Around here if the CEL is on you fail before they even hook the computer up for testing. I would try the anti-fouler trick previously mentioned. If you disconnect the battery to clear the code make sure you run the car through a complete drive cycle prior to testing. All the monitors have to run their tests and be flagged as 'ready' or you will fail again. I would conduct the drive cycle a couple of days before testing then drive the car a few times under various conditions just to be sure all monitors are set as ready.

General Motors Driving Cycle < Link

 

Yep you have to have the CEL tuned out - I had the 2.5 ZZP downpipe w/high flow cat on my 05 SS - bought their canned PCM tune and they tuned the code out and I passed.

 

I had the downstream O2 fail on me, along with my ABS messing up, so I tried to reset the codes first, since the lights would stay off as long as the car stayed on (never had a problem before), and then they'd just tailpipe test me. New policy is they have to turn the car off and back to ACC to make sure the light works, then start the car and scan for codes.

 

No emissions in Iowa either some days I think I hat this ole hick state but other days I wouldnt trade the whole state for a mansion in Cali.

 

I helped a friend get a '00 Cavalier to pass eCheck (I won't say how but I can say a Snap-On scan tool was involved and it got tail pipe tested since it was no longer in it's "ready" state). Best part, it passed with GREAT numbers as the service person said.

My '94 Grand Am passes ALL the time (but they never scan it since it's too old). It has an ABS light now but and for about 8 years it's had a pesky code 77 (EGR solenoid #3) code. I've done everything I can find to try and resolve that code (last one was replace the EGR). No change. I decided since the car seems to suffer NO performance/fuel economy issues and it passes eCheck (and the numbers it passes with are really good each time) with it, I gave up trying to fix it. Heck the LAST TIME the girl that pulled the slip told me she was surprised how good the numbers were considering it's age!

 

Yep, that's the way they do it around here also. If the CEL doesn't illuminate and complete the self test the vehicle fails before they even plug the computer into the OBDII port.

We don't have the option of a tail pipe sniff. That test is only performed on '95 and prior vehicles. '96 and newer they check for monitor readiness flags. If any of the monitors have not completed their test (performed every time the vehicle is started) and in the ready state the vehicle fails.

 

The check engine light itself is not seen , I have a PEICE of tape on the inside of it so it can't be seen.mthe light would never ever go out,MIT bugged me so much,mi taped the inside. The emmission place never seen the light. He was puzzled why the light wasn't on. Wish I'd have never changed the cat with a high flow, never again!

 

Hello, how much was it? I can't find it at zzp... Thanks.. Mjc.. I'll just try this first.. Any info,mgreat...my.. Mjclemm...

 

Lol.. Oh I understand, my wife took it in without me even knowing about it.. She thought she was doing me a favor and not bothering me with it..lol.. Well that just worked out great! See, the cel bugged me so much because of the Zzp pipe. So , when I had the dash apart, I put black electrical tape on the inside of the light cavity so it would not illuminate the cel. Works great, if you don't have your wife sneak the car in !lol... Now, I need to get it corrected,nth is sucks... Oh well.. I guess the black cloud over my head should have been a heads up...

 

Are you sure the cat was the cause of the vehicle failing? Technically, the attendant should have failed the car for the CEL not illuminating:

Wisconsin Vehicle Inspection Program

No matter what, you're going to have to eliminate the PO420 code, make the CEL visable for testing and do a drive cycle to get (all but 1) monitors in the ready state in order to pass the test.