or on a dyno. A true scan tool is plugged into the OBDII port. From the readings it pulls, your car is determined to pass or fail. However, if your SES light is lit for any reason, you will fail the test regardless of the DTC. If you get some DTC due to, say, faulty torque converter lockup...you still fail. I am throwing a P0500, Vehicle Speed Sensor inoperative. I disabled my governor by cutting a wire to the PCM so I could exceed the 106mph max speed! :P Well, VSS inoperative IS NOT EMISSIONS RELATED, but I would have failed. However, I know my car will pass a dyno test...with flying colors.

So, I left the battery disconnected while at work. When it came time to leave, I reconnected it and drove 10-15 miles to the testing station. When they hooked up the OBDII scan tool, it said "unable to communicate with vehicle ECM" or something to that effect. The tech said I could come back later and get the OBDII test or have the car put on the rollers. Seeing as to how I will pass on the rollers, I opted for that. While waiting for my printout from another tech, a service mgr from a local dealership was in having a used car tested prior to sale. He explained to my that the OBDII system needs to go at least 40-50 miles before it has learned everything and thus communicate with a scan tool.

So it may seem that I cheated the system and in some aspects, I did. However, by using actual tailpipe tests which quantitatively measure the actual exhaust gases rather than using stored data, I still passed with flying colors. In fact, I ran cleaner now than I did in 2002, my last test year. I was damned if I was going to let a SES light for a problem unrelated to emissions fail me.