My Alternator May Be Failing - 2nd Opinion Wanted

[RenegadeXR]

I'll describe the way my car has been behaving. I think it's an alternator issue, but if you have any other ideas, let me know:

In moderately warm weather (70° F) my DIC screen will sometimes very subtly pulse in brightness as the engine is running, sometimes almost too subtly to really notice. During colder weather (30° F), the interior and exterior lights of my car pulse lightly for the first few seconds until the car has been running a little while. However, while driving in colder weather, the DIC *and* driver side gauge cluster will continue to pulse in brightness very noticeably, almost to the point of completely turning and off. The overhead light will also pulsate if I have it switched on. The center console and 4-pack gages remain a steady brightness.

I originally thought it was a battery issue, but the car doesn't show any real issues during a cold crank when starting. Also, mashing the throttle can sometimes cause the DIC and driver-side gauge cluster to suddenly increase dramatically in brightness. This hints to me that the alternator isn't putting out a steady amount of power. Makes sense?

Also possibly worth noting -- I have the following electrical mods:

- DRL harness, with side marker turn signal modulation built in
- Technostalgia tail lamps — the ones that require a connection to the battery's positive terminal to operate. Although these are riddled with issues and requite frequent fixing, the issue happens even if I disconnect them from the positive battery post. I've even disconnected the entire rear factory electrical harness to completely disable them. No difference.
- LED front and rear side markers
- LED DRLs

That's really it. No aftermarket speakers or anything that should add any additional load.

[cajun1le]

I am not sure what kind of diagnostic tools are at your disposal but you can try the following:

-First, check the state of charge by using a DMM to measure the battery before starting the car (12.8V=fully charged, 12.6V=3/4 charged, 12.4V=1/2 charged and 12.2= 1/4 charged).
-Next if you have a fast DMM (a Fluke 87V or 88V), you can check output DC voltage and AC ripple while the engine is running. After startup the voltage can vary from 13.2-15.5VDC because the ECU reads the battery's state of charge and adjusts the field voltage accordingly. The AC ripple should not exceed .5V and it is measured at the alternator battery terminal (requires a fast DMM for accurate reads and checks the diode bridge on the alternator).
-Load test the battery.

[RenegadeXR]

Thanks. I had the battery load tested at Pep Boys (I know, not the best place) last year and the battery was fine. I'm thinking I'll just take it into my local dealership. They've done a good job in the past diagnosing weird issues that were hard to pin down. I have a multimeter, but regardless of what I find, I wouldn't have the expertise to fix it myself.

[MLL67RSSS]

A member NFERNOSS posted this excellent description of the Camaro's charging system in another thread. The brightness of the gauges would be limited by how much voltage there is, the "generator" as they call it does the voltage regulation I believe so that may be the issue. Maybe seeing the brightness "pulse" with the charging current pulses if the voltage isn't being properly regulated. Also I see you had your battery load tested a year ago, if it was borderline may have "gone south" over the last year and may suck up a lot of current at first pulling the voltage down a bit between current pulses.

Originally Posted by NFERNOSS

This may be way more info than I need to share, or for "some" to even comprehend. But, this is how the system works, and any needle fluctuation is normal. Trust me, when there is an issue, the idiot lights and DIC messages will let ya know.



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.

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 more 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.

© 2012 General Motors. All rights reserved.

[RenegadeXR]

Thanks a lot. I will try to read that over a bit. It could still be the battery then, since it could be sucking power from the alternator periodically. This morning, my car really struggled to crank. Actually, the electronic starter kind of ticked lightly the first few times, and on the 3rd try or so, I could hear it actually crank the pistons around. Then it fired up.

Normal startup is 3 cranks, then engine fires.

This morning was: 2 light ticks (maybe a very very weak crank?), 3 cranks, then engine fires.

[mar10]

This sounds like the same issue I am having with my 07 Tahoe. But the headlights pulse noticeably with no correlation to throttle/ rpms. I took it to a mechanic friend at work that hooked it up to a snap on machine similar to the ones used by auto store for quick diagnostics and it said both battery and alternator were good. Then he hooked it up to a machine that can apply a load to test the alternator (The tool/ machine was on a cart and similar to the one that's in the link im going to post further down). The alternator appeared to be slightly dropping in voltage at idle. He said it should be at 14.6 but was reading 14.0. Then he applied a "load" to it and he said the voltage would fluctuate and the battery was not taking a charge like it should (or something like that. This is my recollection of the dumbed down information he relayed to me.) He said it could be either the alternator or battery but was 70%-80% sure it was the alternator.

This is a widespread issue with tahoes and seems to be hard to diagnose because initial testing shows that both are good and people don't pay to have it diagnosed further and or some dealers / mechanics just start throwing parts at it. I searched and searched wanting a definite answer but couldn't find anything solid. The best answers were it might be the alternator, then second was it might be the battery, third was it might be a bad ground or weak wiring. The solutions for the first two were straight forward replace alternator or battery for some people this worked but not always. The third the solution was a "Big 3 Wire Mod". Basically that's replacing the main wires of the charger system with larger/ lower gauge wires but there was no solid proof that it fixed the issue every time. So I had a list of stuff to try somewhat blindly.

I tried to prioritize what I was going to do based on the findings above and did a little more research and the route Im going to take is the alternator, battery then check into the ground connection possibly replace wires. But I did find this page ( http://www.sparkys-answers.com/2012/...licker-or.html ) that pointed to it being the alternator. I had my mechanic friend look at it and he said that aside from the heat test the guy did my Tahoe was showing the same symptoms. My mechanic friend said that the heat could be caused by a bunch of other issues and the guy whom typed up the information even noted that. So I ordered an alternator and it should arrive tomorrow. Ill try to remember to let you know if this fixes the lights pulsating and flickering in my Tahoe after I get it installed.

[mar10]

Originally Posted by mar10

This sounds like the same issue I am having with my 07 Tahoe. But the headlights pulse noticeably with no correlation to throttle/ rpms. I took it to a mechanic friend at work that hooked it up to a snap on machine similar to the ones used by auto store for quick diagnostics and it said both battery and alternator were good. Then he hooked it up to a machine that can apply a load to test the alternator (The tool/ machine was on a cart and similar to the one that's in the link im going to post further down). The alternator appeared to be slightly dropping in voltage at idle. He said it should be at 14.6 but was reading 14.0. Then he applied a "load" to it and he said the voltage would fluctuate and the battery was not taking a charge like it should (or something like that. This is my recollection of the dumbed down information he relayed to me.) He said it could be either the alternator or battery but was 70%-80% sure it was the alternator.

This is a widespread issue with tahoes and seems to be hard to diagnose because initial testing shows that both are good and people don't pay to have it diagnosed further and or some dealers / mechanics just start throwing parts at it. I searched and searched wanting a definite answer but couldn't find anything solid. The best answers were it might be the alternator, then second was it might be the battery, third was it might be a bad ground or weak wiring. The solutions for the first two were straight forward replace alternator or battery for some people this worked but not always. The third the solution was a "Big 3 Wire Mod". Basically that's replacing the main wires of the charger system with larger/ lower gauge wires but there was no solid proof that it fixed the issue every time. So I had a list of stuff to try somewhat blindly.

I tried to prioritize what I was going to do based on the findings above and did a little more research and the route Im going to take is the alternator, battery then check into the ground connection possibly replace wires. But I did find this page ( http://www.sparkys-answers.com/2012/...licker-or.html ) that pointed to it being the alternator. I had my mechanic friend look at it and he said that aside from the heat test the guy did my Tahoe was showing the same symptoms. My mechanic friend said that the heat could be caused by a bunch of other issues and the guy whom typed up the information even noted that. So I ordered an alternator and it should arrive tomorrow. Ill try to remember to let you know if this fixes the lights pulsating and flickering in my Tahoe after I get it installed.

I installed the new alternator in my Tahoe last night. Took about 15 min. All the flickering in the lights has stopped. I turned the heater fan up, the rear defrost on, the radio, DVD player, brights Ave all interior lights and there was no flickering or pulsing of the lights. I didn't take it out to drive but I'll let you know if there is any difference.

[RenegadeXR]

Today, while I was actually pretty far away from my home, my car failed to start up. I ticked (no cranking) a few times and gave up. I tried again, and it reluctantly started. Stabilitrack warnings popped up (it seems for w/e reason, Stabilitrack is the first system to report failure if theres another issue lol), the dashboard lit up but the speedo and tach stayed stationary, and every single light on the cluster lit up at once (traction control off, etc.) Pretty much everything except the check engine light. My guess this was a side effect of a false positive for "stabilitrack failure".

I made an emergency run to a Chevy dealership but their service department closed. Some guy who usually just handles appointments offered to test the battery for me, claimed the battery was fine with a load test, and they said it could be "something causing load on the system." They offered to install a battery when a first puled in, but that offer sort of went to the wayside after the test because they didn't want to charge me for something I might not need. I was honestly dealing with people not trained to diagnose this stuff, but props to them for trying late on a Saturday.

I cranked the car, barely started it, and headed home with a business card in hand for a towing company recommended by the dealership. I did a few cranks in a row when I got back home, found that the starter is very inconsistent. Sometimes it cranks normally, but most of the time it just ticks. I hooked my battery to a Battery Tender, and it indicates the battery is very low, so I'm letting it charge overnight. Not sure why the low charge wasn't mentioned at the dealership, but again, I was likely asking for help from the wrong people.

At this point, I'd like to ditch the stock battery regardless since it's 5 years old, and there are much nicer aftermarket options that open the door to upgrades for other things down the road.

If the battery swap makes no difference, I am going to get it serviced again. This has been going on for 2 years but to a milder extent until recently, and I'm getting fed up guessing what the problem is.

[spadz93]

Not trying to thread-jack, but I'm on a year-old interstate megatron plus battery and a brand new alternator, and still get rough starts if i let the car sit for two days. Wondering if my old, weak alternator took out the battery for the time it was in there before being replaced?

[RenegadeXR]

I hooked up a battery tender jr trickle charger. The status LED is still solid red 12 hours latter, meaning the battery is below 80% and not fully taking a charge. However, the engine starts on a dime now. I guess I'll be hooking it up to the tender each night for now until Amazon has a ACDelco 94RAGM back in stock. I'll swap it myself and go from there.

Update: About 14 hours after hooking up the battery tender, it's now flashing green meaning the battery has at least 80% charge to be driven normally. I'll wait until it's completely charged, but now I am wondering: A) Why was it so low on charge? B) Was I driving it enough to recharge the battery? C) Is the alternator charging it properly? D) Is the battery recharging at a much slower rate than what's considered normal? E) Is the parasitic drain from my aftermarket tail lamps (which connect to the positive battery terminal) overcoming the normal rate of charge?

I had let the car sit for 2 weeks during Christmas, although it had no problems starting when I got back. I then daily drove it for about 15 minutes to work and 15 minutes back for 5 days in a row, without much other driving. Maybe that wasn't enough to put it back in a normal state, especially since those Technostalgia tail lamps may be causing parasitic drain between drives? A lot of people with those model tail lamps suggest topping off the battery regularly to be safe. Maybe I just need to make this a monthly ritual, and I had a false expectation that 30 minutes total daily driving for a week would've been enough to fully recharge it.

[speedygonzales]

Johnson Controls makes the vast majority of batteries sold including your AC Delco, Optima and Interstate. If you're buying one of their 'branded" batteries like AC Delco, you're wasting a lot of money. Do yourself a favor and go to local retailer and get you an Interstate battery. Not only will you get a product that does NOT have shipping damage, you have a place to go to if it has a problem later. Knowing this, I have used Interstate for years and never had a problem. If they won't price match, it's worth it to pay a few dollars more for it.

[RenegadeXR]

So I just let the battery tender reach full charge (solid green), took the car down some winding country roads that i like. Spent about an hour on that. Gased the car up. Started it multiple times during the day. The car cranks quicker than it'd ever before (only 2 cranks and it fires), and the pulsating dashboard issue is fixed.

However, when I hooked the battery tender up, it's solid red again (< 80% charge.) Per the document NFERNOSS wrote up, the battery should charge automatically if it drops below 80%. So something is still messed up, I'll swap the battery and go from there.

[102SS]

Originally Posted by RenegadeXR

I'll describe the way my car has been behaving. I think it's an alternator issue, but if you have any other ideas, let me know:

In moderately warm weather (70° F) my DIC screen will sometimes very subtly pulse in brightness as the engine is running, sometimes almost too subtly to really notice. During colder weather (30° F), the interior and exterior lights of my car pulse lightly for the first few seconds until the car has been running a little while. However, while driving in colder weather, the DIC *and* driver side gauge cluster will continue to pulse in brightness very noticeably, almost to the point of completely turning and off. The overhead light will also pulsate if I have it switched on. The center console and 4-pack gages remain a steady brightness.

I originally thought it was a battery issue, but the car doesn't show any real issues during a cold crank when starting. Also, mashing the throttle can sometimes cause the DIC and driver-side gauge cluster to suddenly increase dramatically in brightness. This hints to me that the alternator isn't putting out a steady amount of power. Makes sense?

Also possibly worth noting -- I have the following electrical mods:

- DRL harness, with side marker turn signal modulation built in
- Technostalgia tail lamps — the ones that require a connection to the battery's positive terminal to operate. Although these are riddled with issues and requite frequent fixing, the issue happens even if I disconnect them from the positive battery post. I've even disconnected the entire rear factory electrical harness to completely disable them. No difference.
- LED front and rear side markers
- LED DRLs

That's really it. No aftermarket speakers or anything that should add any additional load.

Mine does that once in a while too.

Car seems fine, volts are good so I am not to concerned.

[mar10]

Originally Posted by RenegadeXR

I hooked up a battery tender jr trickle charger. The status LED is still solid red 12 hours latter, meaning the battery is below 80% and not fully taking a charge. However, the engine starts on a dime now. I guess I'll be hooking it up to the tender each night for now until Amazon has a ACDelco 94RAGM back in stock. I'll swap it myself and go from there.

Update: About 14 hours after hooking up the battery tender, it's now flashing green meaning the battery has at least 80% charge to be driven normally. I'll wait until it's completely charged, but now I am wondering: A) Why was it so low on charge? B) Was I driving it enough to recharge the battery? C) Is the alternator charging it properly? D) Is the battery recharging at a much slower rate than what's considered normal? E) Is the parasitic drain from my aftermarket tail lamps (which connect to the positive battery terminal) overcoming the normal rate of charge?

I had let the car sit for 2 weeks during Christmas, although it had no problems starting when I got back. I then daily drove it for about 15 minutes to work and 15 minutes back for 5 days in a row, without much other driving. Maybe that wasn't enough to put it back in a normal state, especially since those Technostalgia tail lamps may be causing parasitic drain between drives? A lot of people with those model tail lamps suggest topping off the battery regularly to be safe. Maybe I just need to make this a monthly ritual, and I had a false expectation that 30 minutes total daily driving for a week would've been enough to fully recharge it.

Sounds like you need to get the battery and alternator tested by someone that knows what they are doing.