Save a Mazda 3 From Itself - Intermittent Start/Tons of Codes

So a friend of mine has a 2009 Mazda 3. The car had been nothing but reliable until recently when it started refusing to start intermittently. She had a locksmith take a look at it and his report is kind of remarkable. Things seemed to be pointing to the gauge cluster needing to be replaced, but it didn't help at all. Apparently when it does start it runs with no problems at all. I feel like there must be some way to get it fixed, but I don't know these cars very well at all and haven't found anything helpful online. What say the hive?

I'd be checking out the battery terminals making sure they're clean and that they're still tight on the posts, cheap and easy to just replace them, the main relay, and for any blown fuses. It sounds like this has to be electrical, and the intermittent no start would have me start with the battery terminals. 

In reply to mtn :

I can definitely try that, but wouldn't that affect voltage when the car is running as well?

Right before the very first time it started acting wacky, who's the last person that did anything to the car and what did he do?

Not foolproof, but you'd be surprised how often that question leads to a cause, whether it's cars, computers, or anything else.

I'd be checking all of your big grounds. Ground issues cause some real wacky E36 M3 to happen.

Yeah, I was going to say ground or terminal corrosion.

It might not hurt to reseat the fuses and relays, too.

After checking the grounds, I would check battery condition and alternator output. 
 

My Honda did strange things when the battery was going bad despite always starting. Also had an alternator that was overcharging that turned on the abs and airbag light. 

white_fly said:

In reply to mtn :

I can definitely try that, but wouldn't that affect voltage when the car is running as well?

Not necessarily. I've dealt with 2 Hondas that everything was running perfectly, nothing wrong, then with no warning we had Christmas tree lights on the dash, wouldn't start, etc. Both cases cured by new battery terminals. 

BMW are especially bad about this as well, when the battery starts getting bad or a ground is corroded the entire code book shows up