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What Makes Today’s Charging Systems “Smart”?

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What makes today’s charging systems “smart”?

Computer-controlled voltage-based charging can be thought of as a semi-smart charging system. But when a charging system can watch the amperage in and out of the battery (amperage-based charging), it is considered a true smart charging system. Today’s smart charging systems are capable of many features and operational modes, including load shedding, start-up mode, battery sulfation mode, deceleration mode, fuel economy mode, windshield de-icing mode, and other features to optimize vehicle charging, emissions, performance, and fuel economy. 

The difference between a regular non-PCM controlled charging system (non-smart system) is that the smart charging system’s primary objective is to supply the electrical needs of all the vehicle’s electrical components and its secondary objective is to recharge the battery.

Smart charging systems can be divided into two charging strategies: voltage-based charging or amperage-based charging. Both charging strategies rely on managing the alternator’s field circuit to control the alternator’s output. The two most common methods to control the alternator field circuit on a smart charging system are decided by where the voltage regulator is located. 

The voltage regulator is mounted internally in the PCM.

The voltage regulator is mounted internally in the alternator and can be remotely controlled using a dedicated hardwired control circuit. 

This last method (No. 2) is the most popular because if the control circuit fails or communications become corrupted to the voltage regulator, the voltage regulator typically will function at a fixed voltage or default mode. This allows the vehicle to still have a semi-functional charging system to limp-in until repairs can be arranged. GM, Ford, Toyota and most other manufacturers are using some form of the smart charging system, but I would like to look at two manufacturers that started out with semi-smart charging systems and have either completely switched to full smart charging or are in the process of doing so.

Honda and Stellantis/FCA (previously Fiat Chrysler Automobiles or FCA) are two popular vehicle manufacturers that both use a smart charging system today, but they use different methods for controlling the alternator to get the results that they want.

Honda smart charging

Honda began using a smart charging system in the early 90s when it switched from voltage-based charging to an amperage-based charging system. Honda’s Dual Mode charging system incorporated an Electronic Load Detection unit or ELD in the under-hood fuse block. The ELD allowed Honda to have two distinct charging modes: alternator low output mode and alternator high output mode. Honda used this system until 2013 when they switched to a single LIN (Local Interconnect Network) BUS that controls the alternator’s output.

The Honda Dual Mode charging system was designed to reduce engine load by 10%, increasing fuel economy and lowering emissions.

During low output mode operation, on a fully charged battery, the Honda Dual Mode system can have a charging setpoint as low as 12.4V. This information is critical to know if diagnosing a charging system issue on an older Honda. We all know that a fully charged battery’s voltage is 12.6V, but early and later versions of Honda’s Dual Mode could only charge the battery to an 80% state-of-charge (12.4V) to achieve the reduced engine load. 

But if you are diagnosing a Dual Mode Honda and are unaware that this is a perfectly normal situation and noticed that the battery voltage was not in the 13.0-13.5 range, you might misdiagnose this as a failed alternator. This is a good example of needing to understand how the charging system is designed to work and not how we as techs expect it to work. The easiest way to ensure that the alternator is not in low output mode is to apply an electrical load by turning on the headlights and the blower motor, which should result in the alternator producing 13.5V or higher.

Honda’s smart charging system evolved in 2013 when they started to use a battery management sensor mounted on the negative battery terminal and a dedicated LIN BUS that connects the alternator, the battery management sensor and the PCM.

Honda uses a master/slave protocol on this LIN BUS: the PCM is the leader, and the alternator and the battery management sensor are followers. In this setup, the alternator receives charging voltage commands from the PCM. The alternator will respond to these commands by adjusting the voltage output and then send feedback to the PCM. When this information is combined with the information that the battery management sensor is supplying, the PCM can operate the vehicle’s electrical system efficiently. Honda’s smart charging system is capable of a charging voltage range of 12.5V to 14.5V in 0.1V increments. Honda even states that in some operating conditions the alternator might bypass PCM control and use a default value.

This system can set several trouble codes and flash warning messages on the driver’s information center e.g., “Check Charging System.” These codes can include LIN communications codes: P16E2 PGM-FI-ACG LIN Communication Error; P0562, if the charging system voltage is too low; P1549, if the charging voltage is too high; or P065A No Charging Malfunction, that could be set by a defective serpentine drive belt or a bad Overrun Alternator Decoupler (OAD) pulley. In this scenario, the pulley spins fine, but the actual rotor in the alternator will not move or will not move fast enough. There have been some issues with failed alternators, broken alternator brackets that cause the alternator to lose its ground and cause excessively high voltages, and some corrosion issues on the battery sensor LIN wire that causes communication issues and check engine lights.

Honda has also had issues with the battery management sensors and has issued recalls on certain 2013-2016 Accords (the battery management sensor was not sealed correctly and could catch on fire).


Smart charging is not new to this manufacturer. In 1985, Chrysler introduced a computer-controlled charging system that removed the firewall-mounted voltage regulator and incorporated it into the power module. This voltage-based charging system incorporated a battery temperature sensor and other sensors to modify the alternator’s charging strategy and engine idling speed. Today’s Stellantis/FCA still control some of their charging systems this way, but slowly, they are moving from voltage-based charging to amperage-based charging on many models and vehicle platforms. 

The most popular 3.6 V6 Dodge Caravan still uses only a voltage-based charging system that is controlled by the Electronic Voltage Regulator (EVR) and its accompanying software located in the circuitry of the PCM. 

The PCM supplies field control voltage using a high side driver to the field control circuit of the alternator via a GEN FIELD CONTROL wire. This circuit is grounded internally in the alternator via the alternator case. The PCM monitors alternator voltage output on the GEN SENSE signal wire from the alternator and compares this voltage to a battery sense voltage output that the Totally Integrated Power Module (TIPM) provides. From these two voltages, the EVR will determine the proper command signal that it will send to the alternator to control the alternator’s target voltage.

If the sensed battery voltage is 0.5 volts or lower than the desired target voltage, the PCM will apply power to the field winding circuit increasing alternator output until the sensed battery voltage is 0.5 volts above the target voltage. The EVR circuit in the PCM will cycle the high side driver providing battery voltage to the alternator field up to 400 times per second (400Hz) on newer models and 100Hz on older models.  It is important to remember that because the voltage regulator is mounted inside the PCM, if the GEN FIELD CONTROL wire is broken or corroded the alternator will not function.

The PCM has the capability to full field (100% duty cycle) the GEN FIELD CONTROL to achieve the target voltage. If the charging rate cannot be properly monitored, because of a broken or corroded GEN SENSE signal wire to the alternator, for example, the EVR will command a limp-in mode and supply a duty cycle of 25% to generate some voltage output.

The GEN FIELD CONTROL duty cycle can be checked using a scanner, a scope or a DVOM. During normal charging operation with minimal loads at idle, the typical GEN FIELD CONTROL duty cycle will be about 35-40% on the scanner or about 4–5 volts using a DVOM. 

Depending on what the PCM is asking for, the duty can be off (0%) and 0V or it can be 100% on (fully fielded) and have 11-12 volts being supplied on the GEN FIELD CONTROL wire.

When Stellantis/FCA started watching amperage and switched to a complete smart charging system they incorporated an Intelligent Battery Sensor (IBS) to measure battery current. The IBS is attached to the negative terminal of the battery and is a small microprocessor. The IBS has a built-in thermistor that calculates battery temperature and other electronics that enable it to calculate the battery’s state of charge, battery internal resistance, charge received, charge delivered and time in service. The IBS is connected to the BCM via a LIN BUS, and the BCM will share IBS information to other modules (PCM) via the CAN BUS. The IBS does not have a direct diagnostic interface and is a slave to the BCM. The IBS is diagnosed through the BCM that will display IBS data, but if there are any trouble codes related to the IBS. they will be stored and read through the PCM.

Dodge, Jeep and Ram have had their share of alternator-related failures, OAD (overrunning alternator decoupler) concerns and many issues with corrosion that have caused charging system failures. There has been a recall of various amperage alternators for 2011 to 2014 Stellantis/FCA vehicles because of an overheating diode failure in the alternator that may result in a possible fire.

Some Jeeps will generate a P057F code (14-volt battery state of charge performance) and display a message “Engine Will Not Operate on Stop/Start Mode” on the driver’s information center, and after the message appears, the vehicle will not enter start-stop mode. The smaller Jeep 3.2L V6 Cherokee is only equipped with one battery under the hood, and it is likely to fail. The fix is a new battery that meets or exceeds the factory battery’s rating, type and size. On the bigger Jeeps such as the Wrangler and Grand Cherokee, if they are setting the P057F code there is a separate supplemental battery located beside the service battery under the passenger seat. This smaller battery is in place to maintain the vehicle’s operation during a start-stop event and has likely failed. 

One special note needs to be made on the Stellantis/FCA smart charging system: The diesel applications are different. The diesel charging systems all have a voltage regulator that is internally mounted in the alternator. The diesel alternator uses a LIN BUS from the PCM to regulate the charging voltage and will use an IBS to monitor amperage.  Unlike the PCM-controlled field windings, the diesel alternator will work at a fixed voltage output if the PCM is unable to communicate with the alternator via the LIN BUS. It will also set codes in the PCM and turn on the check engine light.

Originally, the charging system’s goal was to provide power back to replenish the battery and supply the small amount of needed energy to operate the few electrical devices on the older automobiles such as the ignition system, lights, wipers, blower motor and a radio. 

But as we have electrified so many systems on today’s vehicles, it has resulted in a substantial load on the charging system. By using a smart charging system that will continually supply the ideal voltage and amperage, all the electrical requirements of the modern vehicle can be met while boosting fuel economy, lowering emissions and increasing battery life. 

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