Charging System Tests

What is your diagnostic procedure when you suspect the system isn't charging or you want to rule out battery or alternator?

It seems like the last two times I got my butt kicked they were both charging system issues. One of them is in my bay now and I want to get it out in the morning!

I'll start a repair thread on that one in a min

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Sorry I missed out on your Express, sir. Glad to see it got fixed! Bad parts happen to good techs.

I'd thought about doing an alternator testing sticky at one point, but it's so tough to generalize with all the various systems out there today. :silly: Internally regulated systems are pretty straightforward. But, even then there are variables, like Honda's low charge rate setup.

I can tell you that a lot of it comes down to product knowledge. Scan data can be extremely helpful, but only if you're halfway familiar with it. If you have a scanner handy, I suggest picking out some known good vehicles and getting familiar with their charging PIDs. I can provide some basic theory and known good data if you're interested.

As far as ruling out a battery - if I genuinely suspect the battery is the source of a system problem, I'll just swap it with one off the shelf. :lol: Or rig a jumper pack in.

I dunno if I answered any of your questions? :blush:

Known good data is ALWAYS useful. I'm always interested in that. Basic theory is always good for a refresher as well

Yes, that was helpful. I will look at some pids on different designs.

I guess I'm just running into how to interpret some of the data. For example, the express van. Engine running, the L terminal read 14.4v when the spec was like 2-11v. I didn't know what to make of that. Also, with the hz being 130 instead of 200.



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Tutti57 wrote: I guess I'm just running into how to interpret some of the data. For example, the express van. Engine running, the L terminal read 14.4v when the spec was like 2-11v. I didn't know what to make of that. Also, with the hz being 130 instead of 200.

Where did you get the 2-11V spec? That sounds like a reasonable value for an RVC system (variable charge rate based on loads/temp/whatever), because those systems pulse the L terminal voltage to command a varying charge rate.

But, I believe your Express is just a good ol' internally regulated system. :lol: The L terminal voltage goes high (the 14V you saw) to command charging, and the alternator figures it out from there. When the alternator fails internally, it grounds the L terminal to signal a problem. The F terminal is just a feedback about how hard the alternator is working.

Someone correct me if I've got it backwards. :silly:

EDIT: Went back and read your other thread. You saw the 14V reading on the brown wire, which is the F terminal, not L. My bad!

A steady reading of 14V on that wire is either 100% or 0% duty cycle, I can't remember which. :silly: This Remy bulletin explains it better than I can:

Yes so many different systems that are so over complex, the method for testing Ford alternators is at least simple and well documented
I have tried to get my head Honda system and can't see an easy way to test it other than by-passing it.
On BMW the IBS failure at least is easy to diagnose.

The only solid rule is you need to get a handle on the battery condition and charge level before testing, the charge level especially with modern batteries that often are difficult or impossible to get to accept a recharge if completely drained.

Andy.MacFadyen wrote: On BMW the IBS failure at least is easy to diagnose.

I've never heard of this. :blink: Tell me more, please!

Tyler, thanks for posting the remy link it'll be a handy quick reference in a pinch.

Basically is a smart battery earth cable with a microprocessor that monitors not only battery voltage but the current going in and out and the battery temperature. Unlike the Honda charging system which is an economy & emissions the BMW system is aimed at extending the life of the battery by estimating state of charge and battery health. The IBS processor frequently fails usually due to water ingress. Problem usually shows as parasitic drain. BMW have revised the part several times, often the module is simply disconnected to fix the issue, many guys on the BMW forums disconnect or completely remove the IBS while the system and battery is still healthy to avoid future problems,

bimmerscan.com/bmw-intelligent-battery-sensor-ibs/
Keith Di Fazio has a good YouTube video on one

We actually might be dealing with this exact issue out our shop with a 525. Having a heck of a time finding the draw. Pulled every fuse we could find on the things with no change on a 6 amp draw.

I believe the tech working on it did get it to drop after unplugging the dme. He also noticed a buzzing sound near the throttle body.

Worth looking into!

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Yep, that was it!

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6 amps!

It really dosen't take much to stop the modules on a BMW from going into sleep mode -- they are a pita to find parasitic drains on.