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How the Fiero cooling Fan sytems works

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Coolant Sensor

Is your Fiero running a bit hot these days?  Understand how the Fiero cooling fan system works can help you to quickly know if the cooling fan system is working properly.

The first step is making sure the cooling fan turns on when it should.

Here is how the Fiero cooling fan system works.

The Enine Control Module (ECM) provides a ground path to energize the fan relay, which turns ON the cooling fan.  The ECM will command the fan ON, when coolant temp is above 108°C (226°F).  When the engine cools down to about 101°C (213°F), the ECM de-energizes the fan relay, and the fan stops.  If the coolant sensor fails (code 14 or 15 set) the ECM will command fan constant ON. 

A/C equipped vehicles have a separate signal wiring to the ECM for a fan control.  When the A/C control switch is on, and the low pressure switch closes, the ECM receives a signal on this line and turns on the fan.  The A/C clutch does not have to be in gauge for the ECM to turn the ON the fan.


  1. If the Fiero Gauge or Warning Light indicates overheating, but no boil over occurred, the gauge circuit should be checked.  If you have a SCAN tool, the accuracy can be checked by comparing the coolant sensor reading using the SCAN tool and comparing its reading with the gauge reading.
  2. If the engine is actually overheating and the Fiero Gauge, or Warning Light indicates overheating, but the cooling fan is not coming on, the coolant sensor has probably shifted out of calibration and should be replaced.