97 Bravada reset OBD II codes

[greggreg]

I'm trying to get through my emissions test. Had to replace the O2 sensor and reset the OBD codes. I've driven it for a couple days and have all IM codes 'ready' except EVAP and HO2S. I can't seem to get these to get "ready". I have no OBD codes right now but need to get these last two codes 'ready' before I can pass the test. Any way to drive/run my truck to get these two codes to reset? Note: I've done my best to do the 'drive cycle' but would like to know what specific drive or runs I need to do to get these two codes ready. Thanks!

[Chris Stewart]

You might try going to a chain type autoparts store and get a free scan then reset the trouble code.

I miss my '97.

[greggreg]

Thanks Chris. I have my own reader ($50 at Harbor Freight). I reset the codes myself. I have no outstanding codes but I need to get all IM items 'ready' or they won't pass my emissions test. (they use the onboard diagnostics for the Missouri emissions test for cars/trucks later than 95) The issue is getting that EVAP and HO2S code 'ready'. My reader will tell me when they are, I just need to drive/run the right way to get the OBD computer to register them as 'ready'. Anybody got any ideas?

[old_master]

Here is a link to the GM drive cycle procedure. This MUST be followed EXACTLY or all monitors will not run and IM readiness will not be complete.

http://www.obdii.com/drivecycle.html

[ericn1300]

try this: http://lyberty.com/car/drive-cycle.html

[greggreg]

Ahh, good. Let's talk about this GM Drive Cycle. Short of having your own personal test track, how can any normal person ever do the GM Drive Cycle "exactly"? First of all you need to cold start and run for 2.5 minutes and then accelerate to 55 for 3 minutes. Now, unless I have my truck sitting COLD (i.e. overnight) on the side of the highway (not likely!!), how can I do this? Then I need to drive for 3 minutes at 55 and then coast to 20 without touching my brakes. So at "exactly" 3 minutes down the road I need a very long exit ramp - Not likely! (Note: if I try to just coast down to 20 while still on the highway I'm going to get killed!) Let's get real!!! "Normal" driving should reset all codes eventually. I could drive 10 years and not "coast from 55 to 20 without using my brakes"!!! So, since I haven't done the Drive Cycyle exactly, I will NEVER reset my codes??? This doesn't make sense. While the "exact" drive cycle may reset the code, there has to be some other criteria which will also reset the codes, otherwise "normal" driving would not reset the codes! Any thoughts?

[old_master]

The IM readiness is not a “reset” by any means. All monitors are reset when the DTC’s, (Diagnostic Trouble Codes), are reset. The IM readiness mode of the scan tool tells you which monitors have run and completed their tests since the last time the DTC’s were cleared and the system was reset. Each monitor must run and complete its tests before a DTC can be set. For example: if there is a problem in the EVAP system, the SES, (Service Engine Soon) light will not illuminate until the EVAP system monitor runs, completes its tests, and detects the problem. That’s why they won’t pass/fail your vehicle until all of the monitors have run and completed their tests.

The drive cycle in the above post is the quickest way to force all of the monitors to run, and complete their tests. Each monitor uses a different set of circumstances in order for the monitor to run and complete its test. Some tests only run once per drive cycle. Some only run once per drive trip. Others continuously “watch” for the conditions to be met. If any test is not completed during the drive trip or cycle, the PCM/VCM waits for the next drive trip, or drive cycle, and attempts to run the test again. It will continue to attempt the test until it runs and completes. Under normal driving conditions, all monitors will eventually run. If a certain monitor takes longer to run and complete, it’s because the driver has not produced the exact conditions necessary to run and complete the test. If you have a monitor that is incomplete, the drive cycle instructions will tell you what you need to do to get it to run and complete. You can pick and choose which monitor you want to run by doing what the instructions tell you for each particular monitor, you don’t have to do the whole thing. Hope this helps.