Aurora V8-4.0L VIN C (1996)
Powertrain Control Module: Description and Operation
Powertrain Control Module (PCM)
DESCRIPTION
The powertrain used in this vehicle consists of a dual overhead cam engine mated to a 4T80E electronically controlled transaxle. It has controls to
reduce exhaust emissions while maintaining excellent driveability and fuel economy. The Powertrain Control Module (PCM) is the heart of this
control system.
The Control Module refers to the Powertrain Control Module (PCM) and the Vehicle Control Module (VCM). The control module is designed to
maintain exhaust emission levels to Federal or California standards while providing excellent driveability and fuel efficiency. Review the components
and wiring diagrams in order to determine which systems are controlled by each specific control module. The control module monitors numerous
engine and vehicle functions. The control module controls the following operations:
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Fuel control
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Ignition Control (IC)
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Knock Sensor (KS) system
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Automatic transmission shift functions
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Cruise Control Enable
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Generator
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Evaporative Emission (EVAP) Purge
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A/C Clutch Control
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Cooling Fan Control
Control Module Function
The Control Module supplies a buffered voltage to various sensors and switches. The input and output devices in the control module include an
analog to digital converters, signal buffers, counters, and special drivers. The Control Module controls most components with electronic switches
which complete a ground circuit when turned ON. These switches are arranged in groups of 4 and 7 called one of the following:
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Quad Driver Module
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Output Driver Modules
The surface mounted Quad Driver Module can independently control up to 4 outputs (Control Module) terminals. The Output Driver Modules can
independently control up to 7 outputs. Not all outputs are always used.
Torque Management
Torque Management is a function of the PCM that reduces engine power under certain conditions. Torque management is performed for three
reasons:
1. To prevent overstress of powertrain components.
2. To limit engine power when brakes are applied.
3. To prevent damage to the vehicle during certain abusive maneuvers.
The PCM uses manifold vacuum, intake air temperature, spark retard, engine speed, engine coolant temperature, A/C clutch status, and EGR valve
position to calculate engine output torque. It then looks at torque converter status, transaxle gear ratio, and brake switch inputs and determines if
any torque reduction is required. If torque reduction is required, the PCM retards spark as appropriate to reduce engine torque output. In the case
of abusive maneuvers, the PCM may also shut off fuel to certain cylinders to reduce engine power.
There are five instances when engine power reduction is likely to be experienced
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During transaxle upshifts and downshifts.
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Heavy acceleration from a standing start.
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If brakes are applied with moderate to heavy throttle.
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When the driver is performing stress-inducing (abusive) maneuvers such as shifting into gear at high throttle angles.
In the first two instances, the driver is unlikely to even notice the torque management actions. In the other cases, engine power output will be
moderate at full throttle.
When the PCM determines that engine power reduction is required, it calculates the amount of spark retard necessary to reduce power by the
desired amount. This spark retard is then subtracted from the current spark advance. In the case of abusive maneuvers, the fuel injectors for
cylinders 1, 4, 6, and 7 will also be disabled for a period of time.
