2001 Chevy Blazer
We have tried almost everything. We cannot get the 'Cat' or the 'EVAP' monitor to close at all on our OBII hand held. We clear everything then try again. Everything closes except those two monitors. Drive cycles... everything...nothing works. Please Help!

 

The catalyst and EVAP monitors are the most extensive monitors to run and complete. Each step in the drive cycle tests certain things in one or both monitors. If you follow the General Motors Driving Cycle exactly as written, all of the monitors will run and complete their tests. The steps do not need to be done in order, but each step must be completed. With some careful planning, and a little practice, it can be done in about 15 minutes.

 

Ok... now the only problem is... we can't really do the drive cycle here because the roads are not long enough and have too many sharp curves. any other ideas? and also... on the website you gave me on your last message the drive cycle ( can't i just do step 7, since all i need to get closed is the catalyst and evap monitors?)

 

Step #1 checks the oxygen sensors to make sure they are working properly. Each step relies on what was tested in the previous step. Oxygen sensor data is used in steps 2 through 8. At the end of each step in the drive cycle instructions, it tells what is tested during each step. If you see the word "Purge", that is part of the EVAP monitor. If you want all monitors to run and complete, you must do each step, 1 through 8, exactly as written, no exceptions, no variations, exactly as written.

Each step has a different "drive pattern", (different instructions). The PCM is programmed to "watch" for each of the 8 patterns each time the vehicle is driven. When the driver duplicates the pattern, the monitor runs and completes, and the I/M status changes to "complete". If a drive pattern is not completed exactly as written in the drive cycle instructions, the monitor will not complete and the PCM begins "watching" for the pattern again. This is why the EVAP and catalyst monitors can take so long to run and complete during normal driving. I've seen them go for months and remain incomplete. Performing the drive cycle forces all monitors to run and complete in a short period of time.

 

Ok... we completed the drive cycle and it still didn't close those two monitors. Anything we should try next?

 

Yup, do it again. The only reason a monitor does not complete, is because the drive cycle was not duplicated exactly as written.