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Discussion Starter · #1 ·
I have a small accessory plugged into my OBD port to give me some info on the car. Whenever I start it it's always running at 13.7-14.6 volts. After I while it will always return down to 13.7. However lately I've been noticing it will drop to 12.4-12.6 while the vehicle is still running. Right now I am plugged into a station charging, the car is on to run the AC and it's sitting at 12.2 volts, which is the first time I've seen it this low while the car is on. I've taken it to 3 mechanics now that swear everything is fine with the car. Is this normal operation for the Volt?
 

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2011 Premium, Nav (added back-up camera! :)
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everything other than the 12.2V seems familiar to me in my 2011 Volt. 14.5 or more on start up, then it settles out to about 12.6v. If you have the headlights on it will run at 13.5 or so. 12.2 seems a little low...
 

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Is the voltage reading via OBD-II or off the battery? If it isn't directly from the battery, you have no idea what is actually going on there... The voltage reading at the OBD-II connector (or ECU or whatever) isn't necessarily battery voltage. It would make sense also that the Volt doesn't always charge the battery, just holds it at a float voltage for much of the time the vehicle is operating...

Also note that battery charging voltage is temperature dependent, so maybe you are in the middle of a heat wave?

-Charlie
 

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Discussion Starter · #4 ·
Holding it at 12.6 would make sense. I just don't know a lot about cars and I've always heard cars run 13.6-14.6 when on. I guess I figured the OBD was wired straight to the battery, but you could be right. But yes it also has been 80-100 the past week or so.
 

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2012 Std w Nav
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The AC compressor runs off the HV system, but the pumps and blowers are low voltage. I don't know offhand how far down they might draw the voltage from the APM.
 

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2011 Highlander Hybrid, 2017 Volt Premier
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That's strange... According to the Gen.2 service manual, in case of lower than 12.56 V your car should enter Normal mode and charge the battery (outlined RED). The charging system is a little bit complicated:
Charging System Operation

The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
  • Battery Sulfation Mode
  • Normal Mode
  • Fuel Economy Mode
  • Headlamp Mode
  • Voltage Reduction Mode
  • Plant Assembly Mode
Battery Sulfation Mode

Battery sulfation mode is used to help maintain the battery life. The charging system will enter a battery sulfation mode which tries to increase the vehicle charging when the charging system voltage is less than 13.2 V for about 30 minutes. Once in this mode, the BCM will set a targeted output voltage between 13.9 - 15.5 V for about 5 minutes. Following this 5 minutes, the BCM will then determine which mode to enter depending on the system voltage requirements.

Normal Mode

The BCM will enter Normal Mode whenever one of the following conditions are met.
  • The wipers are ON for more than 3 seconds.
  • 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).
  • Vehicle Speed is greater than 145 km/h (90 mph)
  • Current Sensor Fault Exists
  • System Voltage was determined to be below 12.56 V
  • 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 V, 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 greater than -8 A but less than 5 A, and the battery state of charge is greater than or equal to 85 percent. Its targeted APM set-point voltage is the open circuit voltage of the battery and can be between 12.6 - 13.2 V. The BCM will exit this mode and enter Normal Mode when any of the conditions described above are present.

Headlamp Mode

The BCM will enter Headlamp Mode whenever the high or low beam headlamps are ON. Voltage will be regulated between 13.9 - 14.5 V.

Voltage Reduction Mode

The BCM will enter Voltage Reduction Mode when the calculated battery temperature is above 0°C (32°F) and the calculated battery current is greater than -7 A but less than 1 A. Its targeted APM set-point voltage is 12.9 - 13.2 V. The BCM will exit this mode once the criteria are met for Normal Mode.

Plant Assembly Mode

The BCM will increase charging voltage for the first 500 miles of operation in an effort to ensure that the 12 V battery is fully charged when the vehicle is delivered to the customer.

On the other hand, it's stated, that:

This vehicle is equipped with a regulated voltage control system. This will cause the voltmeter to fluctuate between 12 - 14 V, as opposed to non-regulated systems which usually maintain a more consistent reading of 14 V. This fluctuation with the regulated voltage control system is normal system operation and NO repairs should be attempted.
 

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Holding it at 12.6 would make sense. I just don't know a lot about cars and I've always heard cars run 13.6-14.6 when on. I guess I figured the OBD was wired straight to the battery, but you could be right. But yes it also has been 80-100 the past week or so.
That 13.6-14.6 is the old standard for flooded lead acid batteries with 'dumb' alternators. Modern (say, last 10 years or so) vehicles and charging systems have a much wider range of 'correct' operation depending on a number of factors (battery type, battery sensors, calculated battery needs, etc.). Even normal ICE cars will the alternator in a lower voltage/float mode sometimes for fuel economy reasons.

-Charlie
 
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