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OBDII - The comprehensive DO's and DON'Ts to clear your flags
If your battery has been disconnected, you are most certainly going to have to reset all your OBDII flags for smog check.
Your car might be running perfectly but if you don't reset your OBDII flags with this archaic procedure, you will repeatedly fail.
Over the past 15 years of owning my 993, I have had to execute the Porsche drive cycle approximately every other year to prepare my vehicle for smog check in California. I have had varying success and failure and decided to make an even more comprehensive direction list to follow.
Referee stations no longer allow you to get a sign off. Driving the car a few hundred miles does not work.
I most recently failed to clear my flags after 4 late-evening attempts and then got it to work on the 5th attempt. When the flags did clear, I was gently reminded of what has and has not worked over the past decade and a half.
1) Get an OBDII reader that you plug into your OBDII port by the drivers side right knee. I recommend:
This reader will tell you when your flags have been reset and you are ready to go for smog check.
2) Do the drive late at night so you can flow it as interrupted as possible. Have a timer handy so you know you have met your triggers. It is okay if the drive cycle is interrupted during the procedure... It's cumulative. as long as you DON'T: - Turn off the car
- Exceed 60 MPH
- Exceed 3000 RPM
3) The drive cycle is as follows: - Start the car and idle for 2min10sec
- Drive the car between 20mph and 30mph for 3min15sec
- Drive the car between 40mph and 60mph for 15min
- Come to stop and idle in neutral for 5min
4) Do not go into Reverse. Prepare the car the day/night before by making sure you do not need to go into reverse. Back into the garage or park in the driveway so you can drive straight out. Reverse may cancel the drive cycle.
5) Do not use cruise control. I believe this is the repeated mistake that I make every other year.
6) Do the drive cycle when the car is cold. If you have driven the car in 4 hours before you attempt the drive cycle, it will not work.
7) When you plug in the OBDII, you will likely have 3 solid circles and about 7 that blink. The yellow ? light will be illuminated and the OBDII reader will beep about every 30 seconds. The blinking flags will ALL reset at the same time. They DO NOT reset one at a time. It's all or nothing. And when they do reset, the OBDII green light with the check mark illuminates.
8) Even if you do everything perfect, it is likely it can take 2x to do this process. Don't bother trying to do it back to back. It won't work. Go home, park the car and try it again the next night. (Don't forget to park the car so you don't have to reverse the next night.) - You might get lucky and it will clear the flags the first time you do it... But don't count on it.
Once you get the green light.. You are good to smog.
So remember:
1) Car should be cold
2) No not go into reverse
3) Do not use cruise control
4) Do not exceed 60 mph
5) Do not exceed 3000 RPM
6) All flags go from blinking to solid at the same time when cycle is complete and the OBDII reader goes from yellow to green light
7) It is okay to stop and go (traffic lights, etc.) the drive cycle is cumulative.
8) It will likely take 2x of doing the drive cycle to clear the flags
That's 15 years of research.... Print this out, store it in your car with an OBDII reader. You will forget in two years what the detailed instructions are. You will find other posts that don't have ALL the information and you will make many of the mistakes I made.
And pass the OBDII and instructions to the new buyer should you ever sell the car.
I think the key is the 20-30 mph for 3 minutes that is the clincher. It verifies the O2s so is probably crucial to the rest of the cycle, and I found it was the hardest one to do on a public road. I have only had to do this once, and it worked first time.
I believe someone had suggested that one should have their emergency flashers on so as not to make people behind you too angry. I live in the mountains and would do the drive at four in the morning. No one on the road here at that time except for all the deer.
I believe someone had suggested that one should have their emergency flashers on so as not to make people behind you too angry. I live in the mountains and would do the drive at four in the morning. No one on the road here at that time except for all the deer.
Yup... That's what I do. First attempt, I was driving in the right hand lane at 20mph with the flashers on.. A lady pulls up next to me in a Prius and asks, "Are you okay?"
Nice write up bline. I'd ad 2 things. I think you need a minimum of 2 cold starts. 2. DOn't disconnect your battery for the month leading up to your inspection and drive at least 2x a week. THis has worked for me (3x) and never had to do this scary drive cycle stuff it's all been set. i.e buy that fancy 3 spoke, wait until after your inspection to install , not the week before etc...
The key point to setting the monitors is that you must have completed a minimum
of two trips that include two cold starts. The problem for all that don't have an
access to a Porsche tester is when to end the first trip. If that trip is ended too
soon, the trip is a wasted trip, i.e. you've wasted all your driving time.
The proper term to use is "set" and not "reset", as you would set-up your new
cell phone and reset (to its default state) your old cell phone when you sell it.
When I had to do this a couple of years ago, I ended up doing the BMW cycle, which may be the same as yours, I can't remember, and it worked a charm. I had to reverse out of my garage before starting the (successful) cycle.
^^ My OBD reader tells me what flags are set and which are not. Do you mean while driving? I have never tried that.
If your flags need to be set... Meaning the car is not ready for an emissions test because you have disconnected the battery...
When you plug in the OBDII reader, it will show certain flags as solid (3 of them) and the other flags blink. All of the blinking flags continue to blink until the drive cycle is complete... At which time, the flags that were blinking all go solid at the same time. The yellow question mark light also switches to the green check light at that time.
-- Again, I'm referencing what happens if your car is running properly but your flags have not been set for OBDII smog check. I'm sure if there is a problem with the car, the flags would indicate something other.
When I had to do this a couple of years ago, I ended up doing the BMW cycle, which may be the same as yours, I can't remember, and it worked a charm. I had to reverse out of my garage before starting the (successful) cycle.
To be honest... I couldn't tell you for sure that reversing the car is a problem. I had read that on this forum in a few different places so I included it in my instructions.
After you have done the drive cycle 5x in a few weeks, you'll try just about anything to get those flags to set.. Even if it's standing on your head while eating a hot dog.
My hunch is... The only reason my drive cycle didn't work the first 3x was because I kept using the cruise control. I still positioned my car so I didn't have to reverse just to eliminate any triggers that might negate the cycle... Even if it might just be a old-wives tail.
I have done this drive cycle thing so many times over my 15 years of owning this 993... And I always seem to forget the little details like:
Don't use cruise control AND all flags go solid at the same time..
That's why I made this thread.. Let my experience save you time.
Nice write up bline. I'd ad 2 things. I think you need a minimum of 2 cold starts. 2. DOn't disconnect your battery for the month leading up to your inspection and drive at least 2x a week. THis has worked for me (3x) and never had to do this scary drive cycle stuff it's all been set. i.e buy that fancy 3 spoke, wait until after your inspection to install , not the week before etc...
I'm w JB on this one. I just had the battery out for 6+ months, put it back in and drove the car a bit over a month, month and a half. On test day I took a 30 min drive running her at high RPMs to warm her up and passed flying colors. In the previous 7 yearly tests, my well used car would get started cold and driven 5 blocks to the test station and pass.
I forgot that a lot of 993's don't have cruise control... I think that's why it rarely comes up in the conversation regarding the drive cycle.. I guess I'm one of the few owners that has the "speed control" option.
lol.
Thanks! Best thread I've read on this topic. I live in a condo and I finally managed to find an outlet I can sneak around a neighbors car to keep the charger on. It seems there are 3 codes that clear easily but the others require all these driving parameters.
08-13-2015, 03:35 PM
OBDII - The comprehensive DO's and DON'Ts to clear your flags
