2003 Protege 5 onboard computer will not communicate with scanner

[rebelteacher]

Protege 5 just died while idling and would not start afterwards. Power windows and everything worked, ignition would turn to try to start but never turned over. Had it towed to mechanic, first said it was the timing belt, then he said the onboard computer would not talk to his scanner. Sent computer off to be "reset" but computer people said they could not do anything with it. This all sounds a little hokey to me. It seems that if the computer was shot then none of the electricals would be working. The check engine light was on a day or so before this, could this be another issue beside the computer? The car has 150,000 miles and as far as I know, it has not had a tune up EVER but alas, this is my problem now and any help would be greatly appreciated!

[smokstac]

As far as I know the computer has nothing to do with whether other electronic items work or not (locks, radio, etc).

[1Mazda323Fan]

Your powertrain control module (PCM) or engine control module (ECM), whichever Mazda calls it, may have gone out, hence the dying and lack of communication. Or, the shop's scanner is dead. Doesn't explain the check engine light, though that may be unrelated. Now, after it died, did the starter turn the engine over and it just didn't catch, or did nothing happen when you turned the key? That'll help narrow down what's wrong and help us help you. Did the car make any odd noises or anything before it died? Any further info is appreciated. Also, the PCM/ECM doesn't control the windows, radio, etc. in your car. Another module handles those.

[rebelteacher]

The starter sounds like it should start but like it is out of gas. The car made no odd sounds before it died; it simply went dead and wouldn't start again. The only "strange" thing I noticed was that for a couple of months before this happened, it sounded a little bit sluggish when I would turn the key. I thought maybe the battery was getting old. We did try to restart it by boosting it off, but that didn't work. The mechanic said "it isn't firing". I don't know what that means as it does sound like it should start.

[smokstac]

You need three things to happen for an engine to start and run: spark, something to ignite, and compression...and all three must happen at the right moment otherwise you won't get power.

It used to be on old cars the fuel pumps were mechanical...meaning that if the engine was turning then the fuel pump was pumping (assuming the diaphragm inside wasn't torn). As well you had a mechanical distributor which allowed the ignition circuit to build up current and then discharge it from a single coil to the chosen spark plug...again, mostly mechanical. Finally the fuel was sitting in a big bowl on top of the engine (carburetor) and all the engine had to do was turn/move to suck in a mixture of air and gasoline vapor to be burned. Upon compression it ignited from the spark plug and you got power.

Not any longer.

Today most everything is electronic...which means in order for the engine to get both spark and fuel numerous sensors have to send feedback to the ECU regarding the position of many elements of the fuel injection system such as the throttle, cams, crankshaft, etc. If any one or more of the various sensors isn't plugged in, shorted, grounded, or has failed then you probably won't get any signal for the ECU to fire the plugs and/or open the fuel injectors and/or signal the fuel pump to turn on. Things are generally more reliable now, but, when something breaks it can throw you into a tailspin as to where to look (especially if the ECU goes bad because with that working it's impossible to know where to start).