2013 Sliverado

[Tim Twite]

I have a 2013 1500 LTZ. It shows around 14 volts on the meter some times less. A few days ago it started running in about the middle of the shaded scale above 14 so my guess 15 to 16 volts all the time.  I replace the battery thinking it was 7 years old and temps were cold might be getting weak.  That made no difference still the same.  When the head lights are on it goes down to just above 14 and as I have read it should be 14.5 when head lights are on.  I do not get any warnings or error messages and everything seems to work fine but am concerned it is over charging.  I took a road trip yesterday and was watching as I drove average speed 75 in a 2 1/2 hour trip a couple of times it went down to just below 14 and stayed there for a few minutes and then climbed right back up and stayed there.  any ideas what is going on or should be checked??

[davester]

Put a voltmeter cross the battery with the engine running and see what the voltage is.  It should be 14V +- .5V.  Much past that, either way, indicates a charging problem, possibly with the alternator, or possibly with the wiring/connectors, or possibly with one of the computers (as a computer controls how much power the alternator is commanded to put out).

[Doug_Scott]

Gauge in the dash is just an indicator.  Now I am not saying that current in dash gauges are the same now as they used to be, but, at one time a customer came in with his Japanese made car, I forget the brand, but for this it really does not matter.  He was complaining of very  low oil pressure when he started his car after it sat for many hours.  It was in the middle of winter at the time.  Tested the oil pressure when it was hot, gauge showed it in the middle of the sweep, pressure measured good as well.  Left the car in the shop over night, with gauge attached, and next morning got good pressure.  Put the sender back in, in dash gauge showed the same as the day before, in the middle of the sweep.  I put the car outside and went on to other jobs.  The customer came to get his car at end of day and he started the car up out on the lot and started honking his horn to get my attention.  He told me that the gauge was showing near 0 psi oil pressure.  I went out with the mechanical gauge, put it on the engine, and it showed 45psi, same as that morning.  He left the car again so I could pull the dash apart and see if I could find something in the gauge or wiring.  I pulled the gauge out the next morning and took the cover off of it.  All it was inside was a bi-metallic spring and some resistors.  The problem was the current going through the bi-metallic spring was not enough to heat up the spring to move the needle.  After the interior warmed up it would work fine again.  Leaving the car in the shop left it warn enough in the morning to work properly.  His coolant temp gauge did the same thing, but, it was normal for an engine to take longer to warm up in the winter. 

[CamGTP]

No warnings, no problem to me. As said the computer is controlling the voltage output of the alternator. 13-15 volts is going to be considered normal.

 

If anything you could go around and remove/clean all battery grounds, engine ground and connecting points at the starter/alternator.

[Jsdirt]

What Cameron said. This is a post that's been popping up ever since the first GMT-900's rolled out in 2007. Do a search - there's several threads on this topic.

 

The long and short of it is, the system is PCM duty-cycle controlled. Sometimes it will charge - sometimes it won't. All demand-based. This was GM's brainstorm to squeeze another .0001 MPG out of these trucks, in addition to the failure-prone AFM.

 

Here's some reading for you. Enjoy! 

 

_________________

 

The electrical power management (EPM) 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 EPM 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 EPM 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 (SOC) of the battery is determined by measuring the open-circuit voltage. The SOC 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 SOC 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 SOC based on adjusted net amp hours, battery capacity, initial SOC, 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 EPM function is designed to perform regulated voltage control (RVC) to improve battery SOC, battery life, and fuel economy. This is accomplished by using knowledge of the battery SOC 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 EPM. The second section describes charging system operation. The third section describes the instrument panel cluster (IPC) operation of the charge indicator, driver information center (DIC) 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 volts.

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 (IPC) for electrical power management (EPM) operation. The BCM determines the output of the generator and sends the information to the ECM for control of the generator field control 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 (SOC). The BCM sends idle boost requests to the ECM.

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)

The ECM directly controls the generator field control circuit input to the generator. The ECM receives control decisions based on messages from the BCM. It monitors the generators generator field duty cycle signal circuit and sends the information to the BCM.

Instrument Panel Cluster (IPC)

The IPC provides a means of customer notification in case of a failure and a voltmeter. There are 2 means of notification, a charge indicator and the driver information center (DIC) SERVICE BATTERY CHARGING SYSTEM message.

 

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. It monitors the generator performance though the generator field duty cycle signal circuit. The signal is 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. 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 a 5 volt 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 volts 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. 

 

• The 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 volts 

 

• Tow/Haul mode is enabled 

 

 

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 volts, depending on the battery state of charge and estimated battery temperature.

Fuel Economy Mode

The BCM will enter Fuel Economy Mode when the ambient air 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 amps and greater than -8 amps, and the battery state of charge (SOC) 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 volts. 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 the headlamps are ON. Voltage will be regulated between 13.9-14.5 volts

Start Up Mode

When the engine is started the BCM sets a targeted generator output voltage of 14.3 volts for 30 seconds.

Voltage Reduction Mode

The BCM will enter Voltage Reduction Mode when the calculated battery temperature is above 0°C (32°F). The calculated battery current is less than 1 amp and greater than -7 amps, and the generator field duty cycle is less than 99 percent. Its targeted generator output voltage is 13 volts. The BCM will exit this mode once the criteria are met for Charge Mode.

Auxiliary Battery Charging (TP2)

The auxiliary battery provision (TP2) can be used to supply electrical power to additional equipment that the customer may choose to add, such as a slide-in camper or trailer, without discharging the vehicles primary battery. The auxiliary battery relay closes when the engine is running, in order to allow the generator to charge the auxiliary battery. The relay opens when the engine is off, so that the accessories will not discharge the vehicles primary battery, which is used for engine starting. If the vehicle is equipped with an auxiliary battery, the relay will be located on the driver's side of the vehicle, next to the underhood electrical center. Generally, a fuse should not be used in the STUD 1 Fuse 68 position of the underhood fuse block, if the vehicle is equipped with an auxiliary battery. A plastic plug may be installed in this position instead of a fuse. If a fuse is installed in this position, the accessories will discharge the primary battery in addition to the auxiliary battery.

 

Instrument Panel Cluster (IPC) Operation

 

Charge Indicator Operation

The instrument panel cluster (IPC) illuminates the charge indicator and displays a warning message in the driver information center (DIC) when the one or more of the following occurs:

 

 

 

• The engine control module (ECM) detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a GMLAN message from the ECM requesting illumination. 

 

• The BCM determines that the system voltage is less than 11 volts or greater than 16 volts. 

 

• The IPC receives a GMLAN message from the body control module (BCM) indicating there is a system voltage range concern. 

 

• 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 Voltage Gauge Operation

The IPC displays the system voltage as received from the BCM over the GMLAN serial data circuit. If there is no communication with the BCM then the gauge will indicate minimum.

This vehicle is equipped with a regulated voltage control (RVC) system. This system turns off the generator when it is not required in order to improve fuel economy. The generator will turn back on when additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems which usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.

SERVICE BATTERY CHARGING SYSTEM

The BCM and the ECM will send a GMLAN message to the DIC for the 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. During cold weather warm-up and high electrical demand, the generator capacity can be briefly exceeded causing this message to be displayed for up to two minutes.

 

[Doug_Scott]

I like this part...  "The generator is a serviceable component. If there is a diagnosed failure of the generator it must be replaced as an assembly. "  It is either serviceable or it is replaceable, they are different terms and meanings.  I was taught that serviceable meant you could actually service it, and replaceable meant you could not service it.  

 

You can monitor the voltage as the PCM reads it by connecting a scan tool to the port under the steering wheel.  I picked up one of those HUD from china, it shows battery voltage(along with lots of other stuff).  My battery voltage will read as high as 15v and the lowest I have seen running was 13.8.  Usually stays in the 14v range.

[Jsdirt]

Yeah, looks like GM's china translation team made yet another mistake. A slight contradiction between those 2 sentences there!   

 

I've been running an Odyssey AGM since '14. I have to charge it at least once a month with my 4-stage charger that has the higher voltage "Odyssey PLT" (PLT = pure lead technology) setting. Since the computer is designed to monitor a regular lead acid battery, it cuts the voltage back prematurely, and never adequately charges this battery.

 

Wish there was a simple way to convert this to an on-demand charging, but have it switch-controlled inside the cab, broken down into 3 settings - Low, Med., and High. That would be fantastic. Would need a frequency generator - I think they make them for computer test equipment, but I don't think they're robust enough to last in a Northeastern USA automotive application. If you cut the wire, it defaults to 13.8v ... which is fine in most cases, but would be overrun whenever I turn on my 60A of dual Viair air compressors.

[STEVEN RAY MARQUEZ SR.]

19 hours ago, Tim Twite said:

I have a 2013 1500 LTZ. It shows around 14 volts on the meter some times less. A few days ago it started running in about the middle of the shaded scale above 14 so my guess 15 to 16 volts all the time.  I replace the battery thinking it was 7 years old and temps were cold might be getting weak.  That made no difference still the same.  When the head lights are on it goes down to just above 14 and as I have read it should be 14.5 when head lights are on.  I do not get any warnings or error messages and everything seems to work fine but am concerned it is over charging.  I took a road trip yesterday and was watching as I drove average speed 75 in a 2 1/2 hour trip a couple of times it went down to just below 14 and stayed there for a few minutes and then climbed right back up and stayed there.  any ideas what is going on or should be checked??

My Suburban does the same thing since new. I've had no problem with it

[Doug_Scott]

On 2/19/2020 at 12:08 AM, Jsdirt said:

Yeah, looks like GM's china translation team made yet another mistake. A slight contradiction between those 2 sentences there!   

 

I've been running an Odyssey AGM since '14. I have to charge it at least once a month with my 4-stage charger that has the higher voltage "Odyssey PLT" (PLT = pure lead technology) setting. Since the computer is designed to monitor a regular lead acid battery, it cuts the voltage back prematurely, and never adequately charges this battery.

 

Wish there was a simple way to convert this to an on-demand charging, but have it switch-controlled inside the cab, broken down into 3 settings - Low, Med., and High. That would be fantastic. Would need a frequency generator - I think they make them for computer test equipment, but I don't think they're robust enough to last in a Northeastern USA automotive application. If you cut the wire, it defaults to 13.8v ... which is fine in most cases, but would be overrun whenever I turn on my 60A of dual Viair air compressors.

Sounds like you have a setup that is simply beyond the capabilities of the stock charging system.  Have you considered trying to replicate the dual battery system that would be installed in the snow plow package?  Or check with an outfitter that does motorhome or that camper shell thing conversion that goes in the bed of a pickup. 

[Jsdirt]

The battery and alternator are more than up to the task. It's that crap computer controlled field winding that won't give it the juice when it needs it. The truck spends alot of time sitting, especially in summer when the wife takes the Marquis - I'll drive the Volvo then. After '95, these damn computers started to drain any battery down (not dead, just lower than I'd like to see) in just 2-4 weeks of sitting ... and then the PCM  will only give the field full power for the first 5 minutes of driving, and then cut the amperage back to nothing! I've had my wipers barely moving across the windshield, because the PCM decided it was time to cut charge current. Ridiculous system. Sucks!!  Pisses me off every single time I drive it. Never had an issue when alternators just charged when they were spinning, and the key was on. 

 

Since it's an AGM battery, the computer thinks it's overcharged or fully charged, but it's far from it. Never had these problems before all this OBD-II computer crap started showing up after 1995. Then things got worse in '07 with computers running EVERYTHING, and staying awake when they shouldn't, and a billion other issues.