I've had my 1996 3.2 xj6 for three months or so and all the time I was using the climate control to warm me up the car has been faultless. Since the weather has changed and I'm using the climate control to cool me down the car has developed a fault.

Basically, the car is fine first thing in the morning when it's cool. It starts on the button and you can drive around, start and stop the engine with no issues. As soon as it's parked in the sun for a couple of hours and the interior gets hot the engine won't crank, no indicators, wipers, interior light, no headlights - no power getting to the body processor unit.

Wait until morning and it's all back to normal - until the sun gets working. I know it sounds bizaar, but it's true. The day before yesterday was cool overcast and rainy. I drove the car in the morning, parked it up and drove it in the afternoon - I checked every hour or so that the interior light worked when I opened the door and it was all fine. Yesterday the sky was clear. First thing the car started, I checked through out the morning every hour or so - just opening the door to see if the red marker lights were working - no problems, until midday, the sun was up, the interior had heated up and no interior lights, no crank, etc etc. I took the BPU out and there's no power getting to it.

On the BPU power plug the brown wire with the black trace made my volt meter react very slightly.

The only thing I could think of was the solar sensor - maybe that was causing a short or something, so I covered it and everything was fine - unfortunately that was the overcast day. Yesterday morning I disconected the Solar Sensor, and that afternoon, in the sun, the same old BPU problem.

Please help - one of geniuses will know what's going on. By the way, the BPU in my 1996 car is dated July 2009 - so there have been problems before. I bought another BPU from a 96 car and swapping them over makes no difference so I don't think it's the unit, I think it's the power to the unit.

Can I shortcut all the diagnostic side of things by just running a fresh power wire to the BPU?

Many thanks.

 

I'll take the deafening silence as a "don't know" then.

The car is now fixed - thanks for your help.

 

what is it that the solar sensor really does anyways