Equus 3150 - ABS/SRS + OBD2 Diagnostic Tool - Manual (Page 25)

Onboard Diagnostics
OBD2 MONITORS
OBD2 23
Non-Continuous Monitors
The other eight Monitors are “non-continuous” Monitors. “Non-
continuous” Monitors perform and complete their testing once per trip.
The “non-continuous” Monitors are:
Oxygen Sensor Monitor
Oxygen Sensor Heater Monitor
Catalyst Monitor
Heated Catalyst Monitor
EGR System Monitor
EVAP System Monitor
Secondary Air System Monitor
Air Conditioning (A/C) Monitor
The following provides a brief explanation of the function of each Monitor:
Comprehensive Component Monitor (CCM) - This Monitor
continuously checks all inputs and outputs from sensors,
actuators, switches and other devices that provide a signal to the
computer. The Monitor checks for shorts, opens, out of range value,
functionality and “rationality.”
Rationality: Each input signal is compared against all other
inputs and against information in the computer’s memory to see
if it makes sense under the current operating conditions.
Example: The signal from the throttle position sensor indicates
the vehicle is in a wide-open throttle condition, but the vehicle is
really at idle, and the idle condition is confirmed by the signals
from all other sensors. Based on the input data, the computer
determines that the signal from the throttle position sensor is not
rational (does not make sense when compared to the other
inputs). In this case, the signal would fail the rationality test.
The CCM may be either a “One-Trip” or a “Two-Trip” Monitor,
depending on the component.
Fuel System Monitor - This Monitor uses a Fuel System
Correction program, called Fuel Trim, inside the on-board
computer. Fuel Trim is a set of positive and negative values that
represent adding or subtracting fuel from the engine. This program is
used to correct for a lean (too much air/not enough fuel) or rich (too
much fuel/not enough air) air-fuel mixture. The program is designed to
add or subtract fuel, as needed, up to a certain percent. If the correction
needed is too large and exceeds the time and percent allowed by the
program, a fault is indicated by the computer.
The Fuel System Monitor may be a “One-Trip” or “Two-Trip” Monitor,
depending on the severity of the problem.