Need help with "Service Vehicle Charging System"

[dkad260]

While driving tonight I had this message, voltmeter on dash went down to halfway between 9 and 14.

I pulled over and restarted and no change so I drove 5 miles home. While driving home the volts went back to a little over 14 but the service charging system message still persists.

I checked the alternator output and I now have 14.8 V so that seems high.

I measured the battery POS terminal while running and it also has 14.8 V so I assume the 175 A fuse is good.

Does this sound like the regulator is going out?

I had to edit this because I couldn't call the big fuse by it's name? It won't let me type "maxifuse"

 

[dkad260]

Update....replaced alternator.....all is good.

 

[Joseph Garcia]

Thank you for posting the solution to your issue. Our collective knowledge base has been increased.

 

[dkad260]

What made me seek advice, was the volts seemed to return to normal, the big fuse was good, the alternator was charging, but I still had the DIC message about the charging system. Replacing the alternator on a whim is $$$ but it was the OE unit so was peace of mind at the least.

 

[MWD_CTSV]

The DIC is from the ECM which compares the input control to the expected output. The ECM is limited to knowing the duty cycle control which it is sending to the alternator and the actual voltage at the ECM. So a fault anywhere in that path between could trigger the DIC message.

For the DR44G series alternator, I would say based on the rebuilder parts availability, it is mainly just the 'wear' items, the regulator, brushes, and shaft bearings that go bad, so overall the alternator is very reliable. If the brushes are worn out, I would expect low voltage or not enough output. If the regulator fails, it could be all over the place including low voltage, varying voltage, or full voltage (15V), but the ECM would most likely warn you via the DIC that something is wrong.

If the rectifier fails, the voltage could be low at idle (especially under load with fans and lights) and/or a DIC message about the charging system, but the voltage would likely improve at say 2000 rpm, but still be low.

A rebuild kit with bearings, regulator and brushes is $40. The regulator and brushes are just boltons, so an easy fix, especially a low cost one if the bearings spin freely. Adding the rectifier is another $40, and it has to be soldered on, which is not as easy, so at that point it is probably better to pay for the new GM alternator at ~$250.