Peteheard, what do you mean by "overheating"?
The conditions for fans coming on are bit complicated:
"Stage 1 Fan Operation
The large cooling fan operation is enabled with the ECM via circuit 335 energises the Engine Cooling Fan Relay 1 (R7). When the negative terminal is connected to ground through Engine Cooling Fan Relay 1 (R7), the large cooling fan (right) operates.
The ECM determines when to enable the Engine Cooling Fan Relay 1 (R7), based on inputs from the A/C request signal, Engine Coolant Temperature sensor (ECT) and Vehicle Speed Sensor (VSS)
Condititions for stage 1 cooling fan engagement
The ECM turns Engine Cooling Fan Relay 1 (R7) ON when:
* Air conditioning request indicated (YES) and the vehicle speed is less then 30kph
*Air conditioning pressure is greater then 1,500kPa
*Coolant temperature is greater then 104 C or
*an ECT sensor failure is detected by the ECM.
When the ignition switch is turned from ON to OFF and the engine coolant temperature is above 117C the ECM will continue to energise the Engine Cooling Fan Relay 1 (R7) for approximately four minutes.
The ECM turns Engine Cooling Fan Relay 1 (R7) OFF when the following conditions have been met;
*Air conditioning request not indicated (NO) and the coolant temperature is less then 99C or
*Air conditioning request indicated (YES) with pressure less than 1,700kPa, vehicle speed greater than 50kph and coolant temperature less then 99C
Stage 2 Fan Operation
The small (left) cooling fan operation is enabled when the ECM via circuit 473 energises the Engine Cooling Fan Relay 2 (R5). When the negative terminal is connected to earth via the Engine Cooling Fan Relay 2 (R5), the small cooling fan operates. Both cooling fans are now operational, the large fan via the Engine Cooling Fan Relay 1 (R7) and the small cooling fan via Engine Cooling Relay 2 (R5)
Conditions for Stage 2 Fan Operation
The ECM determines when to enable the Engine Cooling Fan Relay 2 (R5), based on inputs from the ECT sensor.
The ECM turns Engine Cooling Fan Relay 2 (R5) ON if the Engine Cooling Fan Relay 1 (R7) has been energised for one second and the following conditions have been met:
*if there is a ECM message response fault, setting a DTC (P1258)
*The ECM detects an ECT sensor failure
*Engine coolant temperature is above 108C, or
*Air conditioning pressure is greater than 2000kPa
Note - if the large engine cooling fan is off when the criteria for turning the small engine cooling fan on are first met, the small engine cooling fan will turn on 5 seconds after the large engine cooling fan is switched on.
If both the large and small cooling fans are enabled, the ECM turns the small engine cooling fan OFF via Engine Cooling Fan Relay 2 when,
*The engine coolant temperature is less than 103C,and
*Air conditioning request is not indicated (NO) OR
*Air conditioning request is indicated (YES) and the pressure is less than 1500kPa"