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pcm control causing my voltage problems?


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I have a 2009 chevy Silverado and just added a 250 amp alt. All big 3 done with true 0 gauge wire. Have added 1 extra optima yellow top that matches my existing starting battery. My voltage starts out great at around 14.9 to low 15's then after driving it will dropp to low 13's. I've allready posted about thinking my alt was the problem. I do have a soundqubed 3500.1 and an xtant 3300c. I am wondering if this module is possibly the cause of my voltage issues. Cause when I first start my truck and its in charge mode it has no problem keeping up but once it cuts back on the voltage it doesn't seem to be able to catch back up. I do plan on adding better batterys but I'm tight on cash and having to rebuild my system after some a-hole broke into my truck and stole everything I had. And of course I had never thought to get an extra writer on my insurance so I lost it all. But any help on how to bypass this module if that's the problem would be appreciated. And my truck does have only two wires going into the alt other than the main power out.

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Just takethe bulb out our paint over the battery light if you by pass the pcm. Most ALTs only charge in the mid to high 13s hot. specially if there is no demand

t1500bdcp

2 t2d4 15"

1 t600.4

1 t400.2

1 set p1 tweets

singer alt, tons of wiring, smd vm-1, 80prs, back seat delete, still in the works, aiming for a 145-147 with the ability to play 25hz up to 50hz.

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Thanks. I think I'm going to get the bracket kit to add a second alt that way I can use one just for my system and bypass all the factory equipment and run it straight to my batt bank for my stereo and keep the other alt hooked up factory . I plan on getting another soundqubed 3500.1 so ill need the extra amps.

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With that unpluged will it keep voltage up? I have played around with accessories in my truck like fan /ac and have noticed that with them on it seems to keep voltage reading higher than when I turn them off. Ill try unplugging that sensor. Thanks

If you unplug it the PCM will go into a default charge of about low to mid 13's

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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.

@Mechman is alot more knowledgeable than me but it has worked for me in my cobalt and silverado. With the sensor unplugged i was told it'd operate just as a regular alternator.

Helix P SIX DSP

Audiofrog GS10/GS60

Hertz HSV165XL (Rear Fill)

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if you still have the stock alt you can get a bracket for dual alt like you said and put the stock alt back on in the stock location and the ho alt on the bracket with an external regulator.

t1500bdcp

2 t2d4 15"

1 t600.4

1 t400.2

1 set p1 tweets

singer alt, tons of wiring, smd vm-1, 80prs, back seat delete, still in the works, aiming for a 145-147 with the ability to play 25hz up to 50hz.

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Share on other sites

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