The Auto Shutdown (ASD) relay provides battery
voltage to the ignition coil. The PCM provides a
ground contact (circuit) for energizing the coil. When
the PCM breaks the contact, the energy in the coil
primary transfers to the secondary causing the
spark. The PCM will de-energize the ASD relay if it
does not receive the crankshaft position sensor and
camshaft position sensor inputs. Refer to Auto Shutdown
(ASD) Relay—PCM Output, in this section for
relay operation.

The Auto Shutdown (ASD) and fuel pump relays
are located in the Power Distribution Center (PDC).
The camshaft position sensor and crankshaft position
sensor signals are sent to the PCM. If the PCM
does not receive the signal within approximately 1
second of engine cranking, it deactivates the ASD
relay and fuel pump relay. When these relays are
deactivated, power is shut off from the fuel injectors,
ignition coils, oxygen sensor heating elements and
fuel pump.
The PCM contains a voltage converter that
changes battery voltage to a regulated 5 volts direct
current to power the camshaft position sensor, crankshaft
position sensor, manifold absolute pressure sensor,
throttle position sensor, A/C pressure switch, A/C
pressure transducer, and vehicle speed sensor.

ENGINE START-UP MODE
This is an OPEN LOOP mode. If the vehicle is in
park or neutral (automatic transaxles) or the clutch
pedal is depressed (manual transaxles) the ignition
switch energizes the starter relay when the engine is
not running. The following actions occur when the
starter motor is engaged.
² If the PCM receives the camshaft position sensor
and crankshaft position sensor signals, it energizes
the Auto Shutdown (ASD) relay and fuel pump relay.
If the PCM does not receive both signals within
approximately one second, it will not energize the
ASD relay and fuel pump relay. The ASD and fuel
pump relays supply battery voltage to the fuel pump,
fuel injectors, ignition coil, (EGR solenoid and PCV
heater if equipped) and heated oxygen sensors.
² The PCM energizes the injectors (on the 69°
degree falling edge) for a calculated pulse width until
it determines crankshaft position from the camshaft
position sensor and crankshaft position sensor signals.
The PCM determines crankshaft position within
1 engine revolution.
² After determining crankshaft position, the PCM
begins energizing the injectors in sequence. It adjusts
injector pulse width and controls injector synchronization
by turning the individual ground paths to the
injectors On and Off.
² When the engine idles within ±64 RPM of its
target RPM, the PCM compares current MAP sensor
value with the atmospheric pressure value received
during the Ignition Switch On (zero RPM) mode.
Once the ASD and fuel pump relays have been
energized, the PCM determines injector pulse width
based on the following:
² MAP
² Engine RPM
² Battery voltage
² Engine coolant temperature
² Inlet/Intake air temperature (IAT)
² Throttle position
² The number of engine revolutions since cranking
was initiated
During Start-up the PCM maintains ignition timing
at 9° BTDC.