Smog cert fault resets
 

How do you get the OBD systems to reset on a ‘97 911 in order to pass smog test?

Buy cheap scan tool and reset the trouble codes.

I had this problem, although on an ‘06 Toyota. I had just replaced the battery so all old data was lost. Smog guy told me to go out and drive on the freeway at steady speeds for 45 minutes or so to regenerate the data. It worked and I passed...

That would be the first version of the OBD2. You need to clear all codes with a scanner, and do a drive cycle. The drive cycle consists of mostly driving like a grandma on the freeway for an extended amount of time.

You need to clear any codes then complete a "drive cycle," as mentioned above.

From stone cold, usually overnight will do the trick.

Start engine, idle cold for approx. 2 min, 10 secs.

Accelerate to 20-30 MPH, Maintain steady speed for approx 3 min, 15 secs.

Accelerate to 40-60 MPH, Maintain steady speed for approx 15 mins.

Decelerate and come to a stop. Idle in gear for approx 5 mins.

Do NOT let the engine rev over 3K rpm.
Do NOT make large throttle angle changes.
Do NOT go over 60mph.
Obviously, don't turn the key off or stall the engine when completing the drive cycle.

And to run the evap flag, the gas tank needs to be between 1/4 and 3/4 full, IIRC.

If all of the flags do not clear after the drive cycle, repeat it. If one won't reset, like the catalyst flag, it's probably that it's borderline and the computer wants to check it a few more times before making a decision.

Correct.

Correct.

Set!

The process may require three trips with a cold start between trips.

Set!

Read here under Porsche 993 Cycle Flag Basics; https://www.systemsc.com/codes.htm