Enabling Conditions— The following conditions
must typically be met before the PCM runs the cat-
alyst monitor. Specific times for each parameter may
be different from engine to engine.
•
Accumulated drive time
•
Enable time
•
Ambient air temperature
•
Barometric pressure
•
Catalyst warm-up counter
•
Engine coolant temperature
•
Accumulated throttle position sensor
•
Vehicle speed
•
MAP
•
RPM
•
Engine in closed loop
•
Fuel level
Pending Conditions—
•
Misfire DTC
•
Front Oxygen Sensor Response
•
Front Oxygen Sensor Heater Monitor
•
Front Oxygen Sensor Electrical
•
Rear Oxygen Sensor Rationality (middle check)
•
Rear Oxygen Sensor Heater Monitor
•
Rear Oxygen Sensor Electrical
•
Fuel System Monitor
•
All TPS faults
•
All MAP faults
•
All ECT sensor faults
•
Purge flow solenoid functionality
•
Purge flow solenoid electrical
•
All PCM self test faults
•
All CMP and CKP sensor faults
•
All injector and ignition electrical faults
•
Idle Air Control (IAC) motor functionality
•
Vehicle Speed Sensor
•
Brake switch
•
Intake air temperature
Conflict— The catalyst monitor does not run if
any of the following are conditions are present:
•
EGR Monitor in progress
•
Fuel system rich intrusive test in progress
•
EVAP Monitor in progress
•
Time since start is less than 60 seconds
•
Low fuel level
•
Low ambient air temperature
Suspend— The Task Manager does not mature a
catalyst fault if any of the following are present:
•
Oxygen Sensor Monitor, Priority 1
•
Upstream Oxygen Sensor Heater, Priority 1
•
EGR Monitor, Priority 1
•
EVAP Monitor, Priority 1
•
Fuel System Monitor, Priority 2
•
Misfire Monitor, Priority 2
NON-MONITORED CIRCUITS
OPERATION
The PCM does not monitor all circuits, systems
and conditions that could have malfunctions causing
driveability problems. However, problems with these
systems may cause the PCM to store diagnostic trou-
ble codes for other systems or components. For exam-
ple, a fuel pressure problem will not register a fault
directly, but could cause a rich/lean condition or mis-
fire. This could cause the PCM to store an oxygen
sensor or misfire diagnostic trouble code.
The major non-monitored circuits are listed below
along with examples of failures modes that do not
directly cause the PCM to set a DTC, but for a sys-
tem that is monitored.
FUEL PRESSURE
The fuel pressure regulator controls fuel system
pressure. The PCM cannot detect a clogged fuel
pump inlet filter, clogged in-line fuel filter, or a
pinched fuel supply or return line. However, these
could result in a rich or lean condition causing the
PCM to store an oxygen sensor or fuel system diag-
nostic trouble code.
SECONDARY IGNITION CIRCUIT
The PCM cannot detect an inoperative ignition coil,
fouled or worn spark plugs, ignition cross firing, or
open spark plug cables.
CYLINDER COMPRESSION
The PCM cannot detect uneven, low, or high engine
cylinder compression.
EXHAUST SYSTEM
The PCM cannot detect a plugged, restricted or
leaking exhaust system. It may set a EGR or Fuel
system fault or O2S.
FUEL INJECTOR MECHANICAL MALFUNCTIONS
The PCM cannot determine if a fuel injector is
clogged, the needle is sticking or if the wrong injector
is installed. However, these could result in a rich or
lean condition causing the PCM to store a diagnostic
trouble code for either misfire, an oxygen sensor, or
the fuel system.
EXCESSIVE OIL CONSUMPTION
Although the PCM monitors engine exhaust oxygen
content when the system is in closed loop, it cannot
determine excessive oil consumption.
THROTTLE BODY AIR FLOW
The PCM cannot detect a clogged or restricted air
cleaner inlet or filter element.
25 - 20
EMISSION CONTROL SYSTEMS
NS
DESCRIPTION AND OPERATION (Continued)
