battery drain

Hi everyone,

I'm new to 12volt but not a complete newb to car electronics.

long question short.. I have found out that the CD player and the aftermarket ECU on my car are draining the battery even with the ignition off. Both are on the same fuse and the ECU was installed by the previous owner.

The car is a 93 Honda CRX and the CD player and the ECU were installed on the "back up" fuse under the hood. This started with no warning after I've owned the car for over 2 years.

What could cause them to malfunction and start draining the battery?

Thank you

An ECU that is NOT powered through a relay? (aka "Ignition" relay) And an audio system installed on the same circuit as an ECU? That's not a malfunction, that's two problems... And an amateur installation (which makes others rich - especially after a reverse-polarity battery is connected!).

There are only two things that normally go to that 7.5amp OEM fuse, the clock memory and radio constant. ECM should be fused from the main ignition, BLACK / YELLOW. Aftermarket head unit SHOULD (all reputable makes) have 2 power leads, yellow, constant input and red switched ignition. Also have your battery checked. What is it with the (lack of)knowledge and competence in NZ and Oz, Peter?

Oh Howard, you are cruel - I didn't even notice that... As you know, I stay well clear of Aussie forums. The novices are ok, but the so called experts... (LITOLs) Funny that I recently wrote of NOT oil-pressure controlling electric fuel pumps (the Aussie "expert" hackers forum response - "if it's so bad, why does everyone do it?") as well as inverter "isolation", their MEN (earth/gnd-neutral bonding), and dual-pole switching. Admittedly the latter was Chip's issue (he is still stateside and vows never to return to Oz; I did warn him - I had already defected by then), but that "anti-battery isolation" dork that proposed a Wheatstone Bridge to "monitor" parallel battery condition... Geez, that involves isolating the batteries from the load and THEN trying to ascertain what leakage currents constitute a battery problem. LOL - why not use that same load-isolation switch/relay to simply isolate the parallel battery and be done with it? Geez x ∞! But as I told Chip, that guy sold batteries. I rest my case! Unfortunately rip-off merchants are rife down here, and there are plenty of gullible customers. Dusting of my still-bad memories and getting back to the OP, I'd assume the Honda is like most Jap cars and uses an IGN+12V controlled relay (with series diode to its coil to prevent actuation if battery connections are reversed) to power the ECU. (Usually dual SPST relays are used - one pole for the ECU, the other for injectors etc.) You'd think that someone installing an aftermarket ECU would be clever enough to use else imitate the original ECU's power circuit, but hey, we only just got off riding kangaroos to work. [I wonder if it's one of those "multi-map" ECUs that still seem so popular down here - they have up to 32 different maps you know; all you have to do is chose the right one (after dyno-tuning them all, of course!). Ooops - post-traumatic flashbacks again.] Thanks for suggesting the battery. I decided to be short and sweet. I suspect nothing has changed with the OP's car, it's just that it's now an aged battery. And it's probably pre-aged thanks to that constant drain. Aussie forums will probably advise he just replace the battery, then they can sell him another in the one next year or 2. Boy I'm narky tonite. Maybe I should get some sleep later instead of making it two night's straight? I am cruel. Just because we get 6-8 years from our cheap batteries, only spend $15 on automated battery isolators, and do out-performing stuff for a pittance... Maybe I can sell a cap to increase the OP's battery capacity?

Ha, very funny a cap, and pray tell Peter what law of thermodynamics will that break? Some one's got to fall for it. Every insult intended, my daughter is about to become a Kiwi, I've already warned her off Ford Anglias, Morris Oxfords and Japanese/Korean stuff that Oz doesn't want. Oh and 10 year old episodes of Corrie. The Brits generally try to be know-it-alls and fail miserably by the way.

The i'th Law.    [Yes, that is a complex law, known by electricians as the j'th law {not to be confused the the J-Law or J-Lo or its/her curve(s)} and by geometricians and cartesianists as the 90-degree or π/2-radian law, namely that fixed objects cannot be moved, and, if slow enough, is as good as rested or stationary {which is backwards to some}.] And sakii987, I else we can help. Don't let my bitchin' get to you. Incidentally, where downunder are you? (Just in case you are nearby. After all, it's not such a big place - though as many know, it is bigger than its neighbouring Switzerland - the home of Molly Humdrum's ABBA. And we know Australia has more snow than Switzerland.) You may have realised that if I'm not bitchin', I'm joking. Else rambling.

No dear boy, Abba = Swedish which thus automatically makes Sweden the most boring country in Europe, beating out Belgium and Holland by a narrow margin. You do realise that I've now managed to insult both your place of birth and your mum's? Or was that Nokia home to Finland, or is it the other way round?

Hahahah, nah I wont let the bitching get to me, i can take a joke :) Im in sydney, near liverpool.. close to you?

back to the problem, i agree the installation is amateur, but I'd say whoever installed it didn't care about possible future problems. I checked the wires around the ECU and they were soldered, but wasnt a great job. Howie, you're right about the fuse, it should have only been for the radio constant and the clock memory, but they decided they will put more things on it as well (at least the fuse was upgraded!).

The battery is drained as long as the ECU is connected. Same problem was with the CD player, now its out. I will go and have it professionally checked to see whether the drain is significant enough to drain the battery, but it is weak now, after being discharged a few times.

Do you guys know of anything that could cause the CD player and ECU to drain the battery even with the ignition off? I want to try and find the problem, if there is one, rather than change the battery, CD player and ECU and have them do the same..

Oh and the ECU is Microtech MT8. It was all working fine, till that one day.. and i can't remember of anything that happened that could have caused this either.

As I said, I'll have it double checked by a pro (and lets hope it is a pro- got bad experience with mechanics) and hopefully just a new battery is all I need (have a feeling they will suggest this...)

If you guys know of anything that could cause this, it would be of great help, otherwise, I better hope i find a good auto electrician :)

In the other think about Oz morons is you you don't effing listen! Peter and myself have in great lengths already gone in to what should be wired to where and how.

I know that its not perfectly wired, the fact that its going through a fuse with a few other things says it all.. For installation manual, the manufacrurer's website provides that.. The thing is that no matter how it's wired, it still works!

And it has worked perfecty.. now it just drains the battery.. I certainly dont want to re-wire the whole thing!

My question was simple.. and it still hasnt been answered.. :(

N ps i do listen, but as i said, i dont want to rewire it.. Just want to find out what caused it to start draining the battery, as it didnt use to.. i dont want to waste my money and replace it and have thye same problem again...