Thanks Dan, can tell the dealer two others work and mine doesn't now :)

Looked at the wiring to the fan and it doesn't look like CAN bus, maybe a PWM signal, the loom goes under the battery.

Agree - The whole point of 17s versus 18s on the Mk5 GTi isn't "garish looks", it's that the ride is that much better; we test drove one on 18s, and consequently bought one with 17s. Arguably I thought the 18s looked better, but it seemed to me the suspension is clearly tuned for 17s so 18s in practical terms are a "downgrade" at extra cost purely for appearance.

And also tend to agree re: the 3 series; the wife's 320d touring also has 17s. I'd suggest 18s & 19s are well OTT for a perfectly respectable performing but in no way fast diesel estate (OK, latest 330d and 335ds are fairly fast, but not the 320d), plus the M sport rims buckle, etc etc! Admittedly 16s on an E91 touring do look too small IMHO

Tried to buy ours on 17s but none available and needed the car in a hurry so took the spec available. What tyres do you have hades?

BMWs are the same; I've never seen so much electronics inside a fan motor.

In that particular case there are three wires; power, earth and communication. The signal wire (two way signal - speed sense to ECU and demand from ECU are on the same wire) had broken internally (vibration and corrosion via water ingress), causing the a/c not to function and the ECU to log a fault code. Spliced in a new wire and away it went (and alot cheaper than a new fan, I may add),

It took a while to figure out what the signal wire did, as at the time I belived that most CAN communications work via two wires (much like I2C), whereas this one only used one, seems my education on industrial networks fell short on how single wire protocols work for two way data communication and neglected to mention that CAN can also be done over one wire (albeit at a lower communication speeds). All this for a sodding fan, I ask...why? What is wrong with a two speed fan and a relay?