Sorry if this is lengthy, but I want to give a clear picture of the issue.
As stated in my topic heading, I've joined the forums owing to a car problem that our mechanic couldn't diagnose. I have a base model (no keyless entry) 2.0 liter Mazda 3, about 135,000 miles, not driven hard or raced. Strictly commuter.
Drove it yesterday afternoon to pick my kid up from school. Car ran just fine. Got my kid in the car, put my key in the ignition, and nothing. No crank. No electrics. No instrument panel. No security light. Zilch. Called my fiance and he drives over from work to help. We are sitting in my car discussing what action to take when the instrument panel starts doing the same thing as the panel in this video:
(Not my video! NSFW language warning for some swearing.)
After seeing that weirdness, we tried turning the key, but again, no crank, no panel lights, nothing.
Fiance hooks up jumper cables from his car to mine, runs engine for a minute, my car starts right up. We replaced the battery a month ago, so we decide to go down the road and get it tested to see if it's faulty. After unhooking the jumper cables, I do a few laps in the parking lot bc I have a sneaking suspicion it might die again. As I'm driving, the dials start going wild again, "Welcome" message on clock display flashing along with welcome chime, power steering cutting out and in. It does that about three times, then loses power and dies.
We hook the jumper cables up again and run his car for about 20 minutes. I try the engine again and the panel lights up, but beyond that all that happens is the starter cranks. We wait a little longer with the jumper cables running and try again. The engine starts okay this time. We unhook the cables and try to leave, but as soon as I shift into drive, the car dies again. No electrics, no brakes, nothing. Coasted into a parking space and pulled the e-brake.
We took the battery out and had it tested. Battery was fine. Had car towed to shop. Starter is fine. Alternator is fine. Battery is (again) fine. No codes thrown. Fuses are all fine.
The shop got the car to start this morning and they drove it around with zero issues. The mechanic is stumped. Thinks it might be the "ECU"? They said to take it to a Mazda dealer, but the only one in town is *not* honest. I've had big problems with them before and don't trust them to be straight about what's going on.
Any ideas? Is it the computer? Loose wiring? I'm afraid to drive it until this gets sorted out. Don't want to lose my brakes and power steering without warning!
Thanks much for any input!