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Charging system issues and fixes

Monday, April 2, 2018 - 07:00
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Bad batteries causing problems is nothing new, but what is relatively new is the extremely strict adherence to manufacturer specifications. It’s essential to understanding that the small fluctuations that were acceptable even a few years ago can now cause major problems and can indicate where the problem lies. Keeping this in mind while taking measurements for diagnosis is critical because, as one excellent tech recently told me, “Close enough actually isn’t.” 

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Another important thing to be aware of is that many manufacturers use one-way clutches and pulleys on many of their alternators, and not checking for this can result in an embarrassing and costly come-back.  

The one-way clutches are used for various reasons, notably so that the serpentine belt needs less tension and is therefore easier on everything in the system that is driven by the belt (or drives the belt), and also so that there are fewer noises and vibrations from the system. This is indeed quite a difference from the days of getting as much tension on a belt as possible to eliminate noisy chirps under high load (I remember techs using shims under the A/C compressor mounts of a 2000-era GMC truck used for racing to raise the pulley up slightly, increase tension on the belt, and thus get rid of a brief squealing noise at very high rpm). 

Four things to check before replacing an alternator

1. Verify all batteries in the system are OK — fully charged and capable of accepting and delivering a charge.

2. Check if the alternator uses a one-way pulley.

3. Verify that the control module isn't directing the alternator to shed loads or reduce output.

4. Verify that the cables, connections and fuses are all OK.

It’s certainly easy enough to check if an alternator pulley has a one-way clutch or not – with the belt off, check if the pulley rotates freely in one direction but not the other. Not hard at all. 

However, if you’re still unsure, check service information and find out because it’s important to verify that the replacement part being used also has a one-way clutch installed, and not just to prevent noise and vibration, but also to prevent the vehicle from coming back with the charging light on. 

This is important to do even if the replacement part came from the dealer and is handed to you still sealed in the box. 

One dealer tech I worked with was in a rush on a Saturday morning, and he didn’t check. He just installed the component the parts department handed to him and sure enough the replacement part didn’t have the one-way clutch on the pulley (even though it looked the same and fit perfectly). 

The vehicle road tested OK, and the customer drove away, but unfortunately the vehicle returned less than a week later with the charging system light on. And this particular alternator was downright ugly to replace once, let alone twice – it was way down in the engine compartment and underneath everything, and the engine had to be raised and various components removed to access it. However, difficult as it was to get the alternator on and off, installing an alternator with the clutch in the pulley did indeed fix the problem. (And of course, ensuring that the spacer bushing was pushed back enough so that the new alternator easily fit on to the mount made it a bit easier, though it still wasn’t a fun task at all.) 

The sealed pulley on this Toyota alternator indicates that a one-way clutch is used in the system, and the replacement part needs to also have this clutch to prevent problems.

And if you’re thinking you could just quickly swap over the pulleys if you’re faced with this problem, think again. Removing the pulley is not just a matter of undoing the nut, popping it off and then removing and swapping it out. Pulley removal and installation requires a special tool and is not a simple task at all – trying to do it isn’t recommended. Perhaps save a headache by ensuring that the replacement pulley is the correct style and size and that the one-way clutch on the new unit is indeed operating correctly before installing it (if you’re not sure, check service information and find out for sure). If the pulley isn’t correct, think twice before installing it anyway – the one-way clutch is important and leaving it out is not a good choice. 

Finally, it’s not uncommon to re-use the belt after replacing the alternator, but it is important to note the direction of rotation and reinstall the belt so that it continues to rotate in that same direction to prevent underhood chirps and other noises from developing. Never use belt dressing or the like to eliminate a noise as it can ruin the belt and make a mess on every pulley in the system. A little bit of care can prevent problems from developing and returning. 

Checking pulley condition has always been a good idea, especially if there’s belt noise, but now there’s just a bit more to inspect — that the one-way clutch is working OK and that the replacement unit does indeed come with the clutch installed — and that it works. All quite simple once you get in the habit. 

ECM control 

Finally, since the alternator’s output is so carefully monitored and controlled, it’s also critical to ensure that the control module isn’t reducing alternator output for any reason and that the actual connections, cables, fuses and connectors are in excellent condition before replacing the component – it doesn’t take much to cause a problem, and alternators are often wrongly accused of failing when the actual problem is in the control system.  

Even a fraction of a volt or a tiny bit of resistance makes a big difference on newer vehicles and shouldn’t be dismissed as “close enough.” Those tiny variations that were acceptable before are now the difference between the system working correctly and malfunctioning horribly. 

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