View Full Version : low voltage???
09-14-2012, 06:54 PM
Hi im new here and i have a big question, i have not been able to find a reason why my a alternator is only putting out 11.7 volts and wont go up. I got a new battery and a new alternator but even with the new one its still putting out 11.7.what could the problem be?
09-14-2012, 09:40 PM
That's a strange problem. Low voltage is usually due to a bad voltage regulator on the alternator. If you replaced it already it should be working. I suppose it's possible the new one you got is defective, but not likely. It's possible there is a problem with the wire harness that goes into the alternator, like a break in a wire or something. That is what controls the voltage regulator and tells it when to increase output. Check out the plug and wires that connect to the back. See if it looks dirty or corroded on the contacts or if there is any sign of melting on the wire loom or wires. You might need to get a multi-tester and check the continuity of the wires between the alternator and the computer.
09-15-2012, 03:45 PM
Thanks by anychance do you know what the volt meter should read if you test the plug that goes to the computer?
09-15-2012, 05:12 PM
Not sure what you mean there. System voltage should be in the high 13's to low 14's if everything is working properly. As for checking the plug, if you mean checking the continuity, there is no voltage reading on that. You aren't checking for voltage on that... the car should be off when you are doing that and you wouldn't have any power going to it.
If you have a multi-tester, there is normally a setting for the switch to test continuity. Basically all it does is send some power between the contacts to see if it has a closed circuit and power flows. You hook one lead from the tester to one wire on the plug at the alternator and hook the other lead to the opposite end of the same wire at the PCM. That's how you tell if the wire is good or if it has a break in it somewhere. You may need a wiring diagram and a long jumper wire with some alligator clips to do this, since you'll have to go from the engine bay to under the drivers side dash where the PCM is. Once both ends are hooked up you may want to try flexing or wiggling the wire harness a bit too, and see if the signal breaks up or resistance changes at all, as this could signal a break in the wire making intermittent contact... which could explain why it would have problems when cold but not after heating up, or why it might work and then suddenly die on you.
As you can tell, chasing down electrical gremlins can be a real pain in the you know what. Not my favorite thing to do by far.
09-15-2012, 06:44 PM
Would you happen to have a link to a diagram for the pcm pin location?
09-16-2012, 12:16 PM
Nope, no links. They aren't anywhere online that I know of, other than some diagnostics websites for mechanics that you have to pay for access to. It might be easier if I just scan the relevant pages from my manual and send them to you. If you want to shoot me a PM with your email addy I can send them to you in a pdf file.
Also, have you had the cars computer checked with a scanner for trouble codes (DTC's)? There are two related to generator performance. Also do you have a stereo system or other electrical accessories installed that might be creating extra draw on the system?
09-16-2012, 03:19 PM
Ok thanks for all the help, i fould that the red wire that pluges into the alt. Was pulled apart . i did find some info on the wire diagram ( http://www.justanswer.com/pontiac/3xhep-2004-pontiac-grand-does-not-crank-when-ignition-switch.html ) if u look almost all the way at the bottom u will c it. Im not realy sure what section to put that link but that could be very usefull for the form. But thanks for all your help again
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