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GENERAL INFORMATION
3.0 SYSTEM DESCRIPTION AND
FUNCTIONAL OPERATION
3.1 GENERAL DESCRIPTION
These Sequential Fuel Injection (SFI) engine sys-
tems have the latest in technical advances. The
OBDII/Euro Stage III OBD diagnostics incorpo-
rated with the Powertrain Control Module (PCM)
are intended to assist the field technician in repair-
ing vehicle problems by the quickest means.
3.2 FUNCTIONAL OPERATION
3.2.1
FUEL CONTROL
The PCM controls the air/fuel ratio of the engine
by varying fuel injector on time. Mass air flow is
calculated using the speed density method using
enigne speed, manifold absolute pressure, and air
temperature change.
Different fuel calculation strategies are used de-
pending on the operational state of the engine.
During crank mode, a longer pulse width fuel pulse
is delivered followed by fuel pulses determined by a
crank time strategy. Cold engine operation is deter-
mined via an open loop strategy until the O2
sensors have reached operating temperature. At
this point, the strategy enters a closed loop mode
where fuel requirements are based upon the state of
the O2 sensors, engine speed, MAP, throttle posi-
tion, air temperature, battery voltage, and coolant
temperature.
3.2.2 ON-BOARD DIAGNOSTICS
The PCM has been programmed to monitor many
different circuits of the fuel injection system. This
monitoring is called on-board diagnosis.
Certain criteria, or arming conditions, must be
met for a trouble code to be entered into the PCM
memory. The criteria may be a range of: engine rpm,
engine temperature, and/or input voltage to the
PCM. If a problem is sensed with a monitored
circuit, and all of the criteria or arming conditions
are met, then a trouble code will be stored in the
PCM.
It is possible that a trouble code for a monitored
circuit may not be entered into the PCM memory
even though a malfunction has occurred. This may
happen because one of the trouble code criteria have
not been met.
The PCM compares input signal voltages from
each input device with specifications (the estab-
lished high and low limits of the range) that are
programmed into it for that device. If the input
voltage is not within specifications and other trou-
ble code criteria are met, a trouble code will be
stored in the PCM memory.
The On Board Diagnostics have evolved to the
second Generation of Diagnostics referred to as
OBDII/Euro Stage III OBD. These OBDII/Euro
Stage III OBD Diagnostics control the functions
necessary to meet the requirements of California
OBDII, Federal OBD regulation and European reg-
ulation. These requirements specify the inclusion of
a Malfunction Indicator Light (MIL) located on the
instrument panel. The purpose of the MIL is to
inform the vehicle operator in the event of a mal-
function of any emission system or component.
MIL Lamp Strategy
I/M Readiness OK to test = Key On Engine OFF
– MIL Lamp will remain on until the vehicle is
started or Ignition is turned off.
I/M not ready for testing = Key On Engine OFF
– MIL Lamp on solid for (15) seconds then MIL
Lamp will flash on/off for (5) seconds then it will
remain on until the vehicle is started or the Ignition
is turned off.
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