Readiness Monitors / Drive Cycles

JP02Silverado · January 26, 2010

My '02 Silverado has a code PO446 caused by a malfunctioning vent solenoid. I'm aware that this is a common problem in these trucks and GM has created a kit to re-route the vent to a different location using 5/8 heater hose and clamps. (while charging a nice premium for those parts to fix their screw-up) I have gotten two estimates (one from a local dealer) of a minimum of $500. NO WAY am I paying that much just to turn off a light on the dash. I'll do it myself, but have been putting it off because I've read everyone elses' stories and I dread having to drop the tank.

Its inspection time and I don't think I can get it done before I'm overdue. My state allows one readiness indicator to show "incomplete". I'm trying to get all the other indicators to show "ok" except for the evap. It happened one time 2 weeks ago when I was out of town (Murphy's law). Now I can't get the catalyst monitor to become ready before the evap monitor. I have done several drive cycles and cleared the codes 4 times.

My question is: which part of the drive cycle tests the catalyst monitors? How can I get it to clear before the evap?

I can't express how much I HATE such government intrusion into our lives. What are the chances all these fancy sensors will outlast the rings and pistons? I've already spent $700 replacing the instrument cluster and knock sensor. Just a few more problems like this and I'll find a permanent solution to the whole OBD system.

rmck490 · January 27, 2010

My '02 Silverado has a code PO446 caused by a malfunctioning vent solenoid. I'm aware that this is a common problem in these trucks and GM has created a kit to re-route the vent to a different location using 5/8 heater hose and clamps. (while charging a nice premium for those parts to fix their screw-up) I have gotten two estimates (one from a local dealer) of a minimum of $500. NO WAY am I paying that much just to turn off a light on the dash. I'll do it myself, but have been putting it off because I've read everyone elses' stories and I dread having to drop the tank.

Its inspection time and I don't think I can get it done before I'm overdue. My state allows one readiness indicator to show "incomplete". I'm trying to get all the other indicators to show "ok" except for the evap. It happened one time 2 weeks ago when I was out of town (Murphy's law). Now I can't get the catalyst monitor to become ready before the evap monitor. I have done several drive cycles and cleared the codes 4 times.

My question is: which part of the drive cycle tests the catalyst monitors? How can I get it to clear before the evap?

I can't express how much I HATE such government intrusion into our lives. What are the chances all these fancy sensors will outlast the rings and pistons? I've already spent $700 replacing the instrument cluster and knock sensor. Just a few more problems like this and I'll find a permanent solution to the whole OBD system.

Google "Drive Cycles". You'll find a lot of choices for GM vehicles. Most vehicles are the same but there are differences. You'll need to complete both a highway speed and in-town speed. I suggest doing it late at night when traffic is minimal because you will need to coast from a highway speed to nearly nill without touching the brake pedal.

My 2000 Silverado had this P0446 code once. After reading all the internet stuff and the TSB on this, I chose to fix it myself. I simply pulled the EVAP vent valve and blew the dust out of it. No problem since doing that. Caution, however, there's a spring, a pintel and a rubber disc that can seperate when you do this. If they become seperated, you'll have to fix this before re-installing the vent valve. It took me about two hours to do the job and I didn't relocate the valve like the TSB kit instructions call for. I don't live in a dusty environment so I didn't see the need to move it.

minibike132 · January 27, 2010

STOP CLEARING THE CODES!!!!!!!!

Stop clearing the codes, stop clearing the codes, stop clearing the codes.

The code tests need to run and pass, not run and pass on the previous run cycle. If a code passed the last test it will pass I/M readiness. Every time you clear the codes the readiness resets and reads "not run" or "not passed" since previous clear. The reason for this is so that you can't clear the codes in the test lane and have the vehicle pass because there are none set.

It can take tons of drive cycles to get all the readiness monitors to run and pass or fail. Stop clearing them, drive it as you normally would, and take it up when they have all run and passed.

I could spend hours compiling all of the things that need to happen for each individual code to run and it would still be impossible to predict when they are going to actually run. For example if the code says it needs XXXF coolant temp and XXF intake air temp and ZZZ drive time and XXX miles per hour for 2 minutes you could make sure the vehicle was run under those conditions and you may not get the code to run. Just because the vehicle needs those particular conditions met to run the diagnostic doesn't mean it actually will run it.

Just drive it and watch the monitors and you should be good to go in no more then a few weeks.

JP02Silverado · January 27, 2010

Stop clearing them, drive it as you normally would, and take it up when they have all run and passed.

But they won't all pass, and I already know which one won't pass. I don't have time to deal with it right now and I need an inspection very soon. I want all the readiness monitors to set to "okay" except for the evap. (my state allows one incomplete) If I can get it passed I'll have another 12 months to fix it. My problem is that the evap monitor turns on the CEL before the catalyst monitor is ready. I need the catalyst monitor set to "okay" before the evap ...which has only happened once when I couldn't get to an inspection station.

Is there some kind of software available that will allow you to set individual monitors to the "ready" state without doing a drive cycle?

frankstl · March 2, 2011

Yea this readiness and drive cycle crap is for the birds, I mean its either blowing acceptable level of emissions or its not, im having the same issue with my truck, 99 4x4 with a 5.3 and its showing not ready on three of them, sad thing is my mechanic whom I only have do major repair work as I do everything else myself, told me to try and give my truck a tune up and if lucky that would fix my codes 171 and 174 which he said was a lean condition on the left and right banks, so I go by plugs and air filter, drive the truck for about 15 or 20 minutes and the light goes off, and this thing had been on for about a year and a half now, well anyhow still was off after about 100-150 miles of driving and I took it to the mechanic to check again for me and he cleared the previously stored codes and screwed me I guess because now 5 days and about 600 or 700 miles later three monitors(evaporative, heated o2, and catalyst)still have not reset. And our state will allow 2 of them not to be reset, all that being said, the drive cycle is rediculous as well, I mean comon it states I need to turn on my ac to full along with rear defroster lol wtf? Anyhow then start the vehicle and let it idle in this condition for 2.5 minutes, then somehow magically jump from my driveway after that to the highway with half pedal pressure till it hits 55 and do that for 3 minutes, then let it coast down from 55 to 20 whilst in gear, if level ground maybe in half a mile lol, then apply 3/4 pedal pressure till it gets to 55-60 and maintain that pressure for 5 minutes, and walla they should reset, what a joke.

I have done this 3 times and its a crock, the manufacturer knows of this major hiccup, so do the legislators, thats why 3 years ago roughly they made it a law that people have 30 days to get the vehicle to readiness if it fails the first test, well now I am having to be hassled anyway and pulled over and re-explaining my trucks issues and etc, made late for work or wherever im supposed to be as a result of this, and etc. etc. etc. So now 6 days later still no check engine light and 4th test still same 3 monitors not ready, im not an ase mechanic by any means, but the info on drive cycles is not in the owners manual, but thats where it should be, also there should be no drive cycle, either the sensors work within limit or they dont, if not replace it when out of range/limit. My truck has 170k miles and I can run it 5 and 6k between oil changes sometimes and it doesnt even use a quart of oil, my wifes car on the other hand an 07 with the same 5.3L with only 70k and fuel management on it and it cant even go 1500 between oil changes without tripping the engine oil low add oil warning light at which point we add between 1.5-2 quarts of oil to get to full mark again, and by the time the 3k mark gets there for the next oil change its low again, thats a load of crap and dealer is telling me thats not unusual with these newer cars. What a load that is, they even took the heads and intake off and said there was a known issue for oil consumption on these cars and had something to do with the lifters and pushrods, but immediately after we got the car back the same thing was still happening, and if you ask me they dont want to replace the rings/engine to fix it and are trying to pass the buck till we hit the 100k mark.

Anyway good luck with your problem and if you find out any relevant info please pass it along and I will do the same as I am looking and looking and will not stop except while working and sleeping till I find the fix/solution.