Equus 3110 - CanOBD2 Diagnostic Tool - Manual (Page 30)

28 CAN OBD2
E
Onboard Diagnostics
OBD 2 MONITORS
The oxygen sensor must reach a temperature of at least 600-650°F,
and the engine must reach normal operating temperature, for the
computer to enter into closed-loop operation. The oxygen sensor only
functions when the computer is in closed-loop. A properly operating
oxygen sensor reacts quickly to any change in oxygen content in the
exhaust stream. A faulty oxygen sensor reacts slowly, or its voltage sig-
nal is weak or missing.
The oxygen sensor is a “Two-Trip” monitor. If a fault is found on the first
trip, the computer temporarily saves the fault in its memory as a
Pending Code. The computer does not command the MIL on at this
time. If the fault is sensed again on the second trip, the computer com-
mands the MIL “On,” and saves the code in its long-term memory.
Secondary Air System Monitor - When a cold engine is first
started, it runs in open-loop mode. During open-loop operation,
the engine usually runs rich. A vehicle running rich wastes fuel and
creates increased emissions, such as carbon monoxide and some
hydrocarbons. A Secondary Air System injects air into the exhaust
stream to aid catalytic converter operation:
1. It supplies the catalytic converter with the oxygen it needs to oxidize
the carbon monoxide and hydrocarbons left over from the combus-
tion process during engine warm-up.
2. The extra oxygen injected into the exhaust stream also helps the
catalytic converter reach operating temperature more quickly dur-
ing warm-up periods. The catalytic converter must heat to operat-
ing temperature to work properly.
The Secondary Air System Monitor checks for component integrity and
system operation, and tests for faults in the system. The computer runs
this Monitor once per trip.
The Secondary Air System Monitor is a “Two-Trip” monitor. If a fault is
found on the first trip, the computer temporarily saves this fault in its
memory as a Pending Code. The computer does not command the
MIL on at this time. If the fault is sensed again on the second trip, the
computer commands the MIL “On,” and saves the code in its long-term
memory.