Fan comes on

[dishman]

Now look at the live data and see if you can see any odd readings off the bat.

e.g check temp readings when the car is cold, (things that basically stand out)

Unless anything stands out as really odd, you will probably then need to compare all the readings that scanner can see with established normal ones.

That's a good starting point anyway.

 

[goofy gorilla]

Well guys seems like the problem has come back..been fine since I initially posted this thread. Now the fan kicks in within 5 minutes of starting the car. Cars barely warm abd I csn hear ans see the fan running....the heaters seem normal as I drove for about 20 minutes...but noticed thst the temperature doesn't move up as before im assuming that the fan is cooling it down. Checked the water in the reservoir its barely warm.. cant be water pump as it was changed with new timing belt just over a year ago. Im thinking air lock in water system or possibly faulty sensor switches?. There are 2 switches. Are they both the same? Gonna have to drop car at local mechanics hopefully he'll tell me..

 

[Old Salt]

Post #16 suggested looking at the live data from the OBD reader. It would be a good starting point and should indicate if a faulty sensor is the cause.

 

[goofy gorilla]

Unfortunately not got the reader anymore...gonna change the sensors myself..doesn't look very difficult..think ill change the one on the side of the engine block just below the air housing...are both sensors the same?

 

[dishman]

This approach is generally a bad idea.

It really is pointless changing random sensors unless you know which is faulty, or if it is faulty.

You could actually make diagnosis more tricky as you might make something worse or replace a good quality OEM sensor with a cheaply made third party sensor.

Some sensors you really don't want to cheap-out on when replacing.

The basic wired code reader I used was £15 on Amazon. It's a useful basic tool to have anyway. So even if it sees nothing of note in the data it's useful to keep in the glove box.

As I said, look at the live data and see if anything stands out as being wrong.

For example, in my case, I could see there was an issue with my coolent temp sensor which was showing 125C on a cold engine. This was causing the car to start too lean in cold weather as the ECU thought the engine was already roasting.

If nothing obvious stands out. Look at the readings again and then find some references and compare them to see if anything is more subtly incorrect.

 

[Harry Bloomfield]

Cars barely warm abd I csn hear ans see the fan running....the heaters seem normal as I drove for about 20 minutes...but noticed thst the temperature doesn't move up as before im assuming that the fan is cooling it down. Checked the water in the reservoir its barely warm..

That suggests an issue with the cooling system thermostat, to me....

The thermostat, limits the amount of coolant, flowing from engine, to radiator. It should only open, to allow flow, if the water in the engine rises above a pre-set temperature. You should be able to let the engine tick-over, whilst feeling the top hose. The top hose should remain cold, until the engine needs to be cooled, then the thermostat should open, and you should feel the top hose quite suddenly feels hot.

Only if the coolant temperature rises even higher, are the fans run, to cool it - so that suggests a second, separate fault, of the engine temperature sensor, not working correctly. The sensor could be faulty, or the plug, or the wiring.

 

[accelerator]

My opinion - Probably a faulty coolant temperature sensor, but could be a faulty fan relay that is getting stuck.

 

[Harry Bloomfield]

Probably a faulty coolant temperature sensor

Yes.

but could be a faulty fan relay that is getting stuck.

No, the OP suggests it comes on after a bit of delay - there would be no delay if the relay was stuck on.

 

[accelerator]

No, the OP suggests it comes on after a bit of delay - there would be no delay if the relay was stuck on.

OK agreed. It would get stuck either on or off and stay that way.

 

[goofy gorilla]

Ok I just bought a obd reader will be getting it in a few dsys...will do the checks as recommended...today it drove absolutely no problems heating all good..no fan came on..weird lol probably when temperature is freezing then it happens ‍

 

[Harry Bloomfield]

Ok I just bought a obd reader will be getting it in a few dsys...will do the checks as recommended...today it drove absolutely no problems heating all good..no fan came on..weird lol probably when temperature is freezing then it happens ‍

I wonder, if the trigger for the fan, might be a thermal switch - rather than the usual sensor, feeding temperature information, to the engine management, then the engine management operating a relay.

Assuming a thermal switch, that could be faulty.