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[terry paget]

You can also make a test lead using the fan loom from the seized car...

Good tip. I think it's a different socket. I unplugged the socket easily on the 08 car, today trying to salvage the fan off the seized 04 car it was a nightmare unplugging it. Will check in the morning.

[Nick W]

You could also simply connect the fan motor to the battery

I did say that. A powerprobe makes powering stuff like motors whether on the car or on the bench quick and easy. It also enables you to add power or another earth which makes for efficient diagnosis of wiring/connector issues. They basic ones like in the link are cheap enough that if you do simple electrical work it will quickly pay for itself in time and reduced hassle. You do need to be careful using one in modern systems though.

[plym ian]

The astra is it a petrol or diesel? And what year is it?

[terry paget]

The astra is it a petrol or diesel? And what year is it?

It's a 2008 Astra H 2008 manual.

[terry paget]

The astra is it a petrol or diesel? And what year is it?

It's a 2008 Astra H 2008 manual.

Petrol

[dave the builder]

The coolant temperature sensor on the wet thermostat is to send temperature information to the engine ecu . the engine ecu decides IF the fan should be on and activates relays to power the plug at the bottom of the fan shroud ,
that plug is a fan speed resistor , depending on how hot then rad is ,the resistor pack will turn on the fan and control it's speed ,and send info back to the ecu to say what speed etc
you'd need to back probe that plug with power to the L+ and N- which is best done fan removed (because it's a pig to reach and it will probably bring the fan on ,which will eat any fingers etc anywhere near it , so be careful

re the relays , one failing will stop the fan working , as will any blown fuse in the circuit , it's not a back up relay system .

also in live data you could check fan control 1, 2 and 3 (active or inactive) radiator coolant temperature voltage and temp reading when warm etc

also also with the  codereader you can do output tests to check fan and blower motors

also also also  did you confirm that the car has NO aircon ? and never has
 I.E compressor,condenser,front rad fan not present 

[terry paget]

I was right, different socket. Here are plug and socket on the 04 car (fan now removed from car)

and here are the 08 plug and socket

There are 4 wires and pins 0n the 04, heavier wires too, only 2 wires and 3 pins on the 08.

[dave the builder]

There are 4 wires and pins 0n the 04, heavier wires too,
 only 2 wires and 3 pins on the 08.

on the 08 ,where the loom plugs in (fan speed resister ).I think you'll find 2 wires to run to the actual fan motor(this is what you put 12v to to test fan ) BUT 3 wires on the plug/car loom 

[Andy B]

have we found out what the actual oil pressure is yet? 

[dave the builder]

look at this example motor and resistor clicky
just red and a brown wire power the motor BUT the plug (which is also speed resistor ) has 3 wires

[terry paget]

have we found out what the actual oil pressure is yet? 

No, kit not arrived yet.

[terry paget]

look at this example motor and resistor clicky
just red and a brown wire power the motor BUT the plug (which is also speed resistor ) has 3 wires

Correct. Here is the 04 fan and surround, with the green resistor revealed (below the plug to motor)

[terry paget]

The coolant temperature sensor on the wet thermostat is to send temperature information to the engine ecu . the engine ecu decides IF the fan should be on and activates relays to power the plug at the bottom of the fan shroud ,
that plug is a fan speed resistor , depending on how hot then rad is ,the resistor pack will turn on the fan and control it's speed ,and send info back to the ecu to say what speed etc
you'd need to back probe that plug with power to the L+ and N- which is best done fan removed (because it's a pig to reach and it will probably bring the fan on ,which will eat any fingers etc anywhere near it , so be careful

re the relays , one failing will stop the fan working , as will any blown fuse in the circuit , it's not a back up relay system .

also in live data you could check fan control 1, 2 and 3 (active or inactive) radiator coolant temperature voltage and temp reading when warm etc

also also with the  codereader you can do output tests to check fan and blower motors

also also also  did you confirm that the car has NO aircon ? and never has
 I.E compressor,condenser,front rad fan not present 

The car has no aircon.
I tried checking control of the fan with my Chinese code and live reader.
As shown in pic, I have found the resistor behind the plug on the lead to the fan, but I do not think it controls the fan speed, that is done by the ECU. There are 2 relays shown in Haynes, one turns on the fan at a lower speed, the current going through the resistor, and the other feeds current direct to the fan motor. I reckon the resistor is located where it is to be cooled by the fan draught.
 

[dave the builder]

So ,if you know which relays do the back rad fan , bypass one at a time and see if your fan spins up  ,assume you have now tried the fan directly connected to a battery or power probe  refitted fan 
video here clicky for cars with air con but your's won't be all that different ,just no front fan and 2 relays not 3

[terry paget]

You could also simply connect the fan motor to the battery

Not so difficult after all, as I found with the 04 fan on the bench.
Applying 12 volts across pins 1 and 2 fan spins merrily up. 12v across pins 1 and 3 again fan spins up. So the fan and resistor are OK. I checked fuse 6, it was OK. I will check it again. That just leaves the relays, but they can't have both failed can they? And the ECU, and the loom.
Please advise.