ASAP No Electrical Power to Car!
 

UPDATE: Some problems fixed as car now starts. Does not idle or rev. Please see POST #49 as that is beginning of persisting problems. An update on POST #68, Page 3 updates these new problems, but Post 49-68 explain them and there is a VIDEO LINK to how the car is running. Thanks!


Hey guys I need some help QUICKLY if you don't mind,

I was going to be getting the car going today as I travelled 900KM to get it, but I have run into something very unexpected:

We put the booster on the car, left it to charge on high at first. But the horn came on, the parking lights came on, and it does not sound like the alarm as the horn is simply full blast, no 'beep beep' like normal. I cannot get this to turn off.

BUT, the main problem is that I have NO power inside the car - No interior lights, dash lights, nothing. The headlights seem to work, and when I turn the key you can HEAR something, but there is NO power.

I need to figure this out FAST as I need this car running today, any help is extremely appreciated!!

Essentially, the horn is stuck full blast on but there is no power to anything else in the car, yet I can turn the headlights on. Not sure where to start, but this needs to be figured out quickly, it has been sitting for a few months, but battery was on charger for several hours

(Edit: If you are reading through now, I have since realized that there isn't a BCM on the RX-8, so any reference I make to it is incorrect / flawed)

Did you have the battery connected to the car while it was on the charger? Sounds like you did and the charger fried electronics. Probably the BCM (Body Control Module), possibly more than that.

STart checking every fuse you can to see if the no=power inside the car is from blown fuses, then move on to relays. The constant on power for some stuff has to mean that something shorted out and is not being caught by a fuse. Could be a relay, but is more probably one or more circuit boards.

It was charging on low for some hours but yes was connected. So would that explain the horn being permanently stuck on?

Okay apprentely my dad said it was charging on low overnight but he had the positive cable off

It could.

I admit I'm taking guesses here, but forced electrical current through the car isn't ever a good thing. Trickle chargers have warnings about not charging while the battery is connected to the car.

You almost certainly blew one or more fuses or relays, the horn stuck on means something in the horn's circuit is shorted out and not being caught by a fuse, so that might be a melted relay. Unfortunately, the most fragile part of the car electrically is always whatever circuit boards are in-line with the current. They melt and just about anything can happen. Considering everything you are mentioning has to do with the body control module, that's where I'm first pointing a finger at.

Just positive off and not negative can be just as bad. Always disconnect negative before positive, and always reconnect positive before negative. This advice precludes the possibility of leaving the positive disconnected but the negative connected.

You might not have these problems from the charger then, but from the disconnect and/or reconnect of the positive with the negative still in place.

Is there any way of checking the BCM? Like could it be that and other boards? I'm fine with getting a used one and swapping it in if that's possible

M A Z D A

Body and Accessories, there is a BCM testing/inspection section.

Thanks a lot, that is where I will start. I had just pulled the PCM out lol

I am looking at this:

http://foxed.ca/rx7manual/2003mazdar..._S01_0816.html

And have looked through most of the external links, but cannot find BCM anywhere? Unless it is referred to differently

Um, looking. Mazda does call it the BCM, but they call it a few other things. I have a bit of an advantage in that I work for a company that takes all OEM documentation and makes it easy to read, search, etc... so I actually found it through our own site. Needs a subscription to view though so I can't just link you there.

Also, is it possible that the PCM or any of the components by the battery box got fried? I am still trying to figure out where the BCM is... my plan is to see if there is voltage going to it. If there is, then it's probably fried. If not, then maybe a wiring issue?

Ah, okay. I'm not sure that the BCM is replaceable on its own, I cannot seem to find anything for sale online relating to it. Like I have in my previous post, I removed the PCM, but someone locally said I should buy a new wiring harness with the fuse box?

I just want to find what I need to and replace it... I only wish I knew more about what I was looking at :wallbash:

Another thing to mention, I tried hooking up a scanner (physical and Bluetooth) to the OBD2 port, got no power out of it

Still hunting for what you need, might have to copy and paste it, even though it's huge.

Have you checked every fuse and relay in both fuse boxes?

By both fuse boxes, I assume you mean the inside the car and the one under the hood? The one inside the car is fine, and all the fuses on the outside are fine as well. I am currently testing relays.

Oddly enough, the Horn relay seems fine, as is it's corresponding fuse. I even put a different relay in, and the horn is still continuously on, which seems odd

Ok, so it is only referred to as the PCM. I am just getting my Mazda's mixed up.

The inspection article is: Engine -> Control System -> PCM inspection.

PM your email address for something else useful that I can't post here.

Forgot something important! My dad had gone and opened the hood this morning, which means he went in the car and what not. When I went to go in the car, I unlocked it with the key (never knew it was unlocked), and that is when the horn went off... not sure if this makes a difference.

Yeah, if all of those are fine, it's probably a circuit board :sad:

Note, that swapping in another PCM isn't quite a plug and play. You will need to reset stuff. See Ash's thread here: https://www.rx8club.com/tech-garage-...1/#post4409733

Hmm... interesting. Not sure what that means just yet. Was this done with the charger connected?

Well that's kind of unknown. Like I said, could have been timing, because as he was getting the charger on, I opened the door. But we aren't sure which happened first unfortunately. Regardless, even now with just the battery in, the horn is stuck on yet the fuse and relay for it are fine

Assuming that this procedure is not something that I would be able to perform? That would suck, as the nearest dealership is well over an hour away

If the BCM is screwed, why would the headlight function in the car still work? This is confusing the hell out of me

Yes, unfortunate the reset is with dealer software. I do not know the consequences of not following it to know if it's something that you can ignore just to see if the board is bad.

The process is very long for the PCM inspection, but it's probably your best bet at confirming or disproving a PCM failure.


Edit: Hmm, the PCM inspection process has very little to do with the interior of the car. What I sent you in email has a chart near the beginning that shows the relationship between the various modules. I'd think that it has to be involved somehow.

I really don't want to panic you into the wrong conclusion. I've never dealt with this directly so take what I say with a grain of salt.

The headlights are just powered via a relay I believe, simple circuitry, does not depend on the PCM.

Yeah it looks like it will take a while, but whatever has to get done does. By what you are saying, the PCM may be fine, but the BCM not?

Do you think it would be best to just haul it to the dealer at this point? Unfortunately I am not sure what use I will be after testing the relays and even PCM. I would like to be able to test and fix myself, but all this information has gotten me to the point where I don't even know where to begin after relay testing. Probably get charged out the ass for the work though at a dealership...

Makes sense, never even thought about that