Hey All

A couple years ago, I installed a subwoofer and amp into my 2015 Honda Fit LX. This system was hooked up directly to the car battery with no supporting batteries for the audio and no alternator upgrade. Shortly thereafter, all my warning lights came on including check charge system. Given that nothing seemed wrong, I have driven it like this for two years with no problems. Now I want to sell the car and am already a ton of money into trying to diagnose this and really really want to move on with my life. Oh and by the way, the stereo system has been removed and car is back to stock.

I have replaced the belt and the alternator. The alternator replacement turned all lights off for over a week and I thought that was the solution until they all just came back on today. I am wondering if it is because the alternator is not an OEM part or is the problem something else completely because like i said nothing is wrong with the car it drives fine and tests fine for voltages.

can someone please enlighten me with what is going on

 

Welcome. Regarding warning lights, it is imperative to pull the OBDII codes if you want your problem solved. Otherwise you are literally flying blind.

The working assumption is the aftermarket install damaged the electronics in some way. Maybe a burnt relay or fuse, or damage to the wiring harness itself.

Wiring harness diagnostics aren't cheap, and replacing a wiring harness isn't cheap either. Hope that's not your problem.

 

Honda does have a charging system monitor on the system similar to the system BMW has had for years. Excessive drain or difference between each cold/hot starts might be at play. As the previous poster mentioned - get the OBD ][ codes - the Honda BMS will throw codes.

How it works:
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How the battery sensor works: it measures the current to and from the battery. It may also monitor the voltage, state of charge and state of health of the battery (aging). In some cars, it even measures the temperature of the battery.

The vehicle computer (BCM or PCM) uses these inputs to precisely adjust the charging system voltage, idle speed and other parameters for better fuel efficiency and longer battery life. This system is called Power or Battery Management System or BMS. If the system detects that the battery is getting weak, it may turn off some electrical accessories (load shedding), such as the navigation, heated steering, heated seats, etc., to save the battery power. In this case, the computer will display a warning message on the instrument panel.

 

and the attachment for educational purposes

 

Check for recalls on your VIN # at recalls.gov website. Some Honda's were recalled for Battery Management System on Accords but I see other models may have been included. Road salt was the issue on that design.:
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July 13, 2017 — TORRANCE, Calif.

• Approximately 1.15 million Accord vehicles affected in the United States
• 12-volt battery sensors will ultimately be replaced, free of charge
• Four engine compartment fires have been reported in the U.S. with no reports of injuries

Honda will voluntarily recall approximately 1.15 million Accord vehicles from the 2013-2016 model-years in the United States to replace the 12-volt battery sensor, free of charge. Honda has received four reports of engine compartment fires in the United States related to this issue, all within the “salt belt” area. There have been no reported injuries related to these incidents.

The 12-volt battery sensor is located on the negative battery cable within the engine compartment, monitoring the battery’s state of charge in order to alert the driver to problems with the battery or the charging system. The battery sensors installed in affected vehicles may not be sufficiently sealed against moisture intrusion. Over time, moisture intrusion may bring road salt or other electrically conductive substances inside the battery sensor, leading to corrosion and eventual electrical shorting of the sensor. A shorted sensor can heat up through electrical resistance, potentially resulting in smoke coming from under the hood or, in the worst case, a fire.

Honda will notify registered owners of all affected vehicles by mail beginning in late-July 2017, with instructions to take their vehicles to a Honda automobile dealer. The dealer will check the vehicle for a Diagnostic Troubleshooting Code (DTC) related to the sensor, test the battery sensor and, if it is not functioning properly, replace the sensor with a countermeasure part (final repair). Due to the large number of parts required to conduct the recall, if a vehicle has a battery sensor in good condition, the dealer will apply a temporary repair – application of an adhesive to the battery sensor case to prevent moisture intrusion. When countermeasure parts inventory becomes sufficient, all owners of vehicles that have not yet received the final repair will receive a second mailed notification advising them to take their vehicles to a Honda automobile dealer for the final repair.

Honda is announcing this recall to encourage owners of affected vehicles to take them to an authorized dealer as soon as they receive mailed notification from Honda. Owners of 2013-2016 Accords can also determine if their vehicles will require repair by visiting www.recalls.honda.com or by calling (888) 234-2138.

 

What are the 3 other lights?

Did you test the charging system before replacing the alternator to see if it was actually faulty?

I'm asking these things because multiple warning lights at once on a 2015 Fit is often faulty fuel injectors. I realize that is not related at all to a charging system fault, but Honda likes to throw all the lights on even for unrelated problems.