Diagnostic Aids
The Visctronic Drive Fan (VDF) clutch consists of three main elements:
- A working chamber.
- A reservoir chamber.
- A fan speed sensor.
A fluid port valve controls the fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, "shearing" of the fluid will result in fan rotation. The valve is activated via a Pulse Width Modulated (PWM) output signal from the PCM. By opening and closing the fluid port valve, the PCM can control fan speed. Fan speed is monitored through a Hall-Effect sensor and is monitored by the PCM during closed loop operation. The PCM will optimize fan speed based on Engine Coolant Temperature (ECT), Transmission Fluid Temperature (TFT), or Intake Air Temperature (IAT) requirements. When an increased demand for fan speed is requested for vehicle cooling, the PCM will monitor the fan speed through the Hall-Effect sensor. If a fan speed increase is required, the PCM will output the PWM signal to the fluid port, providing the required fan speed increase.
During KOEO Self-Test, the PCM commands 100% duty cycle. A DTC is set 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 calibrated value.
This test is intended to diagnose the following:
- Visctronic drive fan clutch.
- Fan speed sensor.
- Harness circuits.
- PCM.