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Hey all, I am a Mazda Rotary guy but my sister has a MK4 that has serious electrical problems.

The engine won't start, just misfires. When ignition is on random dash lights flash on and off and the Tach does random sweeps. My guess was an ECU issue. We attempted to pull codes but the OBD2 wouldn't even connect to the computer.

We took it to the dealership who told us that the coolant temp sensor shorted out and fried the ECU. $800 per part, $3000 in labor.

I looked up the wireing diagram and the coolant sensor isnt even wired to the battery, it gets its power from the ECU so a short seems impossible. Also how do you short out a coolant sensor? It is submerged in coolant.

Any help before my sister makes a huge mistake is appreciated.
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