Well, I learned something new today:  Drive Cycles …. 

A couple days ago my 1997 BMW 540i failed an emissions test (for the second year in a row).  Last year I had shown enough money spent on the engine to get a waiver.  This year, I was a little nervous because I didn't know whether they'd give me a second waiver or not.  (This vehicle is a blast to drive and a PIA to take care of or work on!!)

Well, I just got done speaking with the head of the Air Quality Testing for ADA County, my new friend Roger (I have to say that it's nice to be able to talk to the head of the department — that's one nice thing about living in a small populated state).  What happened was not that I failed, but that they couldn't read my car's computer.  The reason was that I have not completed a drive cycle since the last time I reset my car's computer codes (Any time I work on it, I reset the codes to see if I have fixed the problem).  I figured anytime I got into the car and drove it that the computer would be on and recording normally.  However, until a drive cycle is complete, none of my monitors (which are really groups of codes) are actually capable of being read.  So, Roger, who said he consulted with the EPA back in 1992, said he had a good deal of insight into what constituted a drive cycle.

PREP:  First he said, I had to have between 1/4 of a tank and 3/4 of a tank of gas.  Otherwise, the drive cycle is cancelled.   Also, drive the car until it's warm, then park it, turn off all high load accessories, including in the BMW's case the radio and A/C unit.  Let cool.

BEGIN CYCLE – IDLE:  Leaving all accessories off, turn on and idle the car for two minutes.  This will create an idle stablization. (at this point he launched into the horrors of people who turn on their car and put their automatic's immediately into reverse — he's seen cold AT fluid pressures jump from 300 to 900 — so if you have an automatic, let that tranny warm up before putting into reverse). 

CITY DRIVE CYCLE:  Now that the idle is complete, you can start to drive.  Drive normally for a couple of blocks:  no quick accelleration, no sloshing the gas in the gas tank and no going over 45mph.  Come to a stop.  Repeat 4 or 5 times.

FREEWAY CYCLE:  After the city drive cycle is finished accelerate on to a freeway.  Do not do a full open acceleration or this will cancel the drive cycle.  Get to a speed of 60 then go up and down between 65 and 55 for about a mile.  Pull over at the next exit and come to a stop for 30 secs.   Repeat.

You can now drive until you are done driving, going to work, doing errands, whatever.  Once you let the engine cool down to say 100 degrees or less the drive cycle will be complete.

The next time you start up the vehicle, you'll want to complete a drive cycle a second time.  Some vehicles, such as a BMW, need a third cycle to have everything reset correctly.

I did a search and discovered an explanation of a OBD II Drive Cycle here http://www.lyberty.com/car/drive-cycle.html

IMPORTANT:  If you have a post 1995 and you take it to the shop to get it repaired, make sure you have them do a drive cycle after they complete the work.  Roger told me a number of shops fail to do that.

Sigh .. I think I'm gonna purchase and drive only pre-72 vehicles .. I feel like I'm being watched!!!