36
M54engMS43/ST036/6/2000
ELECTRIC FAN
The electric cooling fan is now controlled by the ECM. The ECM uses a remote power out-
put 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 calcula-
tion (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)
NOTE: If the ECM indicates a fault check the fan for freedom of movement
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 from a heat
surge (up to 10 minutes).
OUTPUT STAGE
MS42.0
POWER
MS 43.0
