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 Shut-
down (ASD) Relay—PCM Output, in this section for
relay operation.
The coil’s low primary resistance (0.4 - 0.6 ohm)
allows the PCM to fully charge the coil for each fir-
ing. There are coil capacitor added to each bank of
cylinders for radio noise suppression.
AUTOMATIC SHUTDOWN (ASD) AND FUEL PUMP
RELAYS
The PCM operates the ASD relay and fuel pump
relay through one ground path. The PCM operates
them by switching on and off the ground path for the
solenoid side of the relays. Both relays turn on and
off at the same time.
The ASD relay connects battery voltage to the fuel
injectors and ignition coils. The fuel pump relay con-
nects battery voltage to the fuel pump.
The PCM turns the ground path off when the igni-
tion switch is in the Off position. Both relays are off.
When the ignition switch is in the On or Crank posi-
tion, the PCM monitors the crankshaft position sen-
sor
and
camshaft
position
sensor
signals
to
determine engine speed and ignition timing. If the
PCM does not receive a crankshaft position sensor
signal and camshaft position sensor signal when the
ignition switch is in the Run position, it de-energizes
both relays. When the relays de-energize, battery
voltage is not supplied to the fuel injectors, ignition
coil and fuel pump.
The ASD relay and fuel pump relay are located in
the Power Distribution Center (PDC) near the bat-
tery (Fig. 8). A decal on the underside of the PDC
cover shows the locations of each relay and fuse con-
tained in the PDC.
CRANKSHAFT POSITION SENSOR
The crankshaft position sensor detects slots cut
into the transmission driveplate extension. There are
3 sets of slots. Two set contain 4 slots and one set
contains 5 slots, for a total of 13 slots (Fig. 9). Basic
timing is set by the position of the last slot in each
group. Once the Powertrain Control Module (PCM)
senses the last slot, it determines crankshaft position
(which piston will next be at TDC) from the camshaft
position sensor input. It may take the PCM one
engine revolution to determine crankshaft position.
The PCM uses crankshaft position reference to
determine injector sequence and ignition timing.
Fig. 6 Coil Capacitor
Fig. 7 Coil Capacitor
Fig. 8 Power Distribution Center
8D - 4
IGNITION SYSTEM
300M
DESCRIPTION AND OPERATION (Continued)