• Leak Detection Pump
• Low Speed Fan Relay
• MTV Actuator
• Proportional Purge Solenoid
• SRV Valve
• Speed Control Relay
• Speed Control Vent Relay
• Speed Control Vacuum Relay
• 8 Volt Output
• 5 Volt Output
Based on inputs it receives, the powertrain control
module (PCM) adjusts fuel injector pulse width, idle
speed, ignition timing, and canister purge operation.
The PCM regulates the cooling fans, air conditioning
and speed control systems. The PCM changes gener-
ator charge rate by adjusting the generator field.
The PCM adjusts injector pulse width (air-fuel
ratio) based on the following inputs.
• Battery Voltage
• Intake Air Temperature Sensor
• Engine Coolant Temperature
• Engine Speed (crankshaft position sensor)
• Exhaust Gas Oxygen Content (heated oxygen
sensors)
• Manifold Absolute Pressure
• Throttle Position
The PCM adjusts engine idle speed through the
idle air control motor based on the following inputs.
• Brake Switch
• Engine Coolant Temperature
• Engine Speed (crankshaft position sensor)
• Park/Neutral (transmission gear selection)
• Transaxle Gear Engagement
• Throttle Position
• Vehicle Speed (from Transmission Control Mod-
ule)
The PCM adjusts ignition timing based on the fol-
lowing inputs.
• Intake Air Temperature
• Engine Coolant Temperature
• Engine Speed (crankshaft position sensor)
• Knock Sensor
• Manifold Absolute Pressure
• Park/Neutral (transmission gear selection)
• Transaxle Gear Engagement
• Throttle Position
The automatic shut down (ASD) and fuel pump
relays are mounted externally, but turned on and off
by the powertrain control module through the same
circuit.
The camshaft and crankshaft signals are sent to
the powertrain control module. If the PCM does not
receive both signals within approximately one second
of engine cranking, it deactivates the ASD and fuel
pump relays. When these relays are deactivated,
power is shut off to the fuel injectors, ignition coils,
fuel pump and the heating element in each oxygen
sensor.
The PCM contains a voltage converter that
changes battery voltage to a regulated 8.0 volts. The
8.0 volts power the camshaft position sensor, crank-
shaft position sensor and vehicle speed sensor. The
PCM also provides a 5.0 volts supply for the engine
coolant temperature sensor, intake air temperature
sensor, manifold absolute pressure sensor and throt-
tle position sensor.
The PCM engine control strategy prevents reduced
idle speeds until after the engine operates for 320 km
(200 miles). If the PCM is replaced after 320 km (200
miles) of usage, update the mileage in new PCM. Use
the DRB scan tool to change the mileage in the PCM.
Refer to the appropriate Powertrain Diagnostic Man-
ual and the DRB scan tool.
AUTOMATIC SHUTDOWN (ASD) SENSE—PCM
INPUT
DESCRIPTION
It is an input to the Powertrain Control Module
from the rely in the Power Distribution Center, refer
to the cover for relay location.
OPERATION
The ASD sense circuit informs the PCM when the
ASD relay energizes. A 12 volt signal at this input
indicates to the PCM that the ASD has been acti-
vated. This input is used only to sense that the ASD
relay is energized.
When energized, the ASD relay supplies battery
voltage to the fuel injectors, ignition coils and the
heating element in each oxygen sensor. If the PCM
does not receive 12 volts from this input after
grounding the ASD relay, it sets a Diagnostic Trouble
Code (DTC).
When energized, the ASD relay provides power to
operate the injectors, ignition coil, generator field, O2
sensor heaters (both upstream and downstream), and
also provides a sense circuit to the PCM for diagnos-
tic purposes. The PCM energizes the ASD any time
there is a Crankshaft Position sensor signal that
exceeds a predetermined value. The ASD relay can
also be energized after the engine has been turned
off to perform an O2 sensor heater test, if vehicle is
equipped with OBD II diagnostics.
With SBEC III, the ASD relay’s electromagnet is
fed battery voltage, not ignition voltage. The PCM
still provides the ground. As mentioned earlier, the
PCM energizes the ASD relay during an O2 sensor
heater test. This test is performed only after the
engine has been shut off. The PCM still operates
internally to perform several checks, including moni-
toring the O2 sensor heaters. This and other DTC
LH FUEL SYSTEM 14 - 27
DESCRIPTION AND OPERATION (Continued)
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