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Car Problems? NG900 or old 9-3 Only If you're experiencing problems with your NG900 or 9-3, post your question in here. CEL Code or GTFO!

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Old 05-08-2006, 01:42 PM   #1
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GM ODBII DRIVE CYCLE (please sticky)

When you cut power to your ECU, or if you get a CEL and have it cleared, the On Board Diagnostics needs to run a series of tests to ensure emissions compliance. This is why you usually need to drive around for a few days or so after clearing a CEL.

If you follow the Drive Cycle listed below, you can cut the time needed to reset OBDII...

GENERAL MOTORS OBD II "Drive Cycle"

Most OBD II ("On-Board Diagnostics II") diagnostic monitors will run at some time during normal operation of the vehicle. 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 50°C (122°F) and within 6°C (11°F) 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.

Reprinted on http://www.obdii.com/drivecycle.html courtesy of General Motors Corporation
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Old 05-08-2006, 08:17 PM   #2
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really good INFO...x2 on the sticky
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Old 05-09-2006, 05:26 AM   #3
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yeah this is great, since I think I will have a new ECU like 1 week before I have to get inspected.
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Old 05-09-2006, 06:50 AM   #4
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Now to find a clear stretch of highway to do this around D.C.
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Old 03-05-2009, 07:33 PM   #5
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really depends on the year of vehicle saabs are different 96-98 ng900 non turbo cars are the hardest to set im readyness test....requires the tech 2 and 1 1/2 hours of driving the car at different speeds....watching the engines load...speed .....engine rpm....its like drivin the car with an egg under your throttle pedal....only motronic obd2 cars...
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Old 03-05-2009, 08:06 PM   #6
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wait, what?
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Old 12-29-2010, 11:29 AM   #7
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I just got my '99 9-3 SE smog completed successfully after an initial failure, due to CEL for a bad oxygen sensor. There are a few things worth knowing about this GM OBD2 Drive Cycle, and using it to flip your OBD2 Readiness Monitors to "Ready" or "Complete" so you can take your vehicle to the Smog Center and have it pass the test.

1) The GM cycle described above varies from vehicle to vehicle. Every manufacturer seems to have some leeway on how this drive cycle is implemented, and they vary the cycle a little differently on each model. For example, here is the Saab implementation of this Drive Cycle for the 1996-1998 900s:

http://www.swedecar.com/images/photo...ve%20cycle.pdf

As you can see, the cycle is much more extensive in some ways than the standard one that GM makes available.

Generally, it's tough to find the procedure for a given vehicle. I never could find one for my 9-3, and I don't think it's the same as the one above for the 900 series. I don't think the dealers want that information public.

2) There are a total of 11 available sensors that can be included in an OBD2 vehicle and used as readiness monitors, but no vehicle produced uses all 11. Most use around 7. In your OBD2 diagnostic software, it should show which monitors your vehicle is equipped with, and which are "Not Available". On the 9-3, the readiness monitor sensors are: Misfire, Fuel System, Components, Catalyst, Evap System (for Fuel), O2 Sensor, O2 Sensor Heater.

3) Even if one or two of your readiness monitors are "Not Ready" or "Not Complete", you can still pass your test. Different states have different requirements for different vehicles, but for some cars, they allow a pass with up to two monitors not being ready.

4) Some posts I've read list some additional requirements for the OBD2 Drive Cycle that I did not see included in the GM list. I cannot confirm any of these as being important.
-The fuel tank must be between 3/4 full and 1/4 full or the tests will not run.
-There is a cool-down cycle that should be completed when the car is parked after the drive, idling for 2-5 minutes. I would recommend a 5 minute cycle, to be safe.
-You cannot exceed 60 MPH or 3000 engine RPMs during the course of a cold-start drive, or the cycle resets and you have to wait until the next cold start to re-attempt the cycle. Too much throttle angle variance can also cause a reset.

5) Not all the procedures have to be done at the same time. Some procedures must be repeated twice. Again, this is only on certain vehicles.

6) So far as I can tell, the original procedure was developed by BMW, as below.

http://srlx.com/p-car/obdii_readiness.pdf

7) Here's one account of an experience with the OBD2 drive cycle.

Vin Suprynowicz » Blog Archive » ?They can?t tell you you?re going to fail. He has to run it?

According to this account, the smog technician may know if you're going to fail the test, but by law, they cannot tell you because the EPA, and State entities responsible for air quality like the California Air Resources Board, want to keep track of the failures, for statistics, or to make a little extra cash, or whatever. Some places will charge $100 or more to run your particular vehicle through the Drive Cycle. Some claim it's not necessary to pay a technician, but just drive your car from a cold start in the morning, first thing, onto the freeway and off it for 30 minutes or so, and you should be fine. That's what I did, and it worked for me.

8. I used Ian Hawkins' TORQUE software on an Android phone, coupled with an ELM 327 Bluetooth OBD2 Interface, to check my readiness monitors. I detail how to do this elsewhere on this site. Highly recommended. I would not recommend attempting the drive cycle unless you had such software to monitor (graph) your RPM and throttle, and check the monitors, because the test is so particular and if you violate the 3000 RPM threshold, even for a moment, you can screw up the procedure and force a do-over. It's real easy to violate that 3000 RPM threshold in first gear, and I found myself sometimes wondering if I had or had not done so. With the Torque software, it's captured in a graph.
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Last edited by tronbrain; 12-29-2010 at 11:51 AM.
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Old 12-29-2010, 11:47 AM   #8
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A highly informative post. Thanks.
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Old 12-29-2010, 11:53 AM   #9
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To be clear, I HAD a CEL (Check-Engine Light) for a bad oxygen sensor, which I then replaced. Once the sensor was confirmed as working, I cleared the OBD2 fault codes, both logged and pending. THAT is what reset all my readiness monitors to "Not Ready" and caused my initial smog test failure, not the CEL. The smog guy wouldn't even test me with the CEL active, said it was a mandatory failure and I had to get that fixed first.

The smog guy was cool and gave me a discount on the re-test, told me beforehand that the vehicle would pass this time so I didn't have to risk another failure.
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Old 12-29-2010, 12:08 PM   #10
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A highly informative post. Thanks.
Thanks. I am glad I was able to put all the information together in a single place. Hopefully it will save the next punter the trouble of having to research it all. Took me bloody two hours to figure it out, and even then, it was not a definite solution. But I got lucky and it worked for me.

Again, that Torque software is fantastic. I'm giving it another plug here:

http://www.saablink.net/forum/car-en...htm#post801814
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