davidyeh27

Hi--
I have a 2015 RDX, purchased in Fall 2014. Woke up to a non-starting car, got it jumped and took it to a shop to get the battery changed. After changing, it started up fine, but the shop guy commented that that was something odd about the voltage readings. With engine running at idle, his meter read about 12.3 volts, which he says was abnormal, it should be in the 13.5-14 range (and I confirmed this with other articles that I found on the web). However, when he flipped the headlights on, it went up to 14.3. He thought it was strange that there was such variance, and suggested I have it inspected to make sure there was not an alternator problem that would prevent it from being properly charged at all times. However, when I went to another mechanic, he noted that this particular model (as well as other Acuras, Hondas, and Toyotas, but not necessarily other makes) have a battery sensor that is different from a conventional battery/alternator setup, which regulates when the battery is charged, so that it is not necessarily charging all the time; if the battery is full and not stressed, it might not be charging and read 12 volts even with engine running, but when the headlights are flipped it responds to the demand and the voltage goes up.

Anyone knowledgable enough about this to comment if this is accurate, and I have nothing to worry about? I found references to this battery sensor part at places that sell replacements, but none that describe its function in detail. Thanks.

dave08902

DESCRIPTION > CHARGING SYSTEM DESCRIPTION - OVERVIEW (2013-17)

The alternator outputs the power corresponding to the electrical power consumption, varies to multi stage and acquires the reduction of the fuel consumption by proper output control.The battery sensor attached on the battery negative terminal measures the current value, voltage value, battery temperature, and internal resistance changes to the signal and sends to the PCM. The PCM calculates the proper AC output based on the received data and sends commission data of the proper generating to the alternator for the required generating.

Output Voltage (PCM can choose a value between 12.5 and 14.5 volts in 1/10th volt steps.)

• Depending on the vehicle condition, the variable control is not activated.

When the alternator is faulty the following DTC is memorized.Refer to the troubleshooting.

• P1549: Charging System High Voltage
• P0562: Charging System Low Voltage
• P16BB: Alternator B Terminal Circuit Low Voltage
• P065A: ACG No Charging Malfunction
• P16E4: ACG High-temperature
• P16E2: PGM-FI-ACG LIN Communication Error

davidyeh27

Thanks! This sounds like what the mechanic was describing, that the battery sensor allows for variable alternator output.

dave08902

You're welcome,
Happy to help. At least you responded, most people here don't answer back or respond to their posts they started.


The alternator also has a decoupling pulley. All this is improve gas mileage.

Tech

Honda has had a Dual Mode Charging System since the early 90s. See attached file at the bottom of this post.

I believe my 2013 VW Jetta had a similar type of charging system as well since I saw voltages all over the scale. And on my other car, I have seen voltages (it has a digital voltmeter) of 14.8V and as much as 15.0V at ambient temperatures of 3C to 6C. I am not used to seeing such high voltages for what I think is a flooded lead acid battery (it does not appear to be an AGM).

Note the negative terminal on your Acura battery and you should find one of these instead of a simple clamp.



My other car has one of these attached to the negative terminal. You can see sensor wires connected to the top left of the battery clamp. At a minimum, it might be a temperature sensor which is needed for proper battery end voltage charging.