Toyota Sienna Check Charging System / How To Reset?


Most drivers have experienced a loss of power at some point in their lives. It could be your car won’t accelerate or maybe your inside lights dim. You end up taking it to a mechanic and hope for the best. 

The Toyota check charging system is a system that keeps your battery charged while your vehicle is running. Sometimes it will fail and the root cause could be one of several problems. Here is all you need to know about the Toyota Sienna check charging system, what is it, and how to fix it if you have problems. 

First, you must understand what makes up the charging system.

What Is a Charging System?

Makes and models aside, a charging system powers your vehicle while it’s running and keeps up the battery’s charge by sending electrical energy to the battery. The battery stays fully charged because of the voltage regulator. 

The voltage regulator signals the alternator to recharge the battery whenever the battery starts to lose charge. 

Besides keeping the battery charged, there are five basic things the charging system provides electrical current to keep working:

  • The electrical systems of the engine
  • The lights
  • The radio
  • The heater
  • Other electrical accessories

What Makes Up the Charging System?

This largely depends on what year and model car you have as there are some differences in older charging systems versus newer ones. 

Generally, a charging system is made up of three or four main parts:

  • The alternator
  • The battery
  • A voltage regulator
  • Wiring
  • An electronic control unit (ECU) 

The primary difference between the older and newer cars is older models use a voltage regulator while newer cars have an ECU that is built into the vehicle’s computer. The alternator creates the electrical charge to recharge the battery and power accessories. 

How Do I Know When Something Is Wrong?

A charging system failure is something you can’t miss.  First, you may get a warning light on your dash. 

Warning Lights

A check system light means the vehicle is operating completely on battery power without a way for it to recharge like it normally would charge. It will run out quickly and you will be left on the side of a road with a dead battery. 

Other lights that may come on include “battery” or “alternator” dummy lights. This is all a part of the charging system indicating the battery is no longer getting power.

Read: What Does The Service Engine Soon Light In My Car Mean?

Electronics Won’t Work

Beside the dashboard lights, you may see some other common problems associated with a loss of electrical power. Your cabin light may dim or flicker. Your headlights could suddenly dim. Your radio may not work. Your car will suddenly start slowing down. 

Many people don’t realize they have a battery charge issue until they try to start their car. It won’t start. Sure, a jump will get it started but it won’t resolve the problem if you have a battery charging issue because the vehicle is still solely running off the battery without it recharging while running. 

One clear symptom of this problem, according to mechanics, is if the headlights and dash lights are bright after the engine is turned on but dim while it’s idling.

What Causes a Loss of Power?

Several things could be causing a loss of power or a charging system failure in the vehicle. The most obvious problem could be a dead battery. Old batteries lose cells and simply won’t hold a charge. There could be terminal corrosion that prevents the battery from connecting to the wiring properly to get a charge.

Beyond that, problems could be rooted in a bad alternator, a bad voltage regulator, or a problem with the belts. A worn or broken belt can cause a drop in voltage output even if the alternator is good. 

How Do I Determine What the Problem Is?

You can do some basic diagnostics to determine what repairs may be needed before taking it to a mechanic. This can save you a lot of aggravation and money.

The basic rule of diagnosing car problems is to eliminate the simplest problem first.

The first thing to do is to take a serious look at the battery. Take it to a retail store that will recharge it and see if it will recharge. They will let you know if it’s a dead cell and should be replaced. 

Next, check the battery terminal connections. They can be cleaned with baking soda and a wet toothbrush.

A problem with the belt is signaled with dash warning lights coming on, the steering feels heavy, accessories not working, or perhaps the car overheating. You may be able to physically look to see if any belts are slipping, depending on the make and model.

A bad voltage regulator could result in higher voltage being produced and the overvolt can damage the battery. If it improperly limits the voltage, it will keep the battery charged but won’t power everything else as it should. 

An alternator problem will be signaled by the car overall losing power quickly with a decrease in acceleration. 

Once you’ve ruled out the battery, connection, and a belt problem, take the car to a qualified mechanic to look at the voltage regulator or ECU and the alternator. Make sure they look at both and don’t automatically replace the alternator without checking the regulator or the ECU. 

You may be able to check the voltage regulator to see what it’s producing. For a Toyota product, it should be 13.8 volts or less in hot temperatures and up to 15 volts in sub-freezing temperatures, although the exact range for your vehicle will be in your car owner’s manual.

What About the Toyota Sienna Charging System?

One expert Toyota mechanic said that replacing the alternator typically resolves 95 percent of charging system failures. The other issues can be related to the problems mentioned above. 

The first thing to do is see when the warning light comes on and if it goes off. If you see the warning light comes on when you start the car but turns off while the car is running, try running the engine to 2,000 RPMs. A warning light that stays on means you need to check the charging system.

With a Toyota Sienna, you can check the state of your battery with a voltmeter. To do that, turn off all electronic accessories. Disable the fuel pump, connect the voltmeter parallel to battery terminals. Next, crank the engine. 

A voltage that is below 9.6 volts shows the battery needs to be recharged or replaced. 

Next, you can check the drive belt. There are free wear gauges to measure wear. Newer Toyotas may also have a decoupler pully that could be the source of a failure. A pulley that fails means the alternator won’t charge the battery.

A scan tool can help determine if there is trouble with the alternator. A scan tool may be able to show trouble codes. Codes that display low or high voltages indicate a problem with the alternator. 

Toyota also recommending testing the alternator wiring.  Wiggle the voltage regulator connector when you have a scanner attached to see if there are intermittent charges. 

A common problem is sticking or worn carbon brushes that don’t contact correctly with the rotor slip rings, which is why mechanics state it’s best to test the alternator while it’s in the car. You can use alternator testing equipment that measures alternating voltage. 

The final thing to measure is the voltage running between the battery and the alternator. Connect a digital voltmeter between the alternator B+ and the battery B+ terminal. The engine should be running, along with the headlights on and the heater blower fan on “high.”

Then, measure the voltage between the alternator case and battery B- and then between the battery B- and the body. Voltage drops for a Toyota vehicle shouldn’t go higher than .200 volts, according to Toyota.

Toyota vehicles have alternator fuses and it could be a problem with one of the four fuses, not the alternator itself. They should be tested for resistance and each fuse pin should have battery voltage. Checking the fuses is something many mechanics overlook and they just replace the alternator instead. 

It is tricky to check and replace fuses because an amateur can damage the system if they do it wrong. 


Diagnosing the loss of power in your Toyota Sienna isn’t complicated and doesn’t require a lot of tools. Sometimes, a simple solution like getting a new battery will have you back on the road quickly. Understanding what is probably wrong with your vehicle before you take it to a mechanic is a good way to avoid a lot of expensive diagnostics and unnecessary expenses. 

Keeping up with the maintenance on your Toyota Sienna and using a mechanic that knows the Toyota charging system will help keep your vehicle on the road. That includes some routine checks on your charging system and battery, whether you do that yourself or a mechanic.

Leave a Comment