Description of Drive Cycles

A drive cycle is a pattern of driving in which the Powertrain Control Module (PCM) will execute all of the OBD II diagnostic monitors. A drive cycle can be used by a technician to verify that a fault is present in a particular system, or to verify that a fault has been successfully repaired. A drive cycle may also be used to clear all of the Readiness Function Codes (RFCs) for use in emission certification (in some states).

The drive cycle consists of three distinct modes. Mode 1 is a procedure to learn the air/fuel ratio for a specific engine. The values acquired in Mode 1 are stored in a special part of the Keep Alive Memory (KAM) called the fuel table.

NOTE: If the battery is disconnected, or KAM is cleared, the air/fuel ratio will have to be relearned using the Mode 1 learning procedure.

Modes 2 and 3 are driving patterns that will exercise all of the noncontinuous monitors of the OBD II system. Mode 2 is used for Exhaust Gas Recirculation (EGR) and fuel system monitoring. Mode 3 is used for catalyst and Oxygen Sensor (O2S) monitoring.

The drive cycle procedures should be followed as precisely as possible to guarantee successful completion. Failure to accurately perform the procedures may result in ineffective testing and wasted time. Should the diagnostic monitors fail to complete when the tests have not been accurately performed, it will be necessary to repeat the tests before any concerns may be suspected. Very rough or slippery road surfaces may impact the ability to successfully complete the driving portions of the drive cycle.

NOTE: It is very important to complete Mode 1 before attempting to complete the Mode 2 and 3 driving procedures because the OBD II monitors will not complete until the fuel table is learned. Failure to complete Mode 1 will result in wasted time and possible incorrect diagnosis. If Mode 1 can not be completed with the recommended procedure, a vehicle concern may exist. Refer to Pinpoint Test QC to diagnose this concern. QC - OBD II Monitor Testing Not Complete (DTC P1000)