Electric Fan
The electric cooling fan is controlled by the ECM. The ECM uses a remote power output final stage (mounted on the fan housing).
The power output stage receives power from a 50 amp fuse (located in glove box above the fuse bracket). The electric fan is controlled by a pulse width modulated signal from the ECM.
The fan is activated based on the ECM calculation (sensing ratio) of:
- Coolant outlet temperature
- Calculated (by the ECM) catalyst temperature
- Vehicle speed
- Battery voltage
- Air Conditioning pressure (calculated by IHKA and sent via the K-Bus to the ECM)
Activation of the electric fan:
When the vehicle is first started the fan is activated briefly (20% of maximum speed), then it is switched off. This procedure is performed for diagnostic purposes.
The voltage generated by the fan when it slows down (it becomes a generator at this time) must meet the power output stages programmed criteria. This will confirm the RPM of the fan, if this is not met the signal wire from the output stage is switched to ground and a fault is set in memory.
After the initial test has been performed, the fan is brought up to the specified operating speed. At 10% (sensing ratio) the fan runs at 1/3 speed. At a sensing ratio of between 90-- 95% the fan is running at maximum speed. Below 10% or above 95% the fan is stationary.
The sensing ratio is suppressed by a hysteresis function, this prevents speed fluctuation. When the A/C is switched on, the electric fan is not immediately activated.
After the engine is switched off, the fan may continue to operate at varying speeds (based on the ECM calculated catalyst temperature). This will cool the radiator down form a heat surge (up to 10 minutes).