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Alternator question - I think I need a new one

30K views 14 replies 7 participants last post by  Walkers 
#1 ·
So I think I need a new alt. had the battery replaced last week since it was dead and today on the way home from work I noticed the volt gauge go to almost the 3/4 mark which would be about 16 volts. I assume it's the alt overcharging. We tested the charging system after installing the new battery and everything came back ok.

I was looking at them online and noticed some say with Delco alternator and some say with Bosch alternator. Does that mean it is basically either an AC Delco or Bosch alt with a different manufactures casing? Any one to stay away from? Will prob replace this weekend with from AAP, etc.

My second question is can I replace my 145 amp with the 160 amp? All the 145's are remans and the 160's are new and I'd rather put on a new as as opposed to a reman unit.
 
#2 ·
Hi,

I would go with the 160amp vs the 145amp. New vs. old. Depending on how much power you draw from your current electrical system, it will help. Extra power items are, Amps, High output fog lamps, cell phones, any electrical device plugged into your cig lighter, etc...

I placed a 250amp in my truck from here: DB Electric

I have not had a problem with the electrical system in 2 years.

Take care, :)
 
#4 ·
Well it looks like my alt is bad. Here are two pictures of the gauge today. Both were taken at idle but it did the same thing while driving. It wouldn't fluctuate quickly but at random. I would look down and its dead on 14 then look down about 5 minutes later and its a good bit below 14.. I tested it with a volt meter I have at the house and the highest number I got was about 15.1 and the lowest was about 12.4 (this was at idle). Then went to Advance and had them test it. The voltage was only running high when we tested it at about 15.1 (same as I got) but it never dropped below 14 at Advance (it did it again on the way home though).

I'm thinking it's the voltage regulator in the alt but I'll replace the whole thing. The good thing is that I won't be driving my truck for 2 weeks starting tomorrow so I can replace it when I get back since the part won't be here before we leave. I'll just pick up a new AC Delco from Rockauto for $157 vs. AAP (ToughOne) for a remaned for almost $190.

I did notice that my truck has the DR44 alt (KG3 RPO) on it now but the 145 amp on Rockauto and AC Delco's part site has the DR44 as the 160 and DR37 as the 145. Mine is stamped with 145 A. Did they change the casings at some point or does that even matter?
 

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#6 ·
wildchevy said:
Your truck probably has a PCM controlled alternator, it common they will run the voltage at 12.5 for periods of time, helps fuel mileage and is normal.
Agree. Do nothing but monitor the situation. The voltmeter in my 2012 does exactly the same thing. Not sure it's for economy....probably has more to do with battery conditioning than anything else.
 
#9 ·
Yep, it might go a hair above 14 but never to almost the 1/4 mark or to the 3/4 mark. My dad's GMT-900 Avalanche doesn't do this either. I can understand that the alt and PCM would adjust voltage to the truck but not all the way down to 12.5 volts or up almost to 16.
 
#11 ·
From the manual,

The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 5 volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.

Battery Sulfation Mode

The BCM will enter this mode when the interpreted generator output voltage is less than 13.2 volts for 45 minutes. When this condition exists the BCM will enter Charge Mode for 2-3 minutes. The BCM will then determine which mode to enter depending on voltage requirements.

Charge Mode

The BCM will enter Charge Mode when ever one of the following conditions are met.

•The wipers are ON for more than 3 seconds.
•The GMLAN Climate Control Voltage Boost Mode Request is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.
•The estimated battery temperature is less than 0°C (32°F).
•Battery state of charge is less than 80 percent.
•Vehicle speed is greater than 145 km/h (90 mph)
•Current sensor fault exists
•System voltage was determined to be below 12.56 volts
•Tow/Haul mode is enabled
When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9-15.5 volts, depending on the battery state of charge and estimated battery temperature.

Fuel Economy Mode

The BCM will enter Fuel Economy Mode when the ambient air temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 amps and greater than −8 amps, and the battery state of charge (SOC) is greater than or equal to 80 percent. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5-13.1 volts. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.

Headlamp Mode

The BCM will enter Headlamp Mode when the headlamps are ON. Voltage will be regulated between 13.9-14.5 volts

Start Up Mode

When the engine is started the BCM sets a targeted generator output voltage of 14.3 volts for 30 seconds.

Voltage Reduction Mode

The BCM will enter Voltage Reduction Mode when the calculated battery temperature is above 0°C (32°F). The calculated battery current is less than 1 amp and greater than −7 amps, and the generator field duty cycle is less than 99 percent. Its targeted generator output voltage is 13 volts. The BCM will exit this mode once the criteria are met for Charge Mode.
 
#13 ·
etcthorne said:
wildchevy said:
Your truck probably has a PCM controlled alternator, it common they will run the voltage at 12.5 for periods of time, helps fuel mileage and is normal.
Agree. Do nothing but monitor the situation. The voltmeter in my 2012 does exactly the same thing. Not sure it's for economy....probably has more to do with battery conditioning than anything else.
i'm reviving an old thread - dont get angry, it means i used the search function.

For about 4 days now i've had an intermittent P-0621 code with Battery light and "service battery charging system" alert on the DIC. The alternator tested good (with the DIC alert and light off - code not active) at both advance auto and autozone. thinking this meant it was the PCM i took it to the dealer (PCM still under warranty)...the dealership came back and said it was the alternator despite the 2 good tests. Dealership reported it getting down to 11.4v while idling and their tests reflected 587 cca on a 45 day old 730cca battery.

would you still recommend just monitoring or should I replace it?

If i have to replace it, im considering putting the 160amp in instead ($20 extra for new vs reman is cheap insurance and gives some flexibility for future).

thanks in advance.
 
#14 ·
our Trucks have a Governed charging system, which means the PCM is controlling amperage and draw on volts, it takes what it needs when it needs it. This is to help save on wear and tear on the entire charging system throughout, and also as they state to help with MPG's, so to see your volt gauge fluctuate from12-16 volts is NORMAL.
now you can help the system from dimming/flickering lights by adding/upgrading your ground wires, your battery alt feed wire, and chassis grounds. also make sure your battery is a top knotch not just some cheap knock off because, remember you get what you pay for. you can also upgrade your alternator to a higher amperage because the PCM will only take what it needs. Google your questions because a lot of people have figured out different ways to help this annoying issue, just do your homework and be safe kids!
 
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