2006 Accord EX, V6 3.0, automatic transmission.

For some reason, my car is overcharging. To the point where it burned out both low beam headlights. Using a digital multi-meter, I found the system is charging up to 19+ volts. I pulled the alternator first thing the next day and had it bench tested at an auto parts store. It tested fine. As did the battery. I checked for continuity on the battery ground and alt to battery power lead-both good.

I put everything back together. At idle, no load, just after start up, it registered around 14v. After putting load on it, revving it up, and letting it settle back to idle, it went up to around 15.5v. Took it to auto store and had system tested while running. Just under 14v at idle, under load, or revved up. No issues indicated on tester.

When I got home, I checked it again. Over 19v! Shut off and restart-over 18v. Let it cool down for a few hours, over 17v.

Really not sure what's going on. I suspect the voltage regulator, but not sure since the store indicated everything was good, in and out of the vehicle. Anyone experienced similar and have an idea what I can do next to diagnose the problem? Any help would be appreciated.

 

Not exactly sure on this one but there could be a problem with the ELDU (electrical load detecting unit) which is located in the under hood main fuse panel. The ELDU senses load and cycles the alternator on and off to meet load demands and by doing so when shutting down the alternator increases fuel efficiency over the long run. Older Civics had a problem with them where the car would not charge thus leaving the vehicle stranded, but I have not heard of you particular issue or any issues with the ELDU on your vehicle.

 

The alternator is overcharging if the readings are 17, 18, 19 volts. For the Denso alternator on the 2006 V6, generally readings over 15.1 volts with no load, indicates a problem with the alternator.

 

The ELD unit would not cause the alternator to overcharge. The ELD unit, together with the ECM/PCM can control the alternator's charge mode; however, the alternator's internal voltage regulator suppose to control the alternator's maximum voltage output.

 

I would think intermit overvoltage, voltage regulator. When you replace alternator get a guarantee one . I suspect that when they rebuild these that intermit voltage regulators get overlooked.

 

Thanks for the advice, guys. Tried duplicating the problem today, but no luck. It tested good in all conditions. Right around 14v every time. Hot, cold, load, no load, after and before driving. Not a glitch. Seems to be no discernible pattern. I'll keep trying to pin it down and report back.

 

Check all the little wires to/from the alternator.

Not sure about this, but looking at the parts drawing I don't see a voltage regulator. Redbull, have they moved that function into the PCM? If so, there has to be a signal wire to provide a voltage measurement to the PCM. And there also has to be an excitation circuit that the PCM uses to control the alternator output.

It looks like it's not as simple as the older control wire that just switches the alternator on & off.

 

The voltage regulator is internal to the alternator.

Honda's utilizes a dual mode charging system to increase fuel efficiency and reduce drag on the engine on start-up. The ECM/PCM determines charging based on info. from the ELD. During heavy load, the ECM/PCM can set charging voltage for high output (~14V - 15V). During light load and start-up, the ECM/PCM sets charging voltage for low output (~12 - 13V).

Most previous generation Hondas had alternator/voltage regulators which utilize five terminal wires: Ignition (IG), Control (C), Field Reference (FR), Battery (B), and Lamp (L). The wires between the alternator's voltage regulator and PCM are the C, FR, and L wires. See attached image.

With that said, although the ECM/PCM can control charge modes (high or low output), the alternator's internal regulator should still limit the maximum charging output.

Just for info.: Starting with the 2013 Accord, the wiring circuits changed between the voltage regulator and the PCM. The 2013 Accord alternator/voltage regulator utilizes two terminal wires: Local Interconnect Network (LIN) and Battery (B). The alternator voltage regulator has one wire (a LIN wire) going to the PCM. I posted the 2014 Accord charging system circuit diagram for KHA's info. at post #125 (if you're interested) in his thread:

https://www.hondaaccordforum.com/for...-32726/page13/