Engine Cooling Fan

Engine Cooling Fan:

PURPOSE
The ECM controls an electric engine cooling fan to maintain engine operating temperature. The ECM uses the following input signals to determine fan speed operation:
- engine speed signal (from RPM sensor)
- vehicle speed signal (from speedometer)
- A/C temperature control setting
- A/C system pressure

LOCATION
Cooling fan - in front of radiator
Fan relay - On relay shelf, top of radiator

OPERATION
The fan is a two-speed unit. Low speed is used to control normal operating conditions. High speed is used only if engine over-heating is immanent or if A/C system pressure is too high.

The fan is started when engine coolant temperature exceeds the normal operating limit of 216° F (102° C) or if ECM internal temperature exceeds 176° F (80° C).

With A/C the fan operates when:
- the A/C is "ON" and vehicle speed low
- A/C system pressure is high

When engine is stopped the fan operates:
- for 6 minutes if the engine was running at high load and high temperature immediately before being switched off.
- for 3 minutes if the fan was running at full speed when the engine stopped