OBD Drive Cycle

According to the New York DMV, the correct drive cycle varies with your car's make and model and with the monitor that has to be reset. A general cycle won't work on every car, so if your monitors still aren't ready after a few tries, the cycle made for your make and model may be what you need.

For the New York DMV's generic cycle, keep the tank between half and three-quarters full.

A cold start means starting the car hours after it was last driven. The New York inspection program's universal cycle calls for coolant below 122°F and close to the outside air temperature.

The simplest way to reach that point is to park the car overnight. The Ohio EPA version calls for the car to rest for 8 hours before you begin.

The cycle below comes from the New York DMV. Choose a safe stretch of road where traffic won't force you to brake while you hold highway speed.

1. Start the car cold, once it has been sitting for several hours.
2. Let it idle in drive for 2.5 minutes, keeping the air conditioning and rear defroster switched on.
3. Hold 55 mph without speeding up or slowing down for 3 minutes.
4. If traffic allows it safely, take your foot off the gas and let the car slow itself to 20 mph, without touching the brake or the clutch.
5. Cruise at a steady speed somewhere between 55 and 60 mph for 5 minutes.

The Ohio EPA's generic cycle is a bit different:

1. Let the car rest for 8 hours.
2. Spend at least 10 minutes driving at 55 mph or faster.
3. Spend at least 20 minutes in stop-and-go city traffic, with a minimum of 4 stops that let the car idle.

Ohio EPA shares a drive cycle taken from a Ford owner's manual. It calls for the car to sit at least 8 hours, followed by a 15-minute stretch of steady highway driving and then a 20-minute stretch of stop-and-go driving that includes four 30-second idles.

On GM vehicles, the catalyst monitor can need 5 full drive cycles to set once the battery has been disconnected.

Per the New York inspection program, ordinary driving over a few days, mixing city and highway miles, is usually enough to get the monitors ready. Ohio EPA recommends at least 2 to 3 days of driving, covering both highway and city miles, once codes have been cleared or the battery disconnected.

After the battery has been disconnected, it can take several days or even weeks for all the monitors to finish. A handy rule of thumb: if the car has covered under about 200 miles since a battery swap or a code clearing, some monitors are probably still not ready.

Not every monitor has to be ready. Under EPA guidance that most states follow, how many can be unset varies by the year the car was made.

So if your 2012 car shows 2 monitors not ready, keep driving until one more sets. Under that guidance, a 1999 car with two monitors not ready meets the readiness rule, but California allows only one unfinished monitor on 1996 to 1999 gas cars. California has its own rule: a 2000 or newer gas car can pass with one monitor not ready only if that monitor is the evaporative (fuel vapor) one.