Honda Charging System Testing
2012 Honda Civic Charging System Testing
The alternator control on the 2012 Civic consists of single wire Lin bus controlled alternator, a battery load sensor, the instrument cluster and the PCM.
This system requires a different approach for testing. At an idle with an adequately charged battery and no load the alternator shows no charging voltage increase. This voltage gives the illusion that the alternator is not functioning properly.
A scope of the single control wire for the alternator shows a good control signal.
Then the battery current sensor is scoped for a proper output signal. A good signal is witnessed.
Now the electrical demand is increased by turning on the headlamps. Almost instantly the battery voltage increased to a normal voltage signal.
With the lights still on and a charging voltage correct at the battery the battery current sensor is scoped. It is obvious there is much more activity on the Lin bus indicating a higher electrical demand.
Now to verify the system the Lin bus at the alternator is scoped with the high electrical demand. Again a more active Lin bus signal is observed.
Other mandatory charging system tests should include voltage drop testing the battery cables. The negative should be tested from battery negative to the alternator case. The positive side should be tested from the battery positive to the alternator battery cable connection. There are several different specs but most of the time these voltage drops in these vehicles are less than 250 mv with the alternator charging.
Hopefully this clears up some confusion as to how a newer computer controlled charging system works. It is extremely important to understand how the system works before testing. There have been instances where these alternators have been replaced for no charge output at idle. It is completely normal that there would be no charging output at idle.