Failed Emissions

[Joe Strahm]

I took my Yukon for the emissions test and during the test the emissions computer picked up a p0440 code which is strange because the check engine light hasn't come in a while. From what Ive heard the p0440 code normally means a bad gas cap but on the emissions papper it says the gas cap passed. But my Yukon failed the MIL CMD. Does anyone know what that means or what it is?

 

[retiredsparky]

During emissions testing, the PCM is asked to turn on and then turn off the "check engine light" or "maintenance indicator lamp" by issuing a command. So MIL CMD failure means the test technician (term used loosely) did not see the lamp illuminate when commanded to.

It could also indicate a loose or open connection in the circuit from the PCM to the lamp.

 

[sumo]

During emissions testing, the PCM is asked to turn on and then turn off the "check engine light" or "maintenance indicator lamp" by issuing a command. So MIL CMD failure means the test technician (term used loosely) did not see the lamp illuminate when commanded to.

It could also indicate a loose or open connection in the circuit from the PCM to the lamp.

I'm a state inspector for RI. We don't manually command the mil on. I can fail a car if I fail to see it illuminate when key is on position. P0440 is. Evap code. When you say not on for awhile, roughly how long ago was that? WhAt it most likely failed for is that the obd monitors are not ready.
These components are automatically looked by the inspection machine. You can have all but 1 monitor not ready and it's the evap that's last to be teafu

 

[retiredsparky]

Good comment, Ian. Thank you for clarifying about the MIL command.

The evap code can be the purge valve starting to not seat correctly. It is found under the hood connected to the intake manifold. If you drive on dusty roads, dust gets sucked into the evap system whenever the purge valve is commanded to open. Then, when it tries to close, it can't. Also the charcoal cannister gets dust in it and the vent solenoid also gets dust in it. Watch the video below for a good illustration about how to replace the components. You can clean some of the parts up, solenoids cannot be easily cleaned out.

 

[sumo]

Haha I knew I must of had a incomplete post out there. I remember starting and don't remember finishing. Zzzzzzzz