The battery light came on all danger red, indicating that the battery isn't charging. Hoping it was just an old battery I went to Auto Zone and had them test it. They said to get an accurate test it would have to be pulled, so I did. It's fine. Next up, alternator. I pulled it and Auto Zone tested it - also fine. To cover all bases I replaced the belt when I re-installed the alternator but of course that didn't solve the problem. The folks at Auto Zone said it's probably the wire from the alternator to the battery, and that rodents may have chewed the insulation. They recommended a local automotive electrical shop where I've had work done before. But before I pay them to diagnose it I thought I'd check here to see if there's a fuse or something I should check. Can anyone help? Thanks.
You can check if you have the battery voltage at the alternator Battery terminal at the back. If you do, you have continuity. You may have a loose ground connection somewhere.
When you turn the ignition switch to ignition ON, Do the warning lamps briefly lit and then turned off ?
Was there any service done immediately before this problem ?
No recent service. This model doesn't have a traditional battery or alternator lamp, the "Battery Charge" message is part of the Multifunction Indicator.
The battery itself measures a bit over 12 volts, and I'm seeing the same at the alternator's battery terminal. Thanks for that tip, it checks something possibly expensive off the list. The alternator and the battery both have good ground connections.
The other terminal on the alternator (I don't know the technical name, it excites the winding) is getting 6 volts with the ignition on (zero off, of course). Is that correct? Shouldn't that be 12 volts? Could this be my problem?
I don't seem to have a disconnect to the IP because I'm getting the 6 volts, but there's apparently a problem with whatever module/circuit is involved (ignition?). I'm afraid this is going to get expensive...
When I put the key in and turn it to run (switch position 2) the lights come on and stay on.
OK, One more thing to check. At the driver's side, under a lid, there is a fuse panel (where 38 pin diagnostic connector is). Check fuses 4, 7 and 10. These go to the IP.
You replaced the belt but I wonder if a worn belt tensioner is causing the problem. The alternator requires minimum rpm (its own, not engine's) to actually produce output. So if there is some slipping at idle rpm, the alternator may be shut off.
One thing you can try is to look at the voltage level at the climate control menu display ( I think it is item 24 in sensor menu) and run the engine at idle around 2500 rpm and check if the voltage level on item 24 goes up (the voltage level is about 0.5 to 0.7 V below the actual battery voltage level).
Also make sure your idler pulley is in good condition.
I took my car to a local mechanic who tested the charging system and reported the alternator was bad. This puzzled me because AutoZone tested it and said it was good. But it turned out it had a bad bearing that I couldn't hear over the engine and AutoZone didn't hear over their bench tester, so either way it needed replacing. And replacing it fixed the charging issue!
I guess the moral of the story is when you get a free alternator test at AutoZone you get what you paid for.
Not quite.
I've been trying to spread the knowledge that short alternator brushes can act in and out for pretty long time before they die permanently, so don't blame AutoZone that your alternator tested good at the time.
I've been promoting to put new VR on 100 +k miles service, but that seems to be lost in forum chatting.
When with low lights use the brushes can last past 200k miles, the above sample just confirm how much hassle can bring saving the $50 at regural maintenance service.
When I am generally against preemptive parts replacement, if anything qualify for such, the voltage regulator would be on top of the list.
Not quite. It wasn't at low rpm, the battery charge warning first appeared while driving down the road. The bad bearing was the reason why I replaced it anyway even though it supposedly tested good. Remember, the voltage from the ignition switch (the "D" terminal on the alternator) was 6 volts, which to me was suspect. I feared that replacing the alternator wouldn't fix the charging issue and that the 6 volts was the real problem. But I guess 6 volts is right.
With computerized car you can't assume anything.
I've been mounting trailer hitches and lights modules on my MB for 20 years.
Yet it took my 2008 model, when trailer light module would not turn the markers on the trailer.
Some checking later - the tail lights operate at 6V and only fog mode gives it 12V.
So when I need trailer lights, I have to turn the fogs on.
Twice, I have had intermittent opens on alternator rotors. Both times on old Delcos. They would work, but the output was low and flaky. Worse at higher RPMs when the windings would flex slightly.
It was a long time ago, but I won't forget those two soon.
Worn brushes can give a similar effect, when they are at the just-barely-making-contact stage.
As Kris says, wear items.
I've tended to swap out the alternator/starter/water pump at just under 200k on my vehicles, but I'm planning on skipping the latter two on this OM606, based on what I've read of other owners' experiences with them. The alternator, however, I've replaced prophylactically.
Any decent alternator tester can find out whether a regulator is bad by simulating the full load at a specified rpm, and check the voltage. Some even have scopes to check the diodes.
Any good technician will bench test an alternator both mechanically and electrically. Removal and checking the condition of a regulator from a stand-alone alternator will take 5 minutes, and I guess if the bearings are in bad shape, the regulator condition would be a mute point.
And 6 volts is not the right voltage for a working alternator. One of my cars in the past had no belly pan, so when I went through a deep puddle the charge light used to come on for a short while. The belt was getting wet and slipping for some time. So I installed a belly pan, the problems was solved.
I have a contrary opinion of what typical alternator testers can actually test for. The ones I've used and seen will not test under full load, not even close. None of them have had true o'scope output, though all claim to test for proper diode function. The HP required to full-load test a modern alternator exceeds the drive motor on the tester setups I've seen by at least 3x; probably 4x or 5x. My 3 HP electric motor on my homemade alternator test rig can be pulled to a standstill if I try to full-field a big alternator.
Sure, a commercial rebuilder tests at full load and prints a nice 'scope graph of RPM vs. amperes and puts it in the box, but parts stores? I don't think so.
I've never seen a test rig for alternator (solid-state) regulator testing, and I'm going to stick my neck out and say I doubt that a) most auto parts stores have one and b) they will R&R your regulator to test it.
All this is by way of saying that I'm not surprised that AutoZone's test protocol proclaimed a flaky alternator to be OK.
(Remember the good ol' days when you had to buy two "rebuilt" generators to get one that actually worked? I do, and we figured in the extra labor to R&R them twice into every repair bill. The chain store rebuilds around here were TERRIBLE. I learned how to build my own test bench early on, just to save myself the grief.)
That is why you do not get the alternator tested at Auto-zone and the like My gardener does not use an electric lawn mover either
Also there is a big difference between an alternator that is flaky and not working at all. If he had close to what is considered as a proper output voltage from the alternator, then a worn brush condition would cause a significant voltage drop when the loads (headlights, blower motor, radiator fans, defogger etc.) due to smaller contact surface of the brushes and hence higher resistance ->> reduced current output even at full field. not meeting the specs. But he had 6 volts at the D port.
Anyway, I am glad his problem is solved, hopefully for another 100Kmiles
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