DeVille DTS V8-4.6L VIN 9 (2002)
to indicate the torque output of the powertrain. This signal, referred to as the Delivered Torque signal, is used by the EBCM to determine the required
action when the EBCM sees the front wheels slipping. The EBCM may decide to apply the front brakes only, or apply the front brakes and signal the
PCM to reduce the torque output of the powertrain. The EBCM requests reduced torque using another PWM signal. This signal, referred to as the
Desired Torque signal, is used by the PCM to determine the amount of torque reduction requested by the EBTCM. The PCM adjusts the ignition timing
in response to the Desired Torque signal.
The Desired Torque signal varies within a range of 95 percent and 5 percent duty cycle. A duty cycle at 95 percent indicates no torque reduction. A
duty cycle at 10 percent indicates full torque reduction. The Desired Torque signal to the PCM is normally a 90 percent duty cycle. The EBCM will
decrease the duty cycle of the signal by the amount of torque reduction desired. The PCM responds to the signal by adjusting the ignition timing. The
PCM may shut off the fuel to one or more cylinders unless the following conditions are present:
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The coolant temperature is below -40°C (-40°F) or above 131°C (268°F).
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A low coolant level is present.
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The engine speed is below 600 RPM.
The PCM will re-enable the fuel injectors as the need for traction control ends.
Traction control will be disable when certain DTCs set. The PCM will request a TRACTION OFF light/message via class 2 serial data when the DTCs
set.
Data Link Connector (DLC)
The Data Link Connector (DLC) provides a class 2 data circuit that allows bi-directional communication between the scan tool, the PCM, and other
system control modules. Usually located under the instrument panel, the DLC provides power and ground for the scan tool. Some common uses of the
scan tool are listed below:
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Identifying stored Diagnostic Trouble Codes (DTCs)
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Clearing DTCs
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Performing output control tests
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Reading serial data for diagnostic analysis
Service Engine Soon/Malfunction Indicator Lamp (MIL)
The Service Engine Soon/Malfunction Indicator Lamp (MIL) is located in the Instrument Panel Cluster (IPC). The MIL is controlled by the PCM and is
used to indicate that the PCM has detected a problem that affects vehicle emissions, may cause powertrain damage, or severely impacts driveability.
Diagnostic Trouble Codes (DTCS)
The PCM is programmed with test routines that check the operation of the various systems the PCM controls. Some tests check internal PCM 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 PCM checks certain parameters and determines whether or not the values are within an
expected range. Which parameters and what values are considered outside the range of normal operation are listed as Conditions for Setting the DTC.
When the Conditions for Setting the DTC are true, the PCM 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. Refer to the DTC Type Table for a complete list of PCM DTCs and
what driver alerts they trigger. The PCM also saves data and input parameters when most DTCs are set. This data is stored in Freeze Frame and/or
Failure Records.
DTCs are categorized by type. The DTC type relates to how the MIL operates and how the fault data is stored when a particular DTC fails. In some
cases there may be exceptions to this structure. Therefore, reading the Action Taken When the DTC Sets and Conditions for Clearing the MIL(DTC in
the supporting text when diagnosing the system is important.
The following list describes the general characteristics of each DTC type:
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Type A DTCs are emissions related. The PCM performs the following actions at the time of the first fail:
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Turns on the MIL
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Stores the DTC in memory
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Captures Freeze Frame/Failure Records data
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Type B DTCs are emissions related. The first fail and any subsequent failures are handled differently.
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The PCM performs the following actions at the time of the first fail:
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Does not turn on the MIL
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Stores the DTC in memory as Failed Last Test
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Captures Freeze Frame/Failure Records data
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The PCM performs the following actions at the time of the second fail if the fault is active for 2 consecutive driving cycles:
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Turns on the MIL
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Stores the DTC in memory (the DTC will now appear in History)
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Updates Freeze Frame/Failure Records data
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The PCM performs the following actions at the time of a second failure that is not on a consecutive trip:
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Does not turn on the MIL
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Stores the DTC in memory as Failed Last Test
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Updates Failure Records data only
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Type C DTCs are not emissions related. The PCM performs the following actions at the time of the first fail:
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Does not turn on the MIL
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Stores the DTC in memory
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Captures Failure Records data
