Equus 3110 - CanOBD2 Diagnostic Tool - Manual (Page 26)

24 CAN OBD2
E
Onboard Diagnostics
OBD 2 MONITORS
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, actu-
ators, switches and other devices that provide a signal to the comput-
er. The Monitor checks for shorts, opens, out of range value, function-
ality 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 indi-
cates 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, depend-
ing on the component.
Fuel System Monitor - This Monitor uses a Fuel System Cor-
rection program, called Fuel Trim, inside the on-board comput-
er. Fuel Trim is a set of positive and negative values that represent
adding or subtracting fuel from the engine. This program is used to cor-
rect 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 sub-
tract 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.