Arctic Cat 500 Sno Pro Operator'S/Performance Manual Download

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2. Air Temperature Sensor

3. Coolant Temperature Sensor

4. Throttle Position Sensor

5. Barometric Pressure Sensor

The fuel is first drawn into the electric fuel pump
through two pick-up valves and hoses. The fuel is then
routed through a high-pressure fuel hose to the fuel
rail.

The fuel pressure is maintained in the fuel rail by the
fuel regulator. With the fuel pressure maintained at a
constant psi, the ECU evaluates the information it
receives from the electrical sensors and opens the
injectors for precise periods of time (pulse widths) to
meet engine demands.



NOTE: The entire EFI system depends on all coils

functioning properly on the stator.

ECU

IO038A



NOTE: The ECU is coded with a letter. When

replacement of the ECU is necessary, the ECU
must be replaced with an ECU of the same code
letter.

The ECU is the brain of the EFI system. It uses sensor
inputs to determine the correct fuel/air ratio for the
engine given the existing conditions of altitude and
temperature.

If any of the sensors should fail while the engine is
running, the ECU will sense a problem and go into a
“fail safe” mode. This is an over-rich condition and
will greatly reduce performance. However, the engine
will be protected from a possible lean condition and
engine damage.

The ECU is equipped with a self-diagnostic system
utilizing the service icon in the speedometer/tachome-
ter and remains illuminated when a problem exists
with any of the sensors. The technician can determine
the problem sensor by reading the code shown on the
readout screen and applying it to the Diagnostic Codes
chart.



NOTE: The ECU cannot be repaired.

If the ECU is not receiving current from one of the
output coils on the stator, that circuit will not operate.
Coils on the stator are the charge coils operating the
ECU, the injector coil which operates the injectors, the
fuel pump coil which operates the fuel pump, and the
lighting coil/chassis control unit operating all accesso-
ries and the lighting system.

Air Temperature Sensor

This sensor detects air temperature entering the air
silencer and engine. The ECU sends current to this
sensor, and (depending on the temperature) the sensor
will pass a certain amount of current through the sen-
sor to ground. The ECU measures how much current
passes through the sensor to ground. From this mea-
surement, the ECU determines the air temperature and
calculates the fuel/air mixture ratio. This sensor is very
sensitive to temperature change. Resistance will drop
as the temperature rises.

Coolant Temperature Sensor

This sensor is very sensitive to temperature change.
The ECU measures the current flow through the sensor
to ground. From this measurement, the ECU can deter-
mine the engine coolant temperature and calculate the
correct fuel/air mixture ratio.



NOTE: If the coolant temperature rises above

80° C (176° F), the temperature sensor starts to
richen the fuel mixture. At this time, the check
engine light will flash constantly. Once the engine
coolant temperature reaches the specified temper-
ature 93° C (200° F), the temperature sensor will
signal the ECU to go into the rich mode to protect
the engine from overheating. At this time, the
check engine light will be constantly on.

Throttle Position Sensor

This sensor, located at the end of the throttle shaft, is a
potentiometer (essentially, a resistor). This sensor
transforms the throttle-valve position into output volt-
age to the ECU. In addition, the sensor detects the
opening or closing speed of the throttle valve and
feeds that rate of voltage change to the ECU.



NOTE: The input from the throttle position sen-

sor is one of the main inputs for the ECU calcula-
tion of fuel/air mixture ratio.

Ignition Timing Sensor

This sensor is located inside the magneto case next to
the flywheel, and the recoil starter and the flywheel
must be removed to access the sensor. This sensor is
triggered by a small metal disc precisely mounted to
the flywheel flange. Each time the disc rotates past the
sensor, a signal is sent to the ECU. From this signal,
the ECU determines ignition and injection timing and
RPM.