User guide

56 www.AutoEnginuity.com
the misfire is detected and then illuminate normally. This is a "One-
Trip" monitor. See also Misfire.
Non-Continuous Monitor
A monitor that runs a specific test at the manufacturer’s designated
interval. See also One- or Two-Trip Monitor.
One-Trip Monitor
A non-continuous monitor that requires only a single fault to be
detected before the engine computer illuminates the MIL and
places a DTC in the stored DTC area of the engine computer’s
memory. See also Two-Trip Monitor or Trip.
Open Loop
When some or all of the components of the engine computer are not
in their normal operational condition, the engine computer will use
pre-determined, or default, values to regulate the fuel mixture and
spark advance. Typically, this happens when a vehicle starts as cer-
tain components are not yet up to operating temperature (i.e., oxy-
gen sensors).
O2 or Oxygen Sensor
The oxygen sensor is the heart and soul of the fuel system. It is
sometimes referred to as the Exhaust Gas Oxygen or Lambda sen-
sor. Typically oxygen sensors are positioned before and after the
catalytic converter in the exhaust pipe. The oxygen sensors sample
the exhaust and report back a value in terms of voltage. The engine
computer looks at the voltage to determine if the fuel/air mixture is
lean or rich, and adjusts the amount of fuel entering the engine
accordingly. Because of the time delay for the engine computer to
correct the fuel mixture, and the time it takes for the oxygen sensor
to report, the oxygen sensor switches from lean to rich frequently.
Oxygen sensors located before the catalytic converter will exhibit
the most switching (crosscounts). The oxygen sensors located after
the catalytic converter should exhibit flat or relatively low signal
amplitude. The OBD-II standard allows oxygen sensors that do not
influence the lean to rich fuel trim to not report their data. A good
pre-catalytic oxygen sensor should switch between the values of 1
volt for a rich mixture, and .1 volt for a lean mixture.