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Alternator voltage drop

Ac on fans turn on voltage drop from 14.3 to 12.9 fans off 14.3 when fans on drops to 12.9 rev engine goes right back to 14.3

Posted by Anonymous on

3 Suggested Answers

6ya6ya
  • 2 Answers

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

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Posted on Jan 02, 2017

Ironfist109
  • 3018 Answers

SOURCE: I have a 2001 Jaguar

  • That has to be frustration. A couple things.

  1. First thing is are you using new OEM alternator? Or a rebuilt or re-manufactured alternator? There can be differences. I always recommend a new OEM rather than a rebuilt alternator when these issues arise. Just to get out of the way the quality of the alternator you are using now. Make sure that is not an issue.

  • It's obvious for some reason your cars charging is malfunctioning for some reason. Once you are sure that the alternator is good and is actually functioning properly then we look at why the voltage is dropping. You should have 14 Volts - 14.5 Volts at all times no matter what. When put under a load it may drop to 13 Vots or 12.5 Volts for just a couple seconds and then pop right back up to normal running voltage. So your alternator OR the charging system in general, for some reason, is not charging properly at all weather under a load or not.
  • An alternator MUST maintain an output of 13.8 Volts MINIMUM to charge the battery.

  1. First thing is to remove the serpentine belt and spin all the pulley and make sure they all turn free and with no hangups. If the alternators spinning is inhibited so to will the output to will be inhibited. All the pulleys should spin free but the crankshaft.

  1. Next I need you to check all the heavy wiring under the hood. Check the battery cable and clamps real good. These big cables often rot way inside and become defective and you would never know it unless you inspected them real well. Check connections at the alternator and starter too. The big black ground cables going to the block. Look them over real real well and feel for breaks and if needed splice them back and look for greening (oxidation) of the cables. make sure to re insulate any spliced wiring real well with electrical tape.

  1. Double check the battery again. If the battery has fallible ports the take a flat tool and carefully open the lids and fill with distilled water until full. Be real careful wihile doing this. Battery acid will eat anything including skin. Wash any off right away. Wear protective eye wear and gloves too when doing this.

  • One of the things that may be the cause after all this is checked is that the PCM does regulate the alternator on this vehicle. If all the things above I have listed bring no change then you will need to have the PCM diagnosed by a Jaguar dealer or specialist because your PCM could in fact be the problem.



  • Hope this helps and thank you for using FixYa.

Regards, Tony

Posted on Jul 29, 2011

  • 54 Answers

SOURCE: 2003 ford escape V6 idles 1000rpm, then drops over 5 seconds and then cycles back to 1000rpm...i recently had alternator replaced. I have regular oil changes. New gas filter. It sounds like something

A few things that could cause the problem are:1 Airflow meter that is if it is a fuel injected motor. 2 On carburettor models the idle solenoid will do that if it is faulty: 3 Airconditioning compressor or pump will click in and out with a sound causing the revs of the engine to alternate as it uses more or less energy accordingly. Also if the bearings in the compressor are worn in it's early stages of wear could make a similar sound to that of a fan: 4 The electric fan coming on too often because the engine is running very hot, could also cause the clicking sound as the thermostat clicks on and off. I suggest you check the water level in the bottle and in the radiator just to make sure that it's not getting too hot and if the levels are low then you have a problem that must be attended to immediately.

Posted on Apr 15, 2013

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1 Answer

Voltage drops when blower motor is turned on


Check the internal fuse of the blower ...this not on the main fuse panel...if you look underneath if the blower unit you will find the card fuse...it may be shorting or have water or corrosion on the pcb circuitry.clean or replace...if this does not cure it seems you have a slipping fan belt on the alternator or the alternator is starting to fail.

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Why does motor shut off when I turn on the heat and air?


Electrical issue. The heat or air draws more current and the electrical system probably drops voltage below the threshold the electronic control module can handle. First check that the Alternator is charging correctly. When running the system should have 13 to14.7 volts measured at the battery. If you turn on the heat/AC and it drops significantly you have a current draw issue (most likely bad fan motor, or short) If the voltage is below 13 volts when the car is running your alternator is likely bad.

Jan 26, 2016 | 2003 Isuzu Rodeo

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Voltage drops when setting still has new battery and alternator


Check grounds. Look at your cables. Could be corrosion.

Oct 30, 2015 | Cars & Trucks

1 Answer

2006 Cadillac CTS help My car was tested @auto zone for the batery n alternator n both passed Good voltage Everytime I go to crank my car it does not crank I have 2 jump it of even if it's for 15 mins


Luis: That makes no sense. But here is what others are saying: " How possible is it for a bad alternator to be tested good? I already had people telling me to replace it.

I got both the battery and alt tested. Both passed.

Reinstalled on the car and it ran good surprisingly after the battery was charged @ the autostore > till after about 10 minutes, then the battery meter dropped back down.

Soon as i turned on the lights/ac the battery meter dripped down real low. SOon as i turned them off the meter jumped back up.


Soon as i revved the engine the headlight would brighten then dim back down after the rev was over.

I can jump the car, but it will turn off by itself if you leave it idling to long then it needs another jump.
Driving it doesn't charge the battery up.. its actually drops the battery meter down more and more and more till its dead.

-Car doesn't drain the battery while its off.. so its nothing left on.


>> Now people are telling me there alternator was tested good, but the problems went away after buying a new alt.
"
Some people say there could be a loose belt not turning the alternator fast enough to supply power to lights/ac and charge battery. Or bad wires". or possibly a bad voltage regulator.

May 28, 2015 | 2006 Cadillac CTS

2 Answers

Voltage drop. When in parked I rev up the engine, when it comes down, the voltage drops from 14 to 10, for about 5 secs. I think the truck will cut off but it immediately comes back up to 14.


If the alternator is weak, and you have accessories like the headlights or blower motor running, and the RPM drops below 600, the voltage could be below 12. It would depend on the load, RPM, and several other factors.

Feb 12, 2014 | 2000 GMC Yukon XL

1 Answer

2003 ford escape V6 idles 1000rpm, then drops over 5 seconds and then cycles back to 1000rpm...i recently had alternator replaced. I have regular oil changes. New gas filter. It sounds like something...


A few things that could cause the problem are:1 Airflow meter that is if it is a fuel injected motor. 2 On carburettor models the idle solenoid will do that if it is faulty: 3 Airconditioning compressor or pump will click in and out with a sound causing the revs of the engine to alternate as it uses more or less energy accordingly. Also if the bearings in the compressor are worn in it's early stages of wear could make a similar sound to that of a fan: 4 The electric fan coming on too often because the engine is running very hot, could also cause the clicking sound as the thermostat clicks on and off. I suggest you check the water level in the bottle and in the radiator just to make sure that it's not getting too hot and if the levels are low then you have a problem that must be attended to immediately.

Apr 15, 2013 | Ford Escape Cars & Trucks

1 Answer

I have a 99 solara se. I have new battery and alternator but the car can't carry a load. Ac lights heater radio so forth


Not sure I follow your problem.
The alternator puts out 13-14 volts at idle but very few amps. If you turn on the headlights at idle the voltage may drop to 12 until you raise engine speed. The amperage goes up with engine speed.
Is the battery voltage at least 14 when the engine speed is 1500RPM or more ?

Jan 08, 2013 | 1999 Toyota Camry Solara

1 Answer

Compressor and fans do not turn on until rev engine


I passed this question the first time I read it, so I will take a stab at it now.
The fans don't come on until the compressor has pumped the freon pressure up to say 150 or 200 psi. And the compressor clutch has to have voltage to engage the clutch.
I wonder if the clutch is going and needs 14 volts instead of 12 to engage ? Or the relay that powers the clutch ?
Speeding up the engine would increase voltage from the alternator.
This is assuming the serpentine belt is tight and everything else is working correctly.
I think I would swap the relay with another and put a meter on that circuit to the ac clutch to see what it takes to engage it.

Jul 24, 2012 | 1992 Buick Regal

1 Answer

Shuts off when a/c,lights & radio are on like the alternater is bad but no engine code & batt & alt test fine


Hook up a volt meter and watch your voltage when sitting idle and at 2,000rpm while doing each of the following (separately). First turn on the lights, then AC with max fan speed, then wipers.

With a good alternator at idle, it should be around 14v. It should have minor drop with the lights and quickly get back to 14v, when the AC and wipers are turned on it may drop to 13.5v at the lowest.

With a bad alternator at idle, it will probably drop below 13.5v with just the lights, and below 12v with everything else.

At 1,800-2,000rpm there should be virtually no voltage drop more than 2-3secs for the ECU to compensate and command more power from the alternator as this is the peak operating RPM.

Jun 24, 2011 | 2004 Chevrolet TrailBlazer

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