My 2004 has been doing some strange stuff lately, and I'm trying to track down the issues.

One thing that keeps popping up in the back of my mind, is how hot (voltage-wise) the car keeps running.
The battery checks out good, it is a newer battery, and the connections to it are tight and clean.
But, when running at highway speeds, the car has been running at about 15 volts, sometimes climbing to 15.1 or 15.2V.
If I put a huge load on the system, it might drop down to the high 14s. Backing up at night really tags the system, since I have extra backup lights, plus brake lights, plus foglights, plus everything else, and I've seen it drop to mid 13s at the extreme ends.

Now, these readings are from the DIC, but all have been verified with a DVOM.

The positive cable on the alternator is in good shape, no damage or corrosion.
I see some corrosion on the ground cable running from the engine block to the passenger side fender. I've cleaned that, no change, but the gunk keeps coming back. The connections on that cable are clean, and tight as well.

I know the voltage regulation is done by the PCM, so I doubt taking the alternator to be tested will show any issues. It is plenty capable of the amperage loads.

Where else should I look? What else can I test to try and get this crazy voltage under control? Its killing lights, my dash lights, headlights, and other electrical loads. It just took out a year old HIR bulb, my radio lights are all out, and I'm loosing the bulbs in my steering wheel controls that are less than 2 year old, new from the dealer parts. Both my seat heaters are shot, and now I think the ignition module is starting to have issues.

Ive mostly just been watching the DIC for information, but it seems to be reading accurate. Every time I've checked it against a known good DVOM, it has been spot on.

if your car is the type that is regulated by the computer, you need to find where the it gets its reading from, because if thats corroded and showing low voltage it will crank up the actual voltage to compensate


edit found diagram if you dont have one.

Thanks Justin.
Ok, I do have the FSM here, reading through it. It does appear that this alternator has an internal voltage regulator, and its not just the PCM controlling the whole show.

The PCM has never thrown a code for this, and its never exceeded limits that cause a DTC to set. (Which are pretty high, IMO.. 16+V? Ouch!)
So it sees 15.0, 15.1 as being within "normal" range, so the PCM never does anything to correct it. But I don't think it has any sort of monitoring for just how long that 15v is going to the system (which is all the time, pretty much.)

Despite attempts to clean the contacts, wires, and make sure the grounds are good, and the battery is ok, it seems like the generator is running off on its own, and the internal voltage regulator isn't working right. It seems to try and keep the system stable at 15.0V, rather than a more reasonable number. And its always run hot, ever since I got the car. I just figured this was normal, but I think its causing long term problems with things running at that kind of voltage for extended periods of time. (Like lights burning out quickly, heating elements going bad, etc).

The only thing I can actually see being a possible problem is the main ground cable keeps corroding. Maybe I can start by replacing that, and see if it helps.

If I were to take the alternator out, and have advance auto test it, can they tell if the internal voltage regulator works or not? Or is it a simple works/not works type of test? Anyone know? If I can have them test the internal voltage regulator outside of the car, and isolate the alternator from any other problems, maybe its gone bad. But the PCM doesn't see it as a problem, since its still an "acceptable" voltage.


But honestly, I've read in several places where these cars tend to run hot (on the voltage side). Is running 15V constantly, considered "normal" or is that on the extreme end of things? I just want to be sure I'm replacing something that is a real problem.

And the only place I see a battery + output, is directly to the RIM. The PCM has generator on and off signals, but they are output around 5V just to turn it on and off. I think the only reason the RIM has any type of voltage sense circuit is for load shed if the system can't keep up with demand. But, since 15V is within "normal" spec, it doesn't have a problem.
I don't see where the PCM actually controls the output voltage of the alternator at all, other than to turn it on and off.
Since its been a constant problem, exactly like this for over 2 years now, I'm beginning to think more now that its the alternator. If there were a wiring problem, or it just started, or was an intermittent problem, then maybe a connection, or a wire might be the problem. But its always been like this. I'm just starting to get a bit peeved at it, because I'm seeing the lit steering wheel controls, and other interior bulbs I've replaced, go bad after being in there less than a couple years. Not to mention it killed my year old HIR hi beams. Stuff like that shouldn't be happening.

was reading and found this, so as long as the voltage is just an on or off 5v the voltage is regulated internally. if the turn on is pwm the ecm is controlling it

"The engine control module (ECM) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The ECM uses the PWM signal input to determine the generator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads.

The ECM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the ECM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5 percent and 100 percent. The ECM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the ECM detects an out of range PWM signal, DTC P0622 will set. When the DTC sets, the ECM will send a class 2 serial data message to the instrument panel cluster (IPC) to illuminate the charge indicator."

In the FSM:

"When the engine is running, the generator turn on signal is sent to the generator from the PCM, turning on the regulator. The generators voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator field terminal is connected internally to the voltage regulator and externally to the PCM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the PCM that a problem exists. The PCM monitors the generator field duty cycle signal circuit.

It sounds like the PCM isn't really involved that much in the process? Sounds like all the voltage regulation is done in the alternator, and the PCM only gets involved when things really get out of hand and the alternator can't keep up with demand. At least, thats what I read into this.

I mean, if the alternator was cheap, I would just replace it and see if the problem is solved. But at the prices I'm seeing delco-remy ones go for, even reman ones, ($200+shipping+core up to nearly $300) this isn't something I can just throw in there just in case it solves the problem.
I'm already looking at $400 to replace the fuel lines this week, another ?$ to replace my HIR hi beams.... ugh. I can't afford a $300 "guess" at a fix.

maybe one one of the parts stores would let you try it and bring it back

What alternator do you have?
I may be able to find a rebuild kit for you, and a video on how to do it, I was able to find a repair kit for my DELCO CS144 EARLY SERIES for 41.00 on ebay.


Do you know if your alternator is 105A, or 140A?
If it is the GM AD230 or AD244 you can get the voltage regulator for about 40.00, it should not be hard to replace, if it is the alternator the voltage regulator would be what I'd think would be the problem.

http://store.alternatorparts.com/regulator-11.aspx



Exploded diagrams of both, since it is probably one or the other.]

http://www.alternatorparts.com/xad230.htm

http://www.alternatorparts.com/xad244.htm

rock auto lists it as a ad230 105a

I don't think that you have a problem. What voltage would make you happy? My car runs at about 14.6v. I don't think that .5 volts will make a big difference on the life of your bulbs. You can dim your dash lights. I am sure that your ICM isn't affected by 15 volts. The seat heaters burn out anyway. You could install some series resistors in your headlight wiring if you want them to not be so bright and last slightly longer. If the voltage was 17 or 18 volts then I would be concerned.