Cooling Fan 'Stages'

[QuackHandle]

I'm chasing an annoying problem with my Monaro VXR;

A few days ago it overheated, and the air con had stopped working a few weeks prior as well. At first I thought the two were unrelated and that my thermostat was faulty. However I've removed and tested the stat, and it's functioning perfectly.

Using an OBD reader I can see that when the coolant temp reaches 108°C, both cooling fans activate, but having looked at the workshop manuals I can see that there are meant to be two 'stages' that the fans operate in, the first stage should kick in at 98°C but they aren't... Interestingly one of the other conditions for Stage 1 fan operation is that there is an AC request.
(I'll paste the exact wording from the manuals below).

All relevant relays have been tested, the fans themselves do spin when receiving power, and when Stage 2 kicks in both fans spin, wiring to the fans themselves has been checked, and theres also no sign of the common melted connectors.

From my interpretation of the info below I can rule out low AC pressure, as leaving the car stationary to get hotter than 98°C does not activate Stage 1.

Has anyone else had this issue?

Thanks in advance

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The cooling fans operate in two stages; in both stages both fans run.
In stage 1 the two fan motors are connected in series so both fans run at low speed.
In stage 2 each fan motor is connected to battery supply so both fans run at high speed.

Conditions for Stage 1 operation are:
- There is an A/C request and: the vehicle speed is less than 30 km/h or; the A/C refrigerant pressure is greater than 1500 kPa or;
- The engine coolant temperature is greater than 98 °C or;
- The engine coolant temperature is greater than 113 °C when the engine is switched off
(in this case stage 1 will operate for approximately four minutes - this is referred to as low fan run-on) or;
- An ECT sensor fault is detected and a DTC such as P0117, P0118, P1114 or P1115 is set.

Stage 1 operation will cease when:
- There is no A/C request and the engine coolant temperature is less than 95 °C or;
- There is an A/C request and the vehicle speed is greater than 50 km/h and the A/C pressure is less than 1170 kPa and
the engine coolant temperature is less than 95 °C or;
- The vehicle speed is greater than 104 km/h.


The conditions for stage 2 operation are:
- The A/C refrigerant pressure is greater than 2400 kPa or;
- The engine coolant temperature is greater than 108 °C or;
- An ECT sensor fault is detected and a DTC such as P0117, P0118, P1114 or P1115 is set.
- There is a BCM message response fault, which will cause a PIM DTC B2002 to set.

If stage 1 operation is off when the conditions for stage 2 operation are met, stage 2 operation will be initiated 5s after initiation of stage 1 operation.

Stage 2 operation will cease and revert to stage 1 operation when:
- The engine coolant temperature is less than 102 °C and; there is no A/C request or;
there is an A/C request and the A/C refrigerant pressure is less than 1900 kPa or:
- The vehicle speed is greater than 104 km/h.

Edited by QuackHandle on Thursday 21st August 12:50

[Lincsls1]

So, it seems the engine coolant sensor is working because your OBD reader is able to tell the temperature from it.
How have you tested the low fan speed relay? Sometimes things fail or breakdown under load, but can seem to work when bench tested.
Is it worth throwing a new low speed relay on? I don't suppose its the same as the high speed relay?