I think I already know the answer is "No" or you would've stated that a relearn can be done by:

1. Disconnecting battery for a few hours.

OR

2. Clearing DTCs with cheap reader.

I ask because I replaced the 02 sensor and cat the day before registration expired. I then cleared the code (and all codes were reset I assume) with a $30 HF code reader. The next morning (cold start) I drove to get emissions checked near work 20 mile trip. The technician stated the vehicle was 'not ready' 4 systems were not 'ready'. I found the GM Drive Cycle and followed it several times. Drove the Blazer about 200 miles and that afternoon took it back and 2 systems still showed not ready: 2nd Air and EVAP.

The next morning (day one expired tags) another cold start (needed to ready 2ndary Air) and following the entire drive cycle several times the 20 miles to the testing site. Still not ready, same two systems.

Drove the Blazer three more days, at least three cold starts and followed drive cycle procedure many, many times. Took car to the technician and the EVAP still showed as "not ready"; however, in Atlanta, one "not ready" is allowed and car past inspection and I paid the late fee to get my tag.

I am assuming "relearn" is not the same as "ready"?

 

Joey1986Z,

Good question! There is a huge misconception about what happens when you disconnect the battery. It will turn off the check engine light however, if there is a "hard fault" present, the light will come on immediately when the ignition is turned on. If there is a fault in a system that is not continuously monitored, such as the systems tested during the drive cycle, the light will only come on after the monitor runs, completes, and the fault is detected. "Short term" memory codes will be deleted, but the "history file" will not. Code readers and entry level scan tools, (commonly used by DIYers) can not access the history file to view it, or clear it. Perfect example of why it was programmed like this: Lets say there's a fault in one of the systems, the check engine light comes on, a DTC is stored in memory, and in the history file. A few days later, the headlights are left on and the battery goes completely dead. The memory file will clear, but the technician can access the history file to see what caused the problem. DTC's in the history file are "temporarily burned" to memory and a voltage loss will not affect them. They can cleared one of two ways: Manually access the file & clear them or, Each DTC is programmed to clear itself after a predetermined number of cycles without a failure.

The reason that you have monitors that are "not ready", is because the drive cycle was not performed exactly as written. The EVAP monitor is, (by far) the most difficult one to satisfy. Different aspects of the EVAP monitor are checked in almost every step of the drive cycle. Under normal driving, it's not uncommon for the EVAP monitor to take days, weeks, or even months to run and complete. The exact driving pattern must be duplicated perfectly for it to complete.

This General Motors Driving Cycle will run and complete all of the monitors, if it is followed exactly as written. With some practice, and careful planning, you can complete it in about 15 minutes. You don't have to do the steps in order, but they must all be done exactly as written for all monitors to run and complete. If you only need a certain monitor to run and complete, you only need to do the steps that include tests for it. At the end of each step, it explains what is tested in each step.

FYI: A "relearn" requires a high end scan tool to command the PCM to perform it.

 

Thanks Captain for your reply. You are very helpful on this site. The Driving Cycle link you provided is the one I used (I might have gotten it from you/this site several months ago). I did, to my knowledge, follow the procedure as best I could. It does look like the secondary air ready check can only be done from a relatively cold start. I wonder if my EVAP is still not ready? I now have a code that needs fixing before the next emissions test. If I resolve it at least a week prior to test date, I'll clear the codes and follow the procedure linked. But, if I wait to the last minute like I usually do, is it better to clear all codes and do the drive cycle thing, or leave the PCM alone and let it clear itself? I am assuming if I do the latter, everything will remain "ready"?

BTW, I lived in Romulus (southeast of DTW - Below Eureka) in the mid 90's. This Southern Boy liked it up there. Bought my 1995 Corvette new at Krug (Now Taylor) Chevrolet off Telegraph. Haven't been there in over 10 years.

00BlazerS10:

Sorry about hijacking your post. I hypermill quite often to increase MPG in all my vehicles. Perform an internet search for hypermill MPG, etc. I'm not extreme like some of the stuff you'll find, but I have gotten good at timing traffic lights on my traveled routes to avoid stopping and letting gravity move the car when I can. I can get mid 20's in my Corvette going over the Appalachian Mountains. Yes, I have to give it gas to get up the mtn, but throw it in neutral (I don't kill the engine, might need the power!) at the peak and let it roll down and hit the curves hard! Fun as well!

 

The steps in the drive cycle must be followed perfectly, if not, the monitor will let you know if you screwed up by not completing

Some of the auto parts stores use scan tools that will access the monitors to see if they are all complete. Might give that a shot before your due date. No worries about hijacking, the questions are all pertinent to better fuel mileage. I'm due South of Willow Run Airport and Romulus is just a stones throw from here. The 4.3's were built at GM Powertrain on Ecorse road in Romulus!

 

We have houses in 3 counties of Georgia. 2 of the 3 are outside of metro Atlanta and do not require emission testing; however, my wife insists to keep her Blazer in Fulton Co. I'm going to push hard to convince her to 'move' the Blazer to one of the other counties and the emission testing will be a mute point. Heck , the Blazer is in Hancock Co. 5 out of 7 days anyway! One good thing about the testing is that at least once a year I fix stuff that I probably would not if the testing was not required.

I remember that big Powertrain plant off Ecorse road. Back then I worked in Plymouth off M14.