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OBD-II Driving Cycle

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Around the end of Septermber 1999, Nate Johnson posted the following on the DML:

From: Nate [natedak2k@yahoo.com]
Subject: DML: Failed Emissions (a little long)


Hey all, just wanted to know if anyones had this problem! A buddy of mine drives a '97 4X4 Auto. He took it in for emmisions insp. last week and failed miserably! The only mod he's done is a drop in K&N filter. They asked him if he'd disconnected the battery anytime in the near past and yes he had (can't remember why.) They told him that more than likely the computer had dumped some settings when he did this and that's why it wouldn't pass. They gave him a little instruction sheet that led him through a series of steps he had to perform while running his truck to make his puter "relearn" some emissions settings. Something like start it with AC on, run at a certain RPM in N for 1 minute, drive at a certain speed for a certain amount of time, accelerate WOT to a certain speed, etc../... etc../... (He's got the instruction sheet at home and is gonna give me a copy if anyones interested.) He went out on the road, did what the sheet said, came back and they retested his emissions. He passed with flying colors!

As it turns out, that instruction sheet was the OBD-II driving cycle, which is contained herein. If you have to deal with emissions testing where you live, it might not hurt to run through this thing beforehand to give yourself a little edge. :-)

A complete driving cycle should perform diagnostics on all systems. A complete driving cycle can be done in under fifteen minutes. To perform an OBDII Driving cycle do the following:

  1. Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50C (122F) and within 6C (11F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

  2. Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.

  3. Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

  4. Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

  5. Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

  6. Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55- 60mph). This will perform the same diagnostics as in step 3.

  7. Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

  8. Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

Many thanks to Nate Johnson (natedak2k@yahoo.com) and Bernd D. Ratsch (bernd@texas.net) for supplying the above info!
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Jon N. Steiger / jon@dakota-truck.net