Powertrain
The powertrain has electronic controls to reduce exhaust emissions while maintaining
excellent driveability and fuel economy. The engine control module (ECM) is the control
center of this system. The ECM monitors numerous engine and vehicle functions. The
ECM constantly looks at the information from various sensors and other inputs, and
controls the systems that affect vehicle performance and emissions. The ECM also performs
the diagnostic tests on various parts of the system. The ECM can recognize operational
problems and alert the driver with the malfunction indicator lamp (MIL). When the
ECM detects a malfunction, the ECM stores a diagnostic trouble code (DTC). The problem
area is identified by the particular DTC that is set. Review the components and wiring
diagrams in order to determine which systems are controlled by the ECM.
The following are some of the functions that the ECM controls:
| • | The ignition control (IC) |
| • | The knock sensor (KS) system |
| • | The evaporative emissions (EVAP) system |
| • | The cooling fan control |
Engine Control Module Function
The ECM constantly looks at the information from various sensors and other inputs
and controls systems that affect vehicle performance and emissions. The ECM also performs
diagnostic tests on various parts of the system. The ECM can recognize operational
problems and alert the driver with the malfunction indicator lamp (MIL). When the
ECM detects a malfunction, the ECM stores a diagnostic trouble code (DTC). The
problem area is identified by the particular DTC that is set. The input and output
devices in the ECM include analog-to-digital converters, signal buffers, counters,
and output drivers. The output drivers are electronic switches that complete a ground
or voltage circuit when turned on. Most ECM controlled components are operated by
output drivers. The ECM monitors these driver circuits for proper operation and, in
most cases, can set a DTC corresponding to the controlled device if a problem is detected.
Malfunction Indicator Lamp (MIL) Operation
The malfunction indicator lamp (MIL) is located in the instrument panel
cluster. The MIL will display as either SERVICE ENGINE SOON or one of
the following symbols when commanded ON:
The MIL indicates that an emissions related fault has occurred
and vehicle service is required.
The following is a list of the modes of operation for the MIL:
| • | The MIL illuminates when the ignition is turned ON, with the engine
OFF. This is a bulb test to ensure the MIL is able to illuminate. |
| • | The MIL turns OFF after the engine is started if a diagnostic
fault is not present. |
| • | The MIL remains illuminated after the engine is started if the
control module detects a fault. A diagnostic trouble code (DTC) is stored
any time the control module illuminates the MIL due to an emissions
related fault. The MIL turns OFF after three consecutive ignition
cycles in which a Test Passed has been reported for the diagnostic
test that originally caused the MIL to illuminate. |
| • | The MIL flashes if the control module detects a misfire condition
which could damage the catalytic converter. |
| • | When the MIL is illuminated and the engine stalls, the MIL will
remain illuminated as long as the ignition is ON. |
| • | When the MIL is not illuminated and the engine stalls, the MIL
will not illuminate until the ignition is cycled OFF and then ON. |
Warm-up Cycle
The ECM uses warm-up cycles to run some diagnostics and to clear any diagnostic
trouble codes (DTCs). A warm-up cycle occurs when the engine coolant temperature
increases 22°C (40°F) from the start-up temperature. The engine coolant
must also achieve a minimum temperature of 71°C (160°F). The ECM counts
the number of warm-up cycles in order to clear the malfunction indicator lamp (MIL).
The ECM will clear the DTCs when 40 consecutive warm-up cycles occur without a
malfunction.
Diagnostic Trouble Codes (DTCs)
The ECM is programmed with test routines that test the operation of the various
systems the ECM controls. Some tests monitor internal ECM functions. Many tests are
run continuously. Other tests run only under specific conditions, referred to as Conditions
for Running the DTC. When the vehicle is operating within the conditions for running
a particular test, the ECM monitors certain parameters and determines if the values
are within an expected range. The parameters and values considered outside the range
of normal operation are listed as Conditions for Setting the DTC. When the Conditions
for Setting the DTC occur, the ECM executes the Action Taken When the DTC Sets.
Some DTCs alert the driver via the MIL or a message. Other DTCs do not trigger
a driver warning, but are stored in memory. The ECM also saves data and input
parameters when most DTCs are set. This data is stored in the Freeze Frame and/or
Failure Records.
The DTCs are categorized by type. The DTC type is determined by the MIL operation
and the manner in which the fault data is stored when a particular DTC fails. In
some cases there may be exceptions to this structure. Therefore, when diagnosing the
system it is important to read the Action Taken When the DTC Sets and the Conditions
for Clearing the DTC in the supporting text .
There are different types of DTCs and different actions taken when the DTCs
set. Refer to Diagnostic Trouble Code (DTC) Type Definitions for a description of
the general characteristics of each DTC type.
