Before I start mucking around with the car, its an EL fairmont, used to be auto now manual, recently the temp gauge has been going to maximum within 5 seconds of starting the car cold, and the thermofans running at full speed. It would be like this once every 3 cold starts, for anywhere from 2 seconds to 2 minutes. Only from cold though. Its making my job of diagnosing the fault a little harder.

I recall if you didn't do the resistor mod after pulling the auto out, the thermos would run at full speed. What I dont recall is does the temp gauge also go to maximum?

If not, it'll probably be the engine temp sender.
If so it could be the resistor or a wire has broken that I added.

???

It means the cluster is not getting temperature information from the ECU.

And since the thermo fans are going straight on high, it means the ECU may not be getting temperature information from the sensor. The ECU assumes the engine is hot and runs maximum cooling.

Id say check the wiring and the sensor itself. You may have damaged another wire when you did the resistor mod.

thanks for the reply arm79,

however I didn't add, when I unplug the engine temp sensor, the same thing happens - thermos full speed, dashboard temp gauge maximum and the warning beeps go off.

So does the auto temp sensor do exactly the same thing? If so I'll replace the resistor, reason I'm asking first is I've neatly integrated the parts into the loom and cut off the auto wiring since I dont need unnecessary wires and its a bit of a PITA since its all neatly wrapped up and stuff.

If the auto trans sensor in the ECU is not correctly tricked, it will cause the thermos to go on high. But wont cause the dash gauge to go high. Get your multimetre out and measure the voltage across the trans temp pins and see if its in 'normal' range. This will tell you if its the trans temp causing the fans to run high.

If you pull the coolant temp sensor when the engine is running, then the ECU is doing the right thing. It sees no temp signal, so assumes overheat, and runs fans full and the gauge goes all the way up. Also put the multimetre across the coolant temp sensor pins on the ECU when the car is cold to see if the ECU is seeing a voltage. If it isn't, its something in this wiring causing the problem.

I can only assume there is a broken or damaged wire somewhere before the ECU.

Thats what I needed to hear - the trans temp sender cannot make the dashboard gauge go to maximum. It's likely to be the sender, wiggling the wires does not make any difference while the fault exists.

Cheers