period the switch ratio reaches a predetermined
value, a counter is incremented by one. The monitor
is enabled to run another test during that trip. When
the test fails 6 times, the counter increments to 3, a
malfunction is entered, and a Freeze Frame is stored,
the code is matured and the MIL is illuminated. If
the first test passes, no further testing is conducted
during that trip.
The MIL is extinguished after three consecutive
good trips. The good trip criteria for the catalyst
monitor is more stringent than the failure criteria. In
order to pass the test and increment one good trip,
the downstream sensor switch rate must be less than
45% of the upstream rate. The failure percentages
are 59% respectively.
Enabling ConditionsÐThe 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.
²Accumulated drive time
²Enable time
²Ambient air temperature
²Barometric pressure
²Catalyst warm-up counter
²Engine coolant temperature
²Vehicle speed
²MAP
²RPM
²Engine in closed loop
²Fuel level
Pending ConditionsÐ
²Misfire DTC
²Front Oxygen Sensor Response
²Front Oxygen Sensor Heater Monitor
²Front Oxygen Sensor Electrical
²Rear Oxygen Sensor Rationality (middle check)
²Rear Oxygen Sensor Heater Monitor
²Rear Oxygen Sensor Electrical
²Fuel System Monitor
²All TPS faults
²All MAP faults
²All ECT sensor faults
²Purge flow solenoid functionality
²Purge flow solenoid electrical
²All PCM self test faults
²All CMP and CKP sensor faults
²All injector and ignition electrical faults
²Idle Air Control (IAC) motor functionality
²Vehicle Speed Sensor
²Brake switch (auto trans only)
²Intake air temperature
ConflictÐThe catalyst monitor does not run if any
of the following are conditions are present:
²EGR Monitor in progress (if equipped)
²Fuel system rich intrusive test in progress
²EVAP Monitor in progress²Time since start is less than 60 seconds
²Low fuel level-less than 15 %
²Low ambient air temperature
²Ethanol content learn is taking place and the
ethanol used once flag is set
SuspendÐThe Task Manager does not mature a
catalyst fault if any of the following are present:
²Oxygen Sensor Monitor, Priority 1
²Oxygen Sensor Heater, Priority 1
²EGR Monitor, Priority 1 (if equipped)
²EVAP Monitor, Priority 1
²Fuel System Monitor, Priority 2
²Misfire Monitor, Priority 2
OPERATION - NON-MONITORED CIRCUITS
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, fuel system, or mis-
fire diagnostic 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. The misfire will however,
increase the oxygen content in the exhaust, deceiving
the PCM in to thinking the fuel system is too lean.
Also see misfire detection.
CYLINDER COMPRESSION
The PCM cannot detect uneven, low, or high engine
cylinder compression. Low compression lowers O2
content in the exhaust. Leading to fuel system, oxy-
gen sensor, or misfire detection fault.
EXHAUST SYSTEM
The PCM cannot detect a plugged, restricted or
leaking exhaust system. It may set a EGR (if
equipped) or Fuel system or O2S fault.
RSEMISSIONS CONTROL25-5
EMISSIONS CONTROL (Continued)
