I checked the fan and yes it does work. I wondered about a previous repair because the ecu has "guarantee void if broken" seals on both sides. Since any thought of a warrantee or guarantee are long gone I took it apart anyways. I called a couple jag specialist in my area and none of them seemed eager to even touch the car one flat refused while the others said minimum $330 up front to start diagnosis. I just wish I could substitute a known good ecu. I will keep digging into the electrical schematics and try to explore other paths. Any other ideas let me know.. Thanks for all the help so far.

 

Bad solder joints often have temperature sensitivity. I suggest you use a 15-25 watt iron and fine gauge 37/63 flux core solder (available at Radio Shack) and reheat and add a bit of fresh solder to the joints on that transistor and any others that looks suspect. Heat the joint for about 5 seconds then add the solder to the joint, not the tip of the iron.

 

How does one verify that that fan is working properly? What activates it?

 

If you gently lift up the ecu you can see the fan running. As far as what activates it and at what time I have no idea. It looks like ecu doctors will test the ecu for $50 I seriously considering it. I have gone over the solders with no change I have a few other things I'm going to try and I'll get back.

 

A freind had a similar problem with XK8 98, and found that the oil level was low. Worth a quick check for a simple solution.

 

The fan runs when the ignition is turned on.