# Battery or Alternator



## Bud9051 (Nov 11, 2015)

If it is the original battery it is due regardless, but it does sound like it isn't charging. You could leave the headlights on for awhile to see if the battery holds well or drops fast. Then, if the reading is say 11 volts see if the alternator tries to bring it up.

Bud


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## JBG420 (Aug 27, 2011)

The battery is less than 3 years old.


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## ZZZZZ (Oct 1, 2014)

Don't know if 06 Jeeps have a separate voltage regulator component or if it's integrated into the alternator itself. Check that.
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## JBG420 (Aug 27, 2011)

Internal voltage regulator.
It's got to be the alt right? With the dash light coming on and a dead battery within 24 hours. Cables all good a tight, grounds good, no corrosion.


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## ZZZZZ (Oct 1, 2014)

I have a 99 Mitsubishi Montero Sport, coming up on 200,000 miles. Its alternator also died at about 165,000 mile. (That and a leaky radiator are the only things I've had to replace.)
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## Brainbucket (Mar 30, 2015)

Alternator is not charging. Check to see if you have power on the big wire on alternator. If it is computer controlled, you can't test it. If not, There should be a key on power going to the regulator and if it's 2 wire connector, the other side should have power all the time. But I believe it's computer controlled. Get a good alternator, not auto zone unless you want to do it again and again and again and then thinking since I put 3 alternators on here and it's still not working, it must be something else. Then the real trouble starts. You then start replacing good parts with bad. I like NAPA.:vs_cool:


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## JBG420 (Aug 27, 2011)

Yea I prefer NAPA myself but will likely do a remanufactured alt. I don't plan to be driving this jeep more than 6-12 months. But even these 160amp reman alts are close to $300. Just don't want to waste time/money if it could be something else.


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## mark sr (Jun 13, 2017)

You could always have the alternator tested. Most parts stores will test it for free.


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## ZZZZZ (Oct 1, 2014)

mark sr said:


> You could always have the alternator tested. Most parts stores will test it for free.


Yeah, most of them will just hook up the voltage meter with the engine running and tell you under 13v, it must be bad. And by the way, we have a replacement for you in stock and it just happens to be on sale this week. You're in luck! :biggrin2:
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## Nealtw (Jun 22, 2017)

In the old days you just disconnected the battery when the engine was running. 
If the engine stopped it was a generator or alternator problem. If it is still running you can measure what voltage it is producing.


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## JBG420 (Aug 27, 2011)

Yea I've used the disconnect one cable while running on older cars but with all the electronics in today's car just asking for trouble doing that (imo).

I'm pretty convinced it's the alt. With the voltage regulators when running, should be well above 14v to charge the battery. I'm getting a drop from 12.7v (car off) to 12.0-12.1v. The battery light came on 2 days ago. All cables are nice and tight and no corrosion. And corrosion on the alt battery connector and less than 3 year old battery. Has to be the alternator. Ordered a remfg one from Napa and will install it later.


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## Brainbucket (Mar 30, 2015)

Nealtw said:


> In the old days you just disconnected the battery when the engine was running.
> If the engine stopped it was a generator or alternator problem. If it is still running you can measure what voltage it is producing.


You can do that with generators, not alternators. It hurts them bad. With generators, you can start the vehicle and yank the battery out and go. With alternators, they need the battery to work correctly.:vs_cool:


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## Nealtw (Jun 22, 2017)

Brainbucket said:


> You can do that with generators, not alternators. It hurts them bad. With generators, you can start the vehicle and yank the battery out and go. With alternators, they need the battery to work correctly.:vs_cool:


Now that you say it, I do remember that. It was a long time ago.:biggrin2:


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## Bud9051 (Nov 11, 2015)

A tight connection isn't always making good contact. I've had a thin layer of corrosion cause problems. When reading the voltage drop check at the terminal and then the wire to see if both read the same.

Bud


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## mark sr (Jun 13, 2017)

> I'm pretty convinced it's the alt


Then take it off but have them test the alternator first before they sell you a replacement.


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## Oso954 (Jun 23, 2012)

I'd take it to a mechanic that can read the PCM codes.
The alternator is controlled by the PCM, not a regulator.


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## Bigplanz (Apr 10, 2009)

I helped a friend with her Suburu's alternator a few years ago. It wasn't putting out anything. The readings were the same as yours. With the engine running, a meter should show at least 13.5V at idle, if not the alternator is either bad or there is a break in the electrical circuit. Below is a fuseable link test. When I checked her car, I did this test and there was continuity between the alternator and the battery, so I knew the alternator was bad. Went to the salvage yard, bought one for 15 bucks and it worked. Still working, as far as i know. Alternator on the Outback was easy. Right in front, right on top. Don't know where yours is but some are buried deep.

http://easyautodiagnostics.com/misc-index/how-to-test-a-bad-alternator-2


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## mark sr (Jun 13, 2017)

ZZZZZ said:


> Yeah, most of them will just hook up the voltage meter with the engine running and tell you under 13v, it must be bad. And by the way, we have a replacement for you in stock and it just happens to be on sale this week. You're in luck! :biggrin2:
> .
> .


 I meant - remove the alternator and have it bench tested. If he's convinced it's the alternator and you generally need to turn in the core - to me it's a no brainer to remove the alt and have them bench test it before buying a replacement.


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## bfletcher7 (Jan 16, 2016)

I'm sure this is resolved now and I'm not a mechanic but when I've troubleshooted a battery/alternator issue I first checked for 12.x volts across the battery. If that condition was met I'd have someone start the car and take it up to 2,000 RPM and if the voltage jumped to 13.x I assumed the alternator was good. Is this not valid?


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## Bigplanz (Apr 10, 2009)

bfletcher7 said:


> I'm sure this is resolved now and I'm not a mechanic but when I've troubleshooted a battery/alternator issue I first checked for 12.x volts across the battery. If that condition was met I'd have someone start the car and take it up to 2,000 RPM and if the voltage jumped to 13.x I assumed the alternator was good. Is this not valid?


At 2000 rpm it should be more in the14V range.


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## JBG420 (Aug 27, 2011)

Yep definitely the alternator in my case. Even without reving just at idle a working alternator should be putting out over 13 volts.


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## Bigplanz (Apr 10, 2009)

JBG420 said:


> Yep definitely the alternator in my case. Even without reving just at idle a working alternator should be putting out over 13 volts.


My Navigator puts out between 13.6 and 14.1 at idle, except when the air suspension compressor comes on, then it drops to 12.9 or so. This is only for a few seconds. Once the compressor goes off, the voltage goes back to the high 13, low 14V range. Even with the AC on, the voltage doesn't vary much. I think the computer compensates by increasing engine RPM at idle to keep the voltage steady.


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## Brainbucket (Mar 30, 2015)

I have a 2011 Chevy Traverse. It sometimes will go down to 12.8 volt and I'm driving. The PCM, Powertrain Control Module, regulates the alternator. It has decided that it doen't need to charge it at that time. Here is the theory; 
*Charging System Description and Operation*

*Electrical Power Management Overview*

The electrical power management system is designed to monitor and control the charging system and send diagnostic messages to alert the driver of possible problems with the battery and generator. This electrical power management system primarily utilizes existing on-board computer capability to maximize the effectiveness of the generator, to manage the load, improve battery state-of-charge and life, and minimize the system's impact on fuel economy. The electrical power management system performs 3 functions:


It monitors the battery voltage and estimates the battery condition.
It takes corrective actions by boosting idle speeds, and adjusting the regulated voltage.
It performs diagnostics and driver notification.
 The battery condition is estimated during ignition-off and during ignition-on. During ignition-off the state-of-charge of the battery is determined by measuring the open-circuit voltage. The state-of-charge is a function of the acid concentration and the internal resistance of the battery, and is estimated by reading the battery open circuit voltage when the battery has been at rest for several hours.
The state-of-charge can be used as a diagnostic tool to tell the customer or the dealer the condition of the battery. Throughout ignition-on, the algorithm continuously estimates state-of-charge based on adjusted net amp hours, battery capacity, initial state-of-charge, and temperature.
While running, the battery degree of discharge is primarily determined by a battery current sensor, which is integrated to obtain net amp hours.
In addition, the electrical power management function is designed to perform regulated voltage control to improve battery state-of-charge, battery life, and fuel economy. This is accomplished by using knowledge of the battery state-of-charge and temperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.
The Charging System Description and Operation is divided into 3 sections. The first section describes the charging system components and their integration into the electrical power management. The second section describes charging system operation. The third section describes the instrument panel cluster operation of the charge indicator, driver information center messages, and voltmeter operation.
*Charging System Components*


*Generator*

The generator is a serviceable component. If there is a diagnosed failure of the generator it must be replaced as an assembly. The engine drive belt drives the generator. When the rotor is spun it induces an alternating current (AC) into the stator windings. The AC voltage is then sent through a series of diodes for rectification. The rectified voltage has been converted into a direct current (DC) for use by the vehicles electrical system to maintain electrical loads and the battery charge. The voltage regulator integral to the generator controls the output of the generator. It is not serviceable. The voltage regulator controls the amount of current provided to the rotor. If the generator has field control circuit failure, the generator defaults to an output voltage of 13.8 V.

*Body Control Module (BCM)*

The body control module (BCM) is a GMLAN device. It communicates with the engine control module (ECM) and the instrument panel cluster for electrical power management (electrical power management) operation. The BCM determines the output of the generator and sends the information to the ECM for control of the generator turn on signal circuit. It monitors the generator field duty cycle signal circuit information sent from the ECM for control of the generator. It monitors a battery current sensor, the battery positive voltage circuit, and estimated battery temperature to determine battery state of charge. The BCM performs idle boost.

*Battery Current Sensor*

The battery current sensor is a serviceable component that is connected to the negative battery cable at the battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the battery current. It directly inputs to the BCM. It creates a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0–100 percent. Normal duty cycle is between 5–95 percent. Between 0–5 percent and 95–100 percent are for diagnostic purposes.

*Engine Control Module (ECM)*

When the engine is running, the generator turn-on signal is sent to the generator from the ECM, turning on the regulator. The generator's 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 duty terminal is connected internally to the voltage regulator and externally to the ECM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the ECM that a problem exists. The ECM monitors the generator field duty cycle signal circuit, and receives control decisions based on information from the BCM.

*Instrument Panel Cluster*

The instrument panel cluster provides the customer notification in case a concern with the charging system. There are 2 means of notification, a charge indicator and a driver information center message of SERVICE BATTERY CHARGING SYSTEM if equipped.
*Charging System Operation*

The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:


Battery Sulfation Mode
Charge Mode
Fuel Economy Mode
Headlamp Mode
Start Up Mode
Voltage Reduction Mode
 The engine control module (ECM) controls the generator through the generator turn ON signal circuit. The ECM monitors the generator performance though the generator field duty cycle signal circuit. The signal is a pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0–100 percent. Normal duty cycle is between 5–95 percent. Between 0–5 percent and 95–100 percent are for diagnostic purposes. The following table shows the commanded duty cycle and output voltage of the generator:

Commanded Duty Cycle
Generator Output Voltage
10%
11 V
20%
11.56 V
30%
12.12 V
40%
12.68 V
50%
13.25 V
60%
13.81 V
70%
14.37 V
80%
14.94 V
90%
15.5 V
The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is PWM signal of 128 Hz with a duty cycle of 0–100 percent. Normal duty cycle is between 5–99 percent. Between 0–5 percent and 100 percent are for diagnostic purposes.


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## Brainbucket (Mar 30, 2015)

*Battery Sulfation Mode*

The BCM will enter this mode when the interpreted generator output voltage is less than 13.2 V for 45 minutes. When this condition exists the BCM will enter Charge Mode for 2–3 minutes. The BCM will then determine which mode to enter depending on voltage requirements.
*Charge Mode*

The BCM will enter Charge Mode when ever one of the following conditions are met.


The wipers are ON for than 3 seconds.
GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.
The estimated battery temperature is less than 0°C (32°F).
Battery State of Charge is less than 80 percent.
Vehicle speed is greater than 145 km/h (90 mph)
Current sensor fault exists.
System voltage was determined to be below 12.56 V
 When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9–15.5 V, depending on the battery state of charge and estimated battery temperature.
*Fuel Economy Mode*

The BCM will enter Fuel Economy Mode when the estimated battery temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 amperes and greater than -8 amperes, and the battery state-of-charge is greater than or equal to 80 percent. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5–13.1 V. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.
*Headlamp Mode*

The BCM will enter Headlamp Mode when ever the headlamps are ON (high or low beams). Voltage will be regulated between 13.9–14.5 V.
*Start Up Mode*

When the engine is started the BCM sets a targeted generator output voltage of 14.5 V for 30 seconds.
*Voltage Reduction Mode*

The BCM will enter Voltage Reduction Mode when the calculated ambient air temperature is above 0°C (32°F). The calculated battery current is less than 1 ampere and greater than -7 amperes, and the generator field duty cycle is less than 99 percent. Its targeted generator output voltage is 12.9 V. The BCM will exit this mode once the criteria are met for Charge Mode.
*Instrument Panel Cluster Operation*


*Charge Indicator Operation*

The instrument panel cluster illuminates the charge indicator and displays a warning message in the driver information center if equipped, when the one or more of the following occurs:



The engine control module (ECM) detects that the generator output is less than 11 V or greater than 16 V. The instrument panel cluster receives a GMLAN message from the ECM requesting illumination.
The instrument panel cluster determines that the system voltage is less than 11 V or greater than 16 V for more than 30 seconds. The instrument panel cluster receives a GMLAN message from the body control module (BCM) indicating there is a system voltage range concern.
The instrument panel cluster performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.
 
*Display Message: BATTERY NOT CHARGING SERVICE CHARGING SYSTEM or SERVICE BATTERY CHARGING SYSTEM*

The BCM and the ECM will send a serial data message to the driver information center for the BATTERY NOT CHARGING SERVICE CHARGING SYSTEM or SERVICE BATTERY CHARGING SYSTEM message to be displayed. It is commanded ON when a charging system DTC is a current DTC. The message is turned OFF when the conditions for clearing the DTC have been met.:vs_cool:


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## alex6999 (Nov 11, 2017)

Just use clamp amperage meter over cable to battery, first when engine not running - it should be positive(discharging) and when running - negative(charging) or vice versa.



Nealtw said:


> In the old days you just disconnected the battery when the engine was running.


never do it at modern cars, you can kill ECU. Or maybe even half of modules.


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