I remember reading about a potential problem with moisture and the wiring harness around the firewall causing this sporadically. I'm going back some so all the details are not as clear as they once were. I think it was to do with the drains being blocked and the water shorting a plug.
I had the problem once way back after sitting for 30 minutes in 95 degrees/100% humidity waiting for my wife. I pulled in and stopped and it cleared on the restart. There was a big puddle of water where we stopped so I guess the system was over come by the condensation.

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