What is a drive cycle?

In a nutshell, a drive cycle is a series of driving patterns in a specific order needed for the vehicles PCM (Powertrain Control Module) to fully confirm the proper diagnosis and repairs were carried out. Every 1996 and newer vehicle requires this prior to passing the emissions portion of a Texas State Inspection. A vehicle will fail the emissions test even if the MIL (check engine light) is NOT illuminated. This is because the PCM knows that the drive cycle has not been completed. Times a drive cycle completion is needed:

-After unplugging a battery for any reason

-Clearing codes/MIL

Drive cycles vary by manufacturer and can be reset in as little as 20 miles by a qualified technician (like us) since we have the knowledge and experience but if the normal everyday driver just drives 75-100 miles like they normally would (a mix of highway and city driving) the drive cycle can be completed.

As you drive, monitors are being watched by you vehicles'' PCM and checked off as completed in a specific order. As they check off, they move on to the next monitor and do the same. If the PCM detects a problem within a monitored system, it may illuminate the MIL after one fault. Some monitors require a fault to happen twice within 40 start ups like in the evaporative emissions system before the PCM will illuminate the MIL. If you have left your gas cap off by accident but the MIL didn't illuminate until a day or two later, this is exactly why. Other monitors like the misfire monitor are continuously monitored and will illuminate the MIL almost instantly if a misfire of the engine occurs.

So the easiest thing to remember if you recently unplugged your battery or had work done that required the deleting of codes is to drive a minimum of 75-100 miles without the MIL illuminating and without having to jumpstart your battery. The more miles you put on the highway over 55mph (needed for catalytic converter and EGR monitors) the quicker the drive cycle will be completed. Just make sure to follow all safety laws and obey speed limits.