Hi,
I have been having some very serious and confusing problems causing my 2005 Mazda 3s sedan (automatic) to not be able to start the engine. What happened was that a couple months ago, on a hot day, I had been driving for a few hours (I work as a delivery driver) and when I had changed direction to go forward after one stop, all power to the car went out completely (lights, engine, horn, etc.) but that came on again by itself about 3 minutes later before I even had a chance to open the hood. A little later as I was driving, it started to happen again but didn't go off completely. However, about 1/2 hour later, it did, I think just as I was starting to back up. This time I could not get it to come back, even with jumpstarting. I had it towed home, and the next day as I was cleaning the battery terminals, accidentaly connected the two + cable wires together without the washer inbetween, which apparently made a better connection. The power was back on to the car, but the engine would not start. The immobilizer light shows code 16 (instrument cluster can't communicate with PCU) and I cant read the OBD codes like I used to be able to. There is no cranking, and I eventually found that the problem is that the main relay is not closed by the PCU as it should be when the key is turned ON, keeping the engine fuses and ignition from receiving any power. I checked all the fuses in both fuse compartments, and all the relays with a small battery. They all work, but the computer for some reason does not allow the engine to crank. I tried reprograming the keys (although the battery had been disconnected for a long time several times before without any problem) and although it went through the programming sequence properly, it still won't start. We also replaced the started even though I was sure that wasn't it. I found a few little almost broken grounds near the headlight, but even with these connected up there's still nothing. I did some testing of various wires also as directed by mechanics, but I didn't really find anything wrong except there does seem to be missing voltage on a couple of the wires to the PCU. I'm not very good with electric charts, and so I was wondering if anyone can guide me through exactly which wires in the harness to test for voltage to determine if it's just that a surge when the battery cables disconnected from each other erased the memory, or if the whole pcu is broken, or a short or something else. If you go to the dealers they try to replace the instrument cluster, PCU, wiring harness and more for thousands of $$ when it could be just one simple wire. There is a thread on a different forum that gives more info, but they weren't able to help more with testing. Total Electrical Failure - Mazda3 Forums : The #1 Mazda 3 Forum
Any further help would really be appreciated if you know what to test to determine exactly what the electrical probelm is. I'm able to provide wiring diagrams and or pictures of the car if needed, since I really need to get this fixed as soon as possible without spending huge amounts of money.

Eric

 

I finally got it fixed after more than 2 months!! All that apparently was wrong was that the fuse box plug was pushed up slightly by pieces of pine tree seeds or something that I forgot to clean when I had disconnected it! I'm so glad to be able to finally use her again, but now unfortunately the headlights and dome lights flash like a police car when off (but not when you turn them on) but I'm sure I'll be able to fix that, and it might have something to do with the alligator clips I was using as ground wires that I haven't properly fixed yet