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Old 12-29-2010, 11:29 AM   #7
tronbrain
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Location: Los Angeles, CA
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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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1999 Saab 9-3 SE Stock / 155K miles

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Last edited by tronbrain; 12-29-2010 at 11:51 AM.
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