Voltage drop issues plague your car, and they can lead to dire consequences. Voltage drop occurs when there is resistance in an electrical circuit that leads to a reduction (i.e. drop) in voltage between two points in the circuit.
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While it doesn’t sound too bad, it can lead to a dead battery, a car that won’t start, or just a reduction in the number of features that don’t operate on your car.
None of these situations are good, so we’ve gathered the most common car voltage drop issues and their solutions to prevent them from plaguing your car.
#1 – Corroded Or Loose Electrical Connections
Electrical connections are at each end of a circuit, and they can also branch off from that circuit. These connections must provide the ability to transfer power, or the circuit doesn’t function.
How to Fix It
Corrosion and loose connections prevent power transfer in electrical circuits and cause voltage drops.
Corrosion often occurs when dissimilar metals contact each other for an extended period. An example of this is a copper electrical connector fastened to a steel frame rail. The environment can also promote corrosion, such as living near a salty ocean or storing your car in a highly humid area.
You can also have voltage drop when loose connections occur. Fasteners can loosen over time due to vibration and a loose connection will break contact and power transfer.
Fixing these conditions is easy.
Corrosion can be removed using a wire brush or sandpaper and the connection can be secured again. Dielectric grease or a corrosion prevention gel can be applied to the connection to inhibit corrosion from returning, and it won’t affect the voltage.
Loose fasteners can also be resecured, and the fastener threads can have a locking compound applied to prevent the loosening from returning.
#2 – Your Alternator is Faulty
An alternator that is failing will not generate the required power (both voltage and amperage) required to sustain your car while it is running. A bad alternator will make the battery supply the power to your car, which will eventually drain the battery.
How to Fix It
Most newer cars will have an indicator in the gauge cluster that will notify you if the alternator stops generating power. You may see a warning light illuminate or a message indicating a power issue.
Testing an alternator is an easy process using a multimeter. You can measure the power between the battery terminals without the engine running. The battery should read approximately 12.2 to 12.6 volts.
If you start the car, the power between the battery cables should increase to 13.6 to 14.6 volts if the alternator is good. If the voltage doesn’t increase, the alternator is faulty and should be replaced.
Knowing the alternator is good is only half of the validation though. A second check is to ensure the alternator will produce enough power for your car.
You should also turn on the biggest power drawing accessories like the radio, headlights, and air conditioning to ensure the voltage does not drop below 12 volts. If it does, the alternator is undersized and should be replaced with an alternator that has a larger amperage.
#3 – Your Voltage Regulator Is Bad
The voltage regulator in your car prevents the alternator from overcharging or overloading the electrical system and prevents damage. It can also cause the battery to drain when the car is turned off.
How to Fix It
A faulty voltage regulator can be difficult to recognize if your car doesn’t show extreme signs of failure.
Flickering lights and inconsistent idling can be subtle hints that the voltage regulator is going bad.
To test for a faulty voltage regulator, grab a multimeter and test the voltage between the battery terminals.
- If the car engine is running, the voltage displayed on the multimeter should read between 13.6 and 14.6 volts.
- If you turn on all the accessories in the car like the radio, headlights, and air conditioning, the voltage should not drop below 13.6 volts.
- If you step on the gas pedal to rev the engine, the voltage should not go over 14.6 volts.
If either of those situations occur, the voltage regulator is bad.
Voltage regulators used to be separate from the alternator and they could be replaced separately. Current cars use a regulator inside the alternator housing, and you may need to replace the whole alternator unless the regulator can be removed and replaced inside the alternator housing.
#4 – Your Belt Or Tensioner Are Worn
Your accessory belt and tensioner on the engine should last 100,000 miles or more, but until they fail, they can cause a voltage drop.
How to Fix It
The accessory belt on your engine touches all the pulleys to drive the air conditioning, alternator, and water pump. Over time the belt will wear on the surface and can eventually slip.
Slippage causes a voltage drop as the alternator can stop producing power for a brief time. Checking the belt for excessive wear and cracks can determine if it is ready to be changed or it can last a few more miles. If you find cracks or missing pieces of the belt, change it before it completely fails.
The tensioner should keep the accessory belt tight, but if it sticks it can allow the belt to slip. Most newer cars have an automatic tensioner to provide the right amount of tension on the belt.
If the belt is making a squealing noise, the power steering stops working consistently, or your car is overheating, the tensioner may have gone bad.
Check if the belt can move up and down more than ½-inch with a slight amount of pressure. If it can, the tensioner isn’t doing its job and needs to be replaced.
#5 – Your Car Battery Is Old And Failing
Older car batteries lose their ability to hold a charge in extreme heat and cold. If you find that you don’t have enough power to start your car or the voltage fluctuates with the changing weather, an older battery could be the issue.
How to Fix It
Car batteries are ideally replaced every three to five years to keep from experiencing voltage drops, but really most of us don’t decide to replace a battery until it’s failing.
Batteries have a date sticker that should be marked when the battery was manufactured or when the battery was purchased and the warranty period started.
Older batteries can show signs of corrosion on the terminals, a bulging case, and they can start to leak battery acid. You may detect a rotten egg smell near a leaking battery too.
If the battery is draining overnight, causing electronic malfunctions, and showing signs of old age, it’s best to replace the battery before it completely fails.
#6 – Electrical Components Are Overloading The System
Your electrical system is designed to power certain accessories, but many of us are guilty of adding more equipment than the system can handle.
Adding high-demand electronics can strain and overload the electrical system to cause voltage drops.
How to Fix It
Fixing an electrical overload can be completed by limiting the demand on the system at one time or adding extra load capacity to the system.
Limiting the demand may mean you can only run certain accessories together such as the large stereo system and the headlights. It may take a few tries to determine the demand strategy that will prevent voltage drops, but it is one way to manage the problem without changing how you use your car.
A second way to counteract the voltage drops is to add extra capacity to the electrical system. That could be accomplished by adding a higher output alternator to keep up with the demand.
If the stereo system is the major problem, you can also add a capacitor to store power for the audio system rather than pull from the main electrical system. Just don’t add too much power to the system that it overloads the circuits, burns the wiring, and blows fuses.
#7 – Shorts Circuits And Faulty Wiring Are Causing Problems
The last major reason voltage drops occur is faulty wiring and short circuits disrupting the voltage. Shorts circuits tend to happen because exposed wiring contacts a grounded surface. As wiring ages, it can develop corrosion and disrupt voltage.
How to Fix It
Short circuits may be hard to find, but they are thankfully easy to fix. Any exposed wiring can be repaired with non-conductive electrical tape or shrink wrap and then additionally covered with corrugated plastic material to prevent additional damage.
Wiring ages and loses conductivity, and after 20 years may require replacement to restore conductivity. There is a reason that older car restorations replace wiring harnesses with new updated circuits.
New wiring contains better materials that will restore voltage drops and add extra power transferring capacity so you can add new electronic accessories.
