With raw power under your hood from the battery and engine, no smaller electrical systems or wiring can provide the uncontrolled current. This is where the voltage regulator comes into play, essentially acting as a “surge protector,” controlling the amount of available power to the various systems under your hood.
Unfortunately, voltage regulators can (and do) fail from time to time. Here are the most common symptoms of a faulty voltage regulator and the replacement cost.
How Does an Alternator Voltage Regulator Work?
There are many alternative regulators on the market, but all serve the same purpose. The purpose is to convert direct current to a fixed current that won’t damage the other systems in the vehicle.
Let’s take a look at some of the components that make up the circuit to better understand the regulation function.
Battery
The battery is a reservoir to store energy, it is on standby to start the car and supply energy if the power supply is depleted.
But if you relied solely on the battery power, your car wouldn’t run for very long, you would also need to charge the battery.
Alternator
That’s why we have the alternator. The alternator is the component that produces that power. As you drive down the road, the alternator produces energy to run the system, and then the excess energy is used to recharge the battery.
Voltage Regulator
The voltage regulator will maintain a maximum amount of voltage in the circuit, therefore it can prod the alternator to increase production or tell it to reduce energy production.
The goal is to create a stream of current that can run the vehicle in a consistent manner. And the extra power doesn’t go to waste, it charges the battery.
Where Is the Voltage Regulator Located?
For most modern vehicles, the voltage regulator is included in the alternator assembly. This is an improvement in terms of reliability and simplifies the charging system.
However, if you have an older vehicle, especially something from the 1990s or earlier in which case the vehicle may have an external voltage regulator.
The external voltage regulators were typically located on the fender well or the firewall. External voltage regulators were quite popular on Ford, GM, and Chrysler products of that era.
Common Symptoms of a Bad Voltage Regulator
The good thing about voltage regulators is that technical problems usually develop over an extended period of time, giving you ample time to identify the problem and (hopefully) fix the problem before it fails completely.
In order to properly diagnose a problem, first you must identify the warning flags and then use a multimeter or other basic diagnostic tool to confirm the problem.
There are common symptoms, based on your vehicle type, you should look for one or both:
#1. Flickering/Dimming Lights.
You are most likely to observe this with your headlights, but it may also occur with your other vehicle lights, interior lights, dash lights, and even your stereo display.
When the voltage regulator is not controlling current flow properly, the lights may randomly brighten and dim, or flicker while driving. You will notice this especially when you are at idle ( when using the headlights, wipers, etc) versus driving 70kmh on the highway.
This could indicate battery or alternator problems as well, but the pattern is basically the same with a bad voltage regulator; the lights get bright (meaning you’re overcharging) and then dim (undercharging).
As a rule, the acceptable voltage readings should be, while running, 13.5-14.7V (if your readings are consistently outside those limits, you probably have an issue with your regulator). You want to fix this soon because voltage surges and out-of-spec charging can permanently damage LED lights and other components.
#2. Dead Battery.
Although your battery is a dead battery due to many issues, such as leaving the lights on, alternator malfunctioning, and a bad regulator, it can severely hurt the life of a modern battery.
Most modern cars run on Absorbed Glass Mat (AGM) and enhanced flooded batteries instead of the lead-acid battery that vehicle manufacturers commonly used in the past. These battery types are certainly more efficient, capable of charging/discharging at a much quicker rate, but they are also much more sensitive to charging voltages.
When your voltage regulator is dead, it can over charge (typically more than 14.7V) damaging the battery internally, decreasing it’s lifespan (obviously not good) or worse yet undercharging (under 13.5V) resulting in deterioration across the plate(s) due to a phenomenon called sulphation where the battery capacity becomes lost.
Most modern vehicle computers don’t allow too much voltage variation and will typically automatically enter a “safe mode” and limit the range of vehicle functionality.
If your car battery is relatively new and keeps dying, or you are having problems with the battery holding a charge, and these problems/issues are compounded by other electrical issues, you might have a regulation problem.
Again, take special notice of this symptom in junction with start-stop vehicles or modern vehicles with overly complex electrical systems.
#3. Check Engine or Battery Light On.
There can be many causes, but it won’t hurt to get a scan for any diagnostic trouble codes (check engine light) or do a quick voltage measurement (battery light on) with a multimeter to see if this is the problem.
It is possible that a check engine light might indicate a charging system problem; if you have a battery light on, though, then you are having a charging fault.
The majority of vehicles on the road today have ECMs (engine control module/s) which monitor charge system voltage. When your voltage is not within the acceptable range (commonly 13.5-14.7 volts), the warning lights on your dashboard will activate.
The battery light specifically refers to a charging fault, whereas the check engine light can store DTC(s) (diagnostic trouble codes) if it was something such as P0562 (System Low Voltage). Any basic code reader should enable you to read any voltage fault codes.
With the onset of modern vehicles, before DTC codes were implemented, the battery light was still a good indication of a charging fault, including a voltage regulator fault.
#4. Electrical Accessories Not Working.
Today’s automobiles rely heavily on stable voltage for operation. If the voltage regulator fails, you may find that your power windows open more slowly, the automatic door locks operate erratically, or your radio/infotainment system occasionally resets itself.
High beam headlights, depending on the draw, may function intermittently or not at all.
Steering assist may feel inconsistent on electric power steering. A dash camera or radar detector may reset while driving, and USB charging ports may charge and shut off intermittently.
These symptoms progress slowly and are usually most relevant when the vehicle is parked or when you utilize multiple accessories at once.
Older vehicles may have fewer electronic symptoms since there are fewer electronic systems, although basic power accessories would also be affected.
#5. Fluctuating battery/voltage readings.
If you are checking your voltage with a multimeter, a failing regulator can do many odd things with the readings. A proper charging system will consistently show voltage around 12.6V when the engine is off, and 13.5- 14.7V when running.
With a bad regulator, you will see wildly fluctuating numbers, even when you are not changing the engine speed or electrical load.
If your vehicle has a digital voltage display, which is common in most cars since the middle of the 2000s, you will notice the voltage reading bouncing between numbers while driving.
Furthermore, this can happen in both old and new vehicles, but new ones may produce trouble codes when the voltage does not appear regular.
Your local auto parts store often does a free battery/voltage test if you do not have access to a multimeter.
#6. High Voltage Output.
If you are measuring the voltage at the battery when the engine is running, and see readings above 14.7V, this is a strong indicator that the voltage regulator is malfunctioning.
This condition is referred to as overcharging, which can wreak havoc on a modern automobile, especially since many modern vehicles have sensitive electronics and AGM battery technology.
As stated previously, a car’s charging system should maintain approximately 13.5-14.7V, depending on manufacturer specifications, so a “bad” regulator allowing the voltage to climb above 16V qualifies as excessive.
This condition can cause higher than desired voltage readings, which can damage expensive electronic control modules, pose a risk that LED and traditional bulbs may prematurely fail, and create battery life concerns.
In late model vehicles, the computer may be programmed to detect overcharging and activate warning lights or take the system to a protective mode. Regular voltage readings performed during routine maintenance can help you identify excessive voltage conditions before they become a huge expense.
#7. Intermittent Power Drops.
Although a defective regulator can result in problems with many components, like the fuel pump or ignition system, or anything else that needs a minimum amount of voltage.
You may experience rough idle, sporadic acceleration, or engine sputtering when you need it. While it may not seem like a big issue, it’s important because it’s an indication of power not getting regulated properly.
When a voltage regulator is read to fail, there can be significant power swings, which might affect vehicle performance.
You may feel or see in the gauges a loss of power, experiencing a lag or roughness on idle, and even sluggish acceleration, particularly when heavy electrical loads are present (like running the AC and headlights).
Hence, modern fuel pumps, ignition systems, and fuel injectors only work correctly on stable voltage, which is extremely important since unstable voltage, in vehicles with electronic throttle control (that is, most vehicles on the roads), can impact throttle response.
Older vehicles may tolerate limited amounts of loss of stable voltage but may show similar symptoms, especially with acceleration and other electrical demands are being drawn.
#8. Instrument Cluster Problems.
Like all electrical items, they need a stable voltage supply to provide you with the relevant information to drive the vehicle.
With a defective regulator, erratic behavior of gauges can occur (for example, sweeping up and down, incorrect readings, and intermittent failures). Digital displays may only dim, flicker, or produce random segments.
In newer vehicles (last 15 years), the whole cluster at times may reset drives or have blatantly incorrect readings. Although there are modern vehicles with mostly analog gauges, the same power fluctuation issues may present themselves with erratic gauge needle movements, and total failure would be rare.
This symptom is worrisome since it can potentially prevent you from monitoring important information like your vehicle’s speed, engine temperature, and fuel level.
While the instrument cluster may operate correctly when you start the engine, it may start to misbehave when the charging system is online.
#9. Battery Terminal Corrosion.
While battery corrosion can happen for many reasons (like acid leaks, etc), when there is rapid and/or odd corrosion development and/or appearance, it is typically an indication of a voltage regulator issue.
When a regulator is allowing a battery to overcharge, the battery may heat up and vent gases, which can accelerate battery terminal corrosion (which is usually a blue-green or white crusty buildup).
In modern vehicles with AGM batteries, unusual corrosion should be noticed, as AGM batteries will often produce hardly any corrosion in normal charging environments.
Cost of Replacing a Voltage Regulator
In most modern cars (especially within the last 15-20 years), a voltage regulator is included with the alternator assembly.
This means in most of these applications, you will need to replace the entire alternator unit, instead of just the regulator.
A new alternator can cost anywhere from $200-$600 in parts, depending on your car’s make and model, as well as whether you are using OEM or aftermarket parts.
Some luxury cars may cost more than this. Labor will range from $200-$400, as this job typically takes 2-3 hours, depending on the engine layout and accessibility.
That means the entire replacement cost for your regulator and alternator is probably going to be somewhere between $400-$1,000.
While this sounds cumbersome compared to paying for just a new voltage regulator, you can end up saving money by having all new parts and, in the long run, having a more dependable alternator (less likely to break).
- With any luck, you’ve paid for labor costs once.
- You will have all new alternator parts.
- Newer alternatives tend to be more reliable than a regulator.
- Many remanufactured alternators have a warranty.
If you’re driving an older car (pre-2000) and the car has an external voltage regulator, you might be able to replace just the regulator. Parts would be anywhere from about $40-$140 for the regulator, and you would pay about $140-$240 for labor.
In any case, if you really do have over 100,000 miles and it’s still the original alternator, consider having it replaced even if it’s just the regulator that has failed, you will not have to pay to have the labor done twice in a short amount of time because the alternator is at end of normal service life.
Can I Drive with a Failing Regulator?
No, you should not drive around with a faulty voltage regulator. Most modern vehicles consist of heavy electronics and are highly susceptible to damage from an electrical system failure, especially the battery charging system.
If the voltage regulator is not functioning properly, there are potential hazards of driving with a faulty regulator.
- You could damage your vehicle’s computer (ECM/PCM) or other costly electronic components.
- You could have a premature battery failure.
- You could stall, lose power steering, or be left stranded.
- You could also burn out costly LED-type lighting systems.
It is usually best to have your vehicle towed to a repair shop or get a mobile mechanic to come to your location. If your choice is to drive with the faulty voltage regulator, then limit the use of electrical accessories and have it repaired as soon as you have the opportunity.