DIAGNOSIS AND TESTING - ELECTRONICLY
CONTOLLED VISCOUS FAN DRIVE
NOISE
NOTE: It is normal for fan noise to be louder (roaring)
when:
² Fan duty cycle high. This may occur when ambient
(outside air temperature) is very high.
² Engine loads and temperatures are high such as
when towing a trailer.
² Cool silicone fluid within the fan drive unit is
being redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.
LEAKS
Viscous fan drive operation is not affected by small
oil stains near the drive bearing. If leakage appears
excessive, replace the fan drive unit.
ELECTRONICALLY CONTROLLED VISCOUS DRIVE
If the fan assembly free-wheels without drag (the
fan blades will revolve more than five turns when
spun by hand), replace the fan drive. This spin test
must be performed when the engine is cool.
For the following test, the cooling system must be
in good condition. It also will ensure against excessively
high coolant temperature.
The Electronic Viscous Fan drive can be tested
using the DRB III scan tool.
(1) Set the parking brake and verify the transmission
is in park or neutral.
(2) Stat and allow engine to reach normal operating
termeratures.
(3) With engine idling, connect the DRB III and
select appropraite model year and engine option.
(4) Lacate and select actuator tests, then select
PWM Viscous Fan.
(5) Monitor fan speed and duty cycle; verify that
the fan speed increments are proportional to the duty
cycle precentage during the actuation event.
CAUTION: Some engines equipped with serpentine
drive belts have reverse rotating fans and viscous
fan drives. They are marked with the word
REVERSE to designate their usage. Installation of
the wrong fan or viscous fan drive can result in
engine overheating.
CAUTION: If the viscous fan drive is replaced
because of mechanical damage, the cooling fan
blades should also be inspected. Inspect for fatigue
cracks, loose blades, or loose rivets that could
have resulted from excessive vibration. Replace fan
blade assembly if any of these conditions are
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