Question about 2002 GMC Sierra 1500

2 Answers

Alternator puts out about 16 volts, boils battery. is this an internaly regulated alternator , can output be adjusted

Posted by on


2 Answers

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that got 5 achievements.


    An expert who has answered 20 or more questions within one hour.


    An expert who has answered 20 questions.

  • Expert
  • 90 Answers

Internal regulator neads to be replaced, or replace the alternator

Posted on Sep 29, 2010

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • GMC Master
  • 8,836 Answers

Regulator is integral to the generator:
reg is solid state--no adjustment

alternator puts out about 16 volts, boils battery. - ee195d8.gif

Posted on Sep 29, 2010


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Good luck!

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Hi I recently washed my ba falcon and now my ABS lights are on and my battery boiled, i think my battery is over charging? any idea what it mite be?

battery boiling indicates that the voltage regulator is faulty and not regulating the alternator output to 14.5-14.8 volts
if that unit is part of the alternator and you sprayed water into the alternator ,that regulator if internal would have shorted out
the ABS problem could be from water in the harness connections
take it to an auto electrician and have the charge system fully checked out

Apr 12, 2018 | Cars & Trucks

1 Answer

My battery light came on while i was driving than a few minutes later everything shut off. The battery was replaced in january and alternator was replaced in october.. what could be the problem?

For the alternator to work B+ voltage must be applied to the heavier gage wire on the back of the alternator ,plus the alternator is computer controlled , by the PCM !
Charging System Indicators
BATTERY The IPC illuminates the battery indicator when the following occurs:
The PCM detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the PCM requesting illumination.

The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the body control module (BCM) indicating the system voltage.

The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

The ignition is on, with the engine off.
BATTERY NOT CHARGING The IPC illuminates the battery not charging indicator in the driver information center when the following occurs:
The PCM detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the PCM requesting illumination.

The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the body control module (BCM) indicating the system voltage.

Your best is to have a qualified repair shop check it out ! Could have DTC'S - diagnostic trouble codes stored !
DTC P0562
The powertrain control module (PCM) continuously monitors that the system voltage stays within the proper range. If the PCM detects an excessively high system voltage, DTC P0563 will set. A high voltage condition may cause a stalling condition or other drive ability concerns.
DTC P0621
The powertrain control module (PCM) uses the generator turn on signal circuit to control the generator. A high side driver within the PCM allows the PCM to turn the generator ON and OFF. When Generator operation is desired, the PCM sends a 5 volt signal to the voltage regulator via the generator turn on signal circuit. This causes the voltage regulator to begin controlling the generator field circuit. Once the Generator is enabled by the PCM, the voltage regulator controls generator output independently of the PCM. Under certain operating conditions, the PCM can turn Off the generator by turning Off the 5 volt signal on the generator turn on signal circuit. The PCM has fault detection circuitry which monitors the state of the generator turn on signal circuit. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the generator turn on signal circuit, pulling the voltage low. This also causes the PCM to set the DTC.
DTC P0622
Checking for codes an voltage drop testing the connections an using a scan tool to check data parameters is the only way to solve your problem . Which means taking to a qualified repair shop !

Jul 26, 2016 | 2002 GMC Envoy

1 Answer

I have holden jackaroo 1996 check trans light comes on and flash ...and the battery volt indicator goes from around 12 up to 16 when it flashes and lose power. .. help please...

check the output of the alternator as the regulator should be set at 14.5 volts max 16 volts is way to much for the electronics and amounts to a power surge.

Dec 25, 2014 | Cars & Trucks

1 Answer

Low voltage

youre alt is internaly regulated so with it being new and youre battery is new follow youre wiers from youre alt to youre firewall making sure you dont have any bare wiers cuasing the system to have a week short and make sure all of youre conections from youre battery to youre starter and the alternator are cleane!

Jan 12, 2013 | 1988 GMC K2500

1 Answer

Running voltage is 16 volts. is this to high, poss alternator?

Your voltage regulator should start backing off the charge rate when it gets to 14.5 or so volts,so i would advise you to either replace the regulator [which is in the alternator] or the alternator it's self.A charge rate that maintains 16 volts will boil your battery dry and ruin it and also the acid that boils out of it will remove paint,rot hoses,ruin wiring etc. so do it soon.Hope this helps!

Jan 08, 2010 | 2002 Mercedes-Benz C-Class

3 Answers

Same symptoms, sulfur smell + battery problems on 2001 Durango

possible voltage regulator is faulty (in the alternator) and boiling the battery. Since the battery has sulphuric acid in it, that would give you the sulpher smell. Get your mechanic to test the voltage/amps output from the alternator.

Oct 03, 2009 | 2001 Dodge Durango

2 Answers

Battery voltage is very high when driving over 14

Voltage regulator is going bad. Have alternator tested or go ahead and have it replaced. Also this would be a good time to have the battery tested. Usually an alternator that is over charging will "cook" the battery causing it to not charge, not hold a charge, to losing the gel/electrolyte solution due to boil out.

Jul 17, 2009 | 2002 Audi A4

1 Answer

Volt meter in s reading almost 16 volts

Your voltage regulator needs to be adjusted to 14.5 volts or if it won't adjust you need to replace the regulator. If you have a bad ground it could make the alternator see the wrong voltage and cause it to go to full charge. If it haas a built in regulator you can buy it at an alternator shop and replace it it is help in place by screws. It would be helpful if you tell us what year and make of car. Some put out as much as 26 volts. so more input is better, also please rate this if you need more help.

Jul 15, 2009 | 1987 Nissan King Cab

1 Answer

98 ford windstar has battery light on put new battery in and its still on. I put volt meter on battery while car is running and its reading 16 volts

The problem is the voltage regulator is bad. However the regulator is almost as expensive as a rebuilt alternator so unless the alternator as been replaced recently I would suggest to go with the rebuilt alternator.

Mar 03, 2009 | 1996 Ford Windstar

1 Answer

Alternator when warm over charges 16 17 volts is regulator inside

are you boiling your battery?
are you having starting problem?
a shorted battery will cause you alt to charge very hard.

Sep 24, 2008 | 1988 Volkswagen Fox

Not finding what you are looking for?
Cars & Trucks Logo

121 people viewed this question

Ask a Question

Usually answered in minutes!

Top GMC Experts


Level 3 Expert

79186 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22326 Answers

Ronny Bennett Sr.
Ronny Bennett Sr.

Level 3 Expert

6927 Answers

Are you a GMC Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides