Looks like I have a project this weekend. Just bought a new battery 2 days ago because I thought my other one had bit the dust. Well now my new battery is dead. Have to figure out what is drawing my battery down so I went to Auto zone and had them check the alternator while it was in the car running. The scanner came back as a bad diode and to bench test the alternator. While it was running the testing cycle, it caused the engine to shut off. I can turn wrenches pretty well, but I'm not an electrical person. Is the diode something I can change without taking the alternator out? If so where can I find it?

 

Pull the alternator, have it bench tested. If it's the regulator, that can be replaced by you for about $15. If not...there are alot of places that can rebuild it for about 50 to 60$$. If you want a new one, make sure you get an exact match. Make sure before you get it home it has the correct pulley setup as your original. If the test killed the engine completely, it is running strictly off the battery.

 

Let me know the fix. I have the same problem. I put a disconnect on my terminal because I rare drive, but I definitely want to fix it.

 

I have to figure mine out, it is my daily driver.

 

I've made my living troubleshooting electronic (radio, radar, siren, microcontrollers) for 34 years and I can tell you that what you posted makes little sense. If what they were doing really made the engine die, they were doing something pitifully wrong.

It IS possible that the alternator has a shorted diode, and that would drain the battery somewhat quickly. But the diodes are not part of the regulator - if this is the issue, get a new alternator and be done with it. Here near Atlanta, I bought my SE a new Valeo alternator for $199, took three hours to wrestle the old one off and put the new one on (with time to run to the store in between).

When the rebuilt one died, I had it replaced in an hour.

Now, if you really want to find out what is draining the battery, there is one way:

1. With the car off, doors and trunk lid closed, disconnect the negative battery cable.
2. Insert a digital meter set to measure current in series with the battery negative post and the battery cable.
3. Current of up to 1/2 amp will flow, wait 90to 120 seconds for all the modules in the car to initialize and then hibernate; the current will do down.
4. After two or more minutes, if you see any current over 55mA (or .055 amp), you have a problem.

If you see too much current, remove one of the 50 amp fuses in the little box next to the battery. If the current does not go away, remove the other 50 amp fuse. (One feeds the engine fan module and one feeds the antilock system). If you still have current, remove the 200 amp fuse.


If you STILL have current, it is almost 100% certain the alternator is doing it. If removing the three fuses makes the current go to zero (and it should) then put the 200 amp one in and start pulling fuses in the box on the driver's side of the engine compartment.



I suspect you have a lot of current, on the order of several amps, in order ot kill your battery as fast as it is happening, so this should be easy to find, and not TOO hard to fix, depending on what it is.

 

Thank you for breaking it down in terms I can understand. I'll update what my findings are.

 

P.S. for mine it takes 3-5 days to drain if I drive daily it's fine. Free advice appreciated.. already put New battery in. Same problem.

 

On a Delco alternator you need to disassemble the alternator to change a diode, suspect the Crossie is the same. No big. May be a rebuild kit for it, might check eBay


Driven daily fine, leave for a few days sounds like a drain somewhere. Spec is under 50ma with everything shut down.

 

See post 5.

You can screw around all you want to - there is one way and only one way to know what is going on - put a meter in series with the battery ground cable and see what you have.
There is actually a good Youtube video on how to do exactly what I'm saying - but I can't find the damn thing now....

 

Agree with both your posts Pizza with one exception, a 200ma drain (.2A) will kill a battery in less than a week. Mine usually run 20-30ma. 50 ma is just the spec and have left for two weeks once.

 

I’ve been out of the service business for 20 years but we used to put a load on batteries with a VAT machine and see if the alternator output picked up to compensate for the load. If the alternator has no output the load on the battery would kill the engine. I may be a dinosaur however.

 

Agreed. I was taking this "bad diode" too literally.

Certainly, if system voltage sagged enough, even the coils in the RCM will loose enough energy that, even if the injectors, ECM and other stuff managed to keep going, the engine control relay (and others in the car) would release and the car engine would stall.

 

My experience is that most systems are designed to run as low as 9V but internal and dash are liable to be a volt lower than the battery. Also the alternator DC is very noisy and usually the battery acts as a big capacitor to filter it. If the battery is bad, the alternator could be putting a lot of noise into the system but the real way to tell is with an o' scope. (Meter on AC may show something).

 

OK, update on results. No battery draw. Pulled the alternator and had it bench tested, all good. Turns out the new battery was bad out of the box. Took it to advance and they tested it at 12.5 volts and 120 amps. Replaced it and all is good.

 

i had to replace a battery on my previous car and went to advanced. they have 3 levels of "quality" in their battery line like many manufactures do. i wanted the platinum (or whatever the top of the line was called) but they didn't have one to properly fit the vehicle i needed it for. they did have the mid grade however and i started a conversation with the "tech" who came out to do the replacement. since i couldn't get the top of their line i was a bit concerned about quality. i was told that the lower level battery experienced an approximate failure rate right out of the box (so to speak) of almost 50%. the mid range battery failure rate was approximately 30% out of the box and their top of the line product failed approximately 10%. like many things these days, quality control is minimal if it exists at all, and they would rather replace a bad item leaving the quality control to the end user, than to pay for it at point of manufacture.