i was wondering what could be wrong with my car..at idle it reads 14.4 volts but when it's under load( accelarating) it stays 14.4 and drops to 12.8/or 12.9 consistant. what could be the problem is it the battery, or the alternator? btw my car is 01 with 90k's on it.

thanks

 

With no accessories on, your charging system should produce 15.1 volts or higher at 2000 RPM. At higher RPMs, make sure you have all accessories off when you measure the voltage.

If you're getting less than 13 volts with all of your accessories turned off (including defroster and A/C), you may have a bad regulator, a bad ground, or a heavy current drain somewhere in your car. The regulator is an integral part of your alternator, so your best bet is to clean off your ground connections and troubleshoot for possible current drains.

This problem isn't a bad battery, although this doesn't mean that your battery is good. If you don't have problems starting your car, it should be fine. If it cranks slowly, I suggest you start by cleaning off your battery terminals. Make sure you have the radio code handy before disconnecting your battery cables.

 

Keep in mind that the ECU controls the alternator and turns it off from time to time. Honda's have done this for years. On my other honda's I simply clip the control wire from the ECU and then the alternator acts like a normal one and it stays at 14.5 all the time.

It doesn't overcharge or anything.

It's pin 2 on the 4 wire connector at the alternator or the wht/grn wire from ECU connector C (pin 2 at the ECU too). It's purely a fuel economy thing that's only used in the US and Canada.

The reason I clip the wire is, I don't want the injectors, fuel pump or ignition to see voltage that swings 2 volts depending on the whim of the ECU.

 

Mine has always read no higher than 14.1V, with a low of 13.8V. This has been the case over the last nearly 6 years, original battery, old battery, new battery.

 

If you're diving down the road with the head lights on and the fan blowing, and it's 14.X volts then there's nothing wrong with the alternator. If you're accelerating, it drops to 12.5 and then goes back to 14.X when you're cruising down the road, again there's nothing wrong with the alternator.

If you really want to trouble-shoot this, hook up to that line I mentioned with a meter and see what it's doing while you're driving around. I'll bet the ECU cuts the alternator when you accelerate. Alternately, you can get the thing load tested.

If the battery's 4-5 years old. It's due for a replacement and might explain why you see this much voltage swing.

13.8 - 14.1's lowish in my mind XViper. You have a constant voltage monitor or just metering it from time to time?

 

Ok, viper you had be doubting myself so, I instrumented up the '2k (Fluke meter on the lighter plug) and drove around.

2002 '2k with 4 year old battery.

Driving down the road with the AC, head lights, high beams AC and defroster running, I was getting
14.01 volts.

Driving down the road with all of that off,
14.25 volts.

At that point, I figured I was wrong. But, I pulled into my driveway and noticed the blower was still kind of high. Turned the blower off.
12.69 volts.

Driving down the driveway (about 1/8th mile) with no load on the electrical system other than running the car.

Voltage bounced from, 12.69 to 14.25.

So, my symptoms seem to mirror the original posters. With no load on the electrical system, the ECU turns the alternator on an off.

 

I have a Passport radar detector that has a voltage sensor. It's shows voltage all the time unless it picks up a signal. I confirm the voltage it sees with a voltmeter, so I know it's good. It has been this way since year one, through all phases of batteries and through the heat of summer and extreme cold of winter. The car has never failed me in this regard (or any other for that matter).

 

first thing ill try to change it by replacing my 4 year battery..if this fails..ill check my alternator for a load test

 

B, It's not conclusive that anything's wrong.

Do this test. drive around with the fan running at about 1/2 speed or the headlights on and see what the voltage does. If it's like my '2k, the fan running will draw enough current that the ECU keeps the alternator running at 14+ volts.

The '2k like other honda's has an Electric Load Detector (ELD) this tells the ECU how much currrent the car's using. The ELD seems to be how the ECU determines when to turn the Alternator on and off so, having a 1/2 decent load should keep the alternator on.

 

15.1V i have never seen mine go over 14.4V...