I'm wondering what would cause this code to come up. Ever since the weather became cooler my car has been spiking in voltage. I'm not sure if the 2 are related or just coincidental timing. For the most part though my car stays around the 14.3v but the last few days its been jumping around from 15.5-18.5v. What could be causing these problems?

The battery is brand new, I purchased it over a month ago. The alternator was tested and I was told is functioning properly (twice). I've checked all the wiring to the battery, alternator, and starter. I made sure connections were secure and clean. What else could be causing this?

To me it sounds like the voltage regulator in the alternator but unfortunately for me unless the alternator finally craps out, I can't get it fixed under warranty. I don't really wanna buy a new alternator when this could be repaired for free but if it continues will the high voltage start burning out my electronics? What else could be causing this?

Go figure that twice now its been putting out high voltage for a couple days in a row so figuring the problem will stick around for a third, when I go somewhere to have it tested, it works fine. Anyways, are there tests I can do that will definitively tell me its the voltage regulator? Otherwise I'm open to testing other stuff to solve this problem before I put it in storage.

Thanks guys.

 

I don’t know what you warranty situation is but you can't leave it like that, it may damage your electronics as you thought.

Is only the alternator under warrantee. If they did the work, I would pay for the regulator and see if I could get them to go real easy on the labor rate.

After my car sits it initial charging voltage is close or at 15 volts. After a while it finds its way down to about 14.3 or so. But it never gets back to 15 at any time after that.

My only other suggestion is connect a DVM to some 12 volt point in the car and just leave the meter on when you driving so you can compare the voltage. You might have a measurement problem with the car and a independent meter will give you the truth and correlate the results. If the DVM goes up with you dash indication, then it's the alternator probably.

That error code 51 indicates the PCM thinks the voltage has hit 17.1 volts. You should get a MIL light and it will start shutting down transmission functions.

 

What Pcolt said.

 

You need to check voltage at both the battery and at the alternator. Use a DVM to check output. If the alternator is putting out too high a voltage, then you should be able to get it replaced under the warranty.

Chances are it's the regulator and that is an internal part so it's covered under the warranty for the alternator.

Too high of a voltage will kill or really harm the electronics.

 

I finally caught the problem with a meter hooked up, I do read high volts at both the battery and the alternator.

I did notice that when the voltage shoots up the car sputters like it wants to shut it down. I'm taking it off the road till I get it figured out. I may take the alternator off and have it tested one last time, if they say its fine then I'll buy a rebuild kit and change the regulator myself.

Is there a chance I could have a short somewhere in my system and its causing the alternator to allow more voltage? Or does this just sound like the typical regulator dying?

Thanks for the responses though, its nice to have help verifying problems before throwing money at it.

 

The only thing I can think of the cause the voltage to spike around is the battery. It happened to me, voltmeter was all over the place but was not the vette. It was a bad battery and happened just that fast while I was on the road. Pulled into a sears parking lot (was real close & no other options) and bought a battery. It was a bit of a guess at the time but I guessed right and had I think just a pair of pliers with me. Here in the Florida heat batteries don’t last too long reliably, 2-3 years then you're on borrowed time.

But you said it's a new battery and I guess in your situation installing a new regulator might be a good choice.

 

A short or high load can cause a voltage surge, but only momentarily.
Here's what happens:

The short or high load pulls the voltage down.
The voltage regulator compensates by increasing the field coil current.
The voltage comes back up.
The short or high load goes away.
For the short time (.01-.10 seconds) that it take the field coil current
to collapse, the voltage goes up because there's high current in the
field coil, and low load.

Starting the car is a high load. This happens somewhat everytime you
start the car. It's bad for bulb life to start your car with the lights on.


Chuck

 

Change in the weather goofs my batterys all the time. Some how it either causes bit of corrosion between the cable & the battery terminals, or makes the corrosion thats already been in there, react to the temperature change and act like variable resistor. It drives the regulator nuts! Voltage too high;voltage too low.. I cleaned my battery cables and usually the problem goes away. Other times the weathers temperature change is all thats needed to set the death toll for the battery. New battery and no more problem. Look for the simple stuff first.

 

Your alternator is dying.

 

Replace the alternator--none of the modules,electronics,bulbs etc will stand for that kind of voltage spike for long !! If you can't get the alternator warrantied, DON'T drive it as it is or you'll end up spending a lot more then the cost of a second alternator JMO