But why? Are they viscous clutches?
Yes It is Viscous Electronic
I Actually replaced one because my manager at the time said to, and it made no difference.
The Newer Calibrations seem to do it more though.
Here's the Description and Pinpoint test:
AH3 : CHECK THE COOLING FAN OPERATION
NOTE: Inherent to viscous clutches is a delay in transitioning from a low to a high speed or from a high to a low speed. This delay is dependent upon engine speed, starting fan speed and clutch temperature. With the engine at operating temperature
and at 2,500 RPM, the delay should be less than 30 seconds.
NOTE: The time required to change fan speed, once a command is issued by the PCM,
varies depending on operating conditions such as temperature, engine speed and starting fan speed.
The reaction time can be from seconds to several minutes depending on the test
NOTE: The calibration limits the engine RPM when using output state control. The engine
RPM must be increased using the accelerator pedal to reach the required RPM for this test.
Ignition ON, engine running.
Access the PCM and monitor the FANSS (RPM) PID.
Access the PCM and monitor the RPM (RPM) PID.
Engine at normal operating temperature.
Increase the engine speed to 2,500 RPM using the accelerator pedal.
Access the PCM and control the FANDC (PER) PID.
Decrease the commanded cooling fan duty cycle to 0%.
Allow the fan speed to stabilize below 600 RPM.
The cooling fan and viscous drive actuator valve controls the fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, shearing of the fluid results in fan rotation. The valve is activated by a pulse width modulation (PWM) output signal from the powertrain control module (PCM). By opening and closing the fluid port valve, the PCM controls the fan speed. Fan speed is measured through a Hall effect sensor, and is monitored by the PCMduring closed loop operation. The PCM optimizes the fan speed based on the engine coolant temperature, the engine oil temperature, the fuel rail temperature, the transmission fluid temperature, the intake air temperature, or air conditioning requirements.
When an increased demand for fan speed is requested for vehicle cooling, the PCM monitors the fan speed through
the Hall effect sensor. If a fan speed increase is required, the PCM outputs the PWM signal to the
fluid port, providing the required fan speed increase. During the key on, engine running (KOER)
self-test, the PCM commands a 100% duty cycle. A DTC sets if the PCM detects the voltage on
the valve control circuit is not within the expected range or if the fan speed is less than a