Manual

Onboard Diagnostics
OBD2 MONITORS
22 OBD2
 If the conditions that caused the MIL to light are no longer present
for the next three trips in a row, the computer automatically turns the
MIL “Off” if no other emissions-related faults are present. However,
the DTCs remain in the computer’s memory as a history code for 40
warm-up cycles (80 warm-up cycles for fuel and misfire faults). The
DTCs are automatically erased if the fault that caused them to be
set is not detected again during that period.
 Misfire and fuel system faults require three trips with “similar
conditions” before the MIL is turned “Off.” These are trips where the
engine load, RPM and temperature are similar to the conditions
present when the fault was first found.
After the MIL has been turned off, DTCs, Freeze Frame data,
and manufacturer-specific enhanced data stay in the
computer’s memory. Most of the enhanced data can only be
retrieved with special equipment such as a Scan Tool.
 Erasing the DTCs from the computer’s memory can also turn off the
MIL. See ERASING DIAGNOSTIC TROUBLE CODES (DTCs) on
page 54, before erasing codes from the computer’s memory. If a
Code Reader or Scan Tool is used to erase the codes, Freeze
Frame data as well as other manufacturer-specific enhanced data
will also be erased.
OBD2 MONITORS
To ensure the correct operation of the various emissions-related
components and systems, a diagnostic program was developed and
installed in the vehicle’s on-board computer. The program has several
procedures and diagnostic strategies. Each procedure or diagnostic
strategy is made to monitor the operation of, and run diagnostic tests on,
a specific emissions-related component or system. These tests ensure
the system is running correctly and is within the manufacturer’s
specifications. On OBD2 systems, these procedures and diagnostic
strategies are called “Monitors.”
Currently, a maximum of eleven Monitors are used in OBD2 systems.
Additional monitors may be added as a result of Government
regulations as the OBD2 system grows and matures. Not all vehicles
support all eleven Monitors.
Monitor operation is either “Continuous” or “Non-Continuous,”
depending on the specific monitor.
Continuous Monitors
Three of these Monitors are designed to constantly monitor their
associated components and/or systems for proper operation.
Continuous Monitors run constantly when the engine is running. The
Continuous Monitors are:
Comprehensive Component Monitor (CCM)
Misfire Monitor
Fuel System Monitor