M.O.T. Question re scavenger fan

[bonglets]

If the fan does not work would this be an mot failure?
Thanks liz

[mikeWalsall]

No ...

[haydn callow]

If it dosnt work I would fix it ASAP .... It's your last line of defence in event of lack of cooling

[Bob]

Agree with both answers.

[Simon Jones]

How do you know it's not working? It rarely comes on unless the temperature above the engine gets to 80C. The sensor is by the handbrake & you can do a quick test by unplugging the connection which should start the fan running. To test the sensor, follow these steps:

[bonglets]

Thanks for the replies. We run at about 94 to 97 most of the time and have never heard the fan come on, the ones on the radiator work though. We have the TM 2 alarm. No problem with loss of coolant, no white stuff around oil filler, starts fine, heaters work fine we only got the van in December and had the alarm fitted straight away as advised by many on this forum. It was fitted for us as per the instructions provided so presume the sensor is in the right place, temp has always shown between 94 & 97. Really worried as we are driving home from France next week and on the way down we reached 110 on a long steep incline. Fortunately we did get European breakdown cover should the worst happen.

[bonglets]

Just unplugged it and it didn't come on so it's not working.

[Simon Jones]

We run at about 94 to 97 most of the time and have never heard the fan come on, the ones on the radiator work though.

The scavenger fan sensor monitors air temp above the engine rather than coolant flowing inside it. Get a hair dryer, pull the sensor out of its mounting hole by the handbrake & give the sensor a good blast with the ignition on & see what happens. Also disconnect the wires from back of sensor & short the two wires together with something like a paperclip which should simulate the low resistance needed to trigger the fan. I may have given you a bum steer earlier about unplugging it to trigger is as that would give high resistance.

[bonglets]

Wow thank you Simon that is within our technical know how so willmgive it a try appreciate your help

[bonglets]

Tried the hairdryer test nothing happened, not happy trying to short it. We will limpmhome keeping an eye on the temp alarm with fingers crossed!

[Simon Jones]

It is safe to short it . Currently you don't know if the sensor or fan is at fault but by shorting the wires to the sensor you are bypassing it & the fan SHOULD come on. If it doesn't try spinning it by hand (ignition off) to check its not seized & then check the fuse which I think is in the fuse box under the bonnet.

[bonglets]

Thank you will check tomorrow see how we get on.

[Diplomat]

I'm a bit confused. How can unplugging the connector and shorting it both have the same effect unless the off state is represented by a particular resistance value which is neither open nor short circuit?

Frank

[Simon Jones]

It can't. See my comment above:

I may have given you a bum steer earlier about unplugging it to trigger is as that would give high resistance.

[the1andonly]

I used a 220ohm resistor as the "short" worked perfectly. The ECU reads this value and switches the scav fan on.
I believe Gasy has used a switched short to bring on the fan when towing.
I currently have a switched resistor in parallel with the sensor. 330ohm ( 3x1k in parallel) used for same purpose.