Description of Drive Cycles

A drive cycle is a pattern of driving in which the Powertrain Control Module (PCM) will execute all of the On Board Diagnostics II (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).

DRIVE CYCLE MODES
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 EGR and fuel system monitoring.
- Mode 3 is used for catalyst and oxygen sensor monitoring.

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.
Also: Verifying A Repair (Drive Cycle)