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.
How much of that testing can be done with a scan tool, with both bidirectional control & pid data?
Albin, these are the pids I look at when I'm dealing with a Honda. Using the scan tool I can see current at the battery indicating whether it's charging, discharging, or neutral and I can see total amp draw through the ELD pid. Turning on the headlights will produce charging voltage if the alternator is good. I've had two within the past couple months sent by AAA for charging problems. The
Most vehicles have a desired and actual voltage pid. These two pids are very helpful when testing for a charging problem.
I agree actual and desired charge volts are golden pids. I also appreciate the systems such as the Ford products that report commanded and actual regulator control.
Like I've said A LOT of times, if you just wait long enough, everything seems to come back. Honda did something VERY similar years ago and techs kept mis-diagnosing it as a bad charging system, They called it a "HF" series of Honda, that meet High Fuel Economy because at idle and low RPM it didn't charge or charged very low. Even way back then, I kept saying "You have to know your OPPONENT"
Appreciate the information,although it is not new at all with Honda. Honda has been using the ELD as the go between for years on their charging systems and they behave in pretty much the same way as described above.
I agree Rudy but it my corner of the world I see these misdiagnosed often. Just trying to pass along some info that might save an incorrect diagnosis. On the eld system though those alternators would show some charging voltage at idle. The eld was used for high electrical load compensation. If I remember correctly. On these newer systems where the sensor is on the negative terminal that
Honda has been using the eld system since the mid 90's. Also, Honda is very good with chraging data PIDS. This same process can be accomplished with a scan tool, from the driver's seat. Nice little article, thanks Bob!
Id like to start by saying thanks for sharing this case study. This one is very interesting to me cause im actually now working on understanding more the charging system operation on these newer Honda.I recently tested the alternator output on a known good 2017 Accord and yes at idle i got 12.5v and with the headlights on it will raise up to 14v but when adding more loads(rear defroster,AC max…