Hi, having another issue with my rx8... theft system acted up a few days ago and wouldn't let me start the car. after disconnecting and re connecting the battery a few times waiting half hour inbetween there is 0 power now. At first i had a solid car with key in it light on which is the immobilizer system. But as soon as i pressed the brake pedal or turned the key it would cut out. After a couple battery resets i now dont have that light on either. No horn no headlights no nothing. I have checked the battery and its at 12.6v, but what confuses me is when i probe the connections to the fuse bos i only get 10.6v. with key off it should get the full 12v correct? I have also tested resistance and it came up 0. all fuses including 120v main have been checked and are good but i cant figure out why there is a huge volt drop from battery to fuse box. Also fogot to mention i resistance checked wires from battery to fuse box and they are good aswell. kinda at a loss here.

 

Sounds like a dead battery or very poor battery terminals. It may show voltage but not actually have any current capacity left so pushing the brake and turning on the brake lights brings the whole thing down. 10.6V at the fuse box without load probably drops to 9 when there is a load.

 

Ok quick update. After testing from battery terminal cables to fuse box. And from battery terminal cables to alternator I get 0.000 resistance. However after 5 seconds I hear a jolt noise and resistance climbs to 300+ then hits OL. This was with battery disconnected. Also just tested with battery connected. Fuse bos is getting 0.000 resistance. Battery negative to alternator is getting 0.000. but battery +to alternator goes instant OL. I'm assuming the issue may lie in there? Guessing I should check harness going down to starter motor too since it's all tied together.

 

I'm not sure I'd expect battery to alternator to be continuous with everything off. There's a vreg in the middle, which probably includes a diode. You might find its continuous if you flip the multimeter leads around, but all the same, that by itself doesn't sound alarming. In general battery+ should be open loop to everything but lights and immobilizer with the key in OFF.

The jolt noise is interesting though. Sounds like a relay or some kind of ground fault protection? You're shorting battery to all kinds of things there so be careful. Someone already fried their ECU that way.

When you say you have no power, what about dome light or dash 'welcome' lighting? I'm thinking of small loads that still run at 10.6V. If I saw 12V at the battery but 10.6V downstream I would check that the terminals are clean and snug. Easy thing to try/eliminate before going down the rabbit hole.

Check for phantom currents at the same time. With everything off the car should draw 0.01amp (it'll spike to 0.2 or so when you first connect the meter, but settle quickly). To test this connect the battery+ battery terminal but use the ammeter to bridge battery- post to battery- terminal. If you find its drawing more that might account for your voltage drop.

 

Ah ok. I can re test everything with the key in the on position. But I assumed that wouldn't do anything as I don't have power to anything.

 

ok just got home from work today. went out reconnected battery. before i could put the key in it had power again somehow. then i put the key in clutch in tried to start it and as soon as i cranked all power cut again. now its back to being dead. i did check voltage after with key in and on to alternator was .060v. resistance from batt to alt was good also from bat to fuse box good and from fuse box to alt good. I still feel like this is due to the immobilizer system but i thought that there should still be power to the horn and lights? thats where im stumped.

 

Did you confirm the battery is good? It sounds like it drops voltage as soon as you put any load on it, soo...

 

well update. problem solved was about to pull battery harness out of car to check for shorts or burnt wires. but my positive terminal was bent a bit and had a friend say to try replace them first. did that 10 bucks later its running again. So i guess moral of the story, even with voltage, even with no resistance, if your terminals arent near perfect. electrical fuckery can and will happen i guess.

 

Here's the culprit. Still intact and I even cleaned the inner part. But with a bend like that I guess it's time to swap it.