Hey guys, I believe I have stumbled across the ECU bypass for the alternator charging system by accident.

I have a voltmeter hooked up to my cigarette lighter port, and noticed it would shift from 12v to 14v sporadically. After hours of research, I found there's a smart system that cuts the alternator on and off when demands are high or low to extend the life of the alternator. For many of us running an aftermarket audio system, we're struggling with the undersized alternator output and can't afford for the charging system to decide "low demand" and drop our alternator output randomly.

On your factory battery negative post, there is a small black battery sensor with a 3 wire connector. If you disconnect this and start the car, you will get an error code "Check Charge System"..... BUT you will be at a constant 14+ Volts! You can also pull the fuse for your battery sensor but it will also cut your DRL (daytime running lights) in the Gen. 3. It is either fuse #15 or #17, both 7.5 amp fuses.

I have been running my Fit this way for 6+ weeks with no issues yet. I purchased a shunt and an ammeter to read my amperage draw on my charging system with the battery sensor connected vs. disconnected. I'll post results when I set everything up.

I will also be upgrading my alternator to a 280 amp output in the upcoming weeks. I'll post a new thread once it's complete hoping the ECU bypass allows me to pull more than 100 amps LOL.

 

I am just speaking from experience and what has worked for me.

 

Thanks for the information.
You are correct the Honda system looks at the battery voltage and the current draw on the system all the time. When battery voltage is high enough and demands are low the computer turns off the alternator to allow it to free wheel and help save on gas. I installed a voltmeter on my 2015 Fit and watched this in operation. The first time it happened I thought alternator went bad. It went from 14.2 volts down to 12.7 volts which was battery voltage without alternator working. I ran for 20 miles while the battery voltage went down to 12.4 volts before the charger came back on. cruising down the road with charged battery and low load will turn off alternator ouput. If I want to turn alternator back on just turn up radio , turn on lights, or AC compressor to draw more from battery and the ECU will turn it back on and voltage will bt 14.0 volts charging. If the ECU does not have information from sensor it will put charger message on screen and run alternator constantly to keep battery charged.
Did you remove the black sensor from the car or just unplug connector?

Looking forward to your charging information charts.

James

 

I just disconnected it. In the process of running it on a switch so I can turn it on and off whenever I like. There’s just a 3 wire connector you have to unplug and I just leave it resting on the battery with the terminals taped up.

 

I thought about the switch idea also. That way you can flip switch like you want and then crank up. That might be a way to make sure the battery is fully charged in the winter which will help on cold starts. With the battery fully charged it might let let Fit sit longer between starts without battery being dead.

Keep up the good work


James

 

Thanks man. Don’t have that issue here, South Florida is not forgiving haha. I’ll post up some more stuff soon!

 

do a serch for " honda eld" in google or a civic forum... there are diagrams to build a switch with a relay. on my 2019 sport, i get 14.4 v when i have lights on, or fan switch is at 3 or 4 these are the pnly way i can get 14.4 volts, sometimes its a 14.4 with out but most of the time im at 12.3v if my lights are off or fan switch is at 1 or 2. its common on most hondas from 1995 and up