What is Car Earthing? Mechanisms, Effects, Benefits, and Precautions for Modern Cars

"Earthing a car makes the engine feel lighter."

"Older cars run better with additional earth cables."

"What exactly is earthing in a car?"

When researching car customization or electrical components, you might come across the term "earthing."

Earthing generally refers to optimizing the negative electrical path in a vehicle's electrical circuit or adding supplementary earth cables.

However, it's crucial to understand that:

It's not simply a matter of earthing guaranteeing an increase in horsepower,

improved fuel efficiency, or

enhanced throttle response.

Cars are designed by manufacturers with all necessary earth circuits already in place.

On the other hand, if the flow of electricity is impeded by factors such as:

corrosion of terminals,

loose bolts,

degradation of earth cables, or

increased resistance at contact points,

it can lead to voltage drops or malfunctions in electrical components.

This article will provide a clear explanation of:

What car earthing is,

The concept behind earthing,

When it is effective, and

Precautions to take with modern cars.

What is "Earth" in a Car to Begin With?

In household electrical systems, "earth" can refer to grounding, which means releasing electricity into the ground.

However, "body earth" used in automobiles has a slightly different meaning.

In a typical 12V car:

Electricity flows from the positive terminal of the battery to electrical components, and then

returns to the battery via the negative path.

If a dedicated negative wire were to be run from every electrical component back to the battery, the amount and weight of wiring would increase significantly.

Therefore, most cars utilize the metal chassis as a common electrical path.

This is what is known as

"body earth."

So, the car's earth is not about

discarding electricity into the ground;

instead, it uses the chassis as part of the circuit that

returns electricity to the battery.

Even in Nissan's owner's manual, when connecting booster cables, it instructs to connect the negative side to the vehicle's body earth, indicating that the chassis is used as an electrical return path.

Why is the Car Body Used for Electrical Circuits?

The car body has a large metal structure.

Utilizing this as a common negative path offers several advantages:

Reduces wiring.

Keeps vehicle weight down.

Decreases the number of parts.

Allows for efficient placement of electrical components.

For instance,

headlights,

ECUs,

starter motors,

alternators,

various sensors,

audio systems, and

electric fans

are among the many electrical components that utilize earth points on the chassis or engine.

However, not everything is simply connected to the same metal plate.

In modern cars, electronic control is complex, and earth circuits are meticulously designed according to the purpose of each device.

Why Does the Engine Also Need an Earth Cable?

Although the engine and transmission are made of metal, there are elements such as:

engine mounts,

rubber bushings,

paint, and

joints.

Therefore,

it's not always true that "the engine is made of metal, so it's naturally in perfect electrical continuity with the chassis."

For this reason, elements such as:

earth straps and

earth cables

are installed between the engine and the chassis.

The starter motor, in particular, requires a large current during engine start-up.

Therefore, it's crucial that the electricity flowing from the battery to the starter can return to the battery through a path with sufficient thickness and low resistance.

What Happens if the Earth Condition is Poor?

Earth paths require the lowest possible electrical resistance.

However, over long periods of use, resistance can increase due to factors such as:

corrosion of terminals,

loose bolts,

moisture,

dirt,

cable degradation, or

poor contact between terminals and metal surfaces.

If a large current flows through an increased resistance, a

voltage drop

occurs.

DENSO TEN's technical documentation also explains that if resistance exists in the earth wiring of electrical components, a voltage drop will occur when a large current flows, which can affect the sensor's ground level and lead to device malfunction.

This means that earthing is not about just

"any connection will do."

It is crucial to maintain sufficiently low resistance even when the required current flows.

Potential Symptoms of Poor Earthing

If there is a clear malfunction in the earth path, various symptoms may arise.

For example, these could include:

weak starter rotation,

difficulty starting the engine,

unstable lights,

unstable operation of electrical components,

impact on sensor signals, or

unstable charging system status.

However,

poor throttle response,

poor fuel efficiency, or

engine not revving properly

cannot be solely attributed to

"earthing issues."

Even with the same symptoms, many other causes could be at play, such as:

battery,

alternator,

ignition system,

fuel system,

sensors,

wiring, or

poor contact.

What is Earthing?

In the context of car customization, "earthing" generally refers to the method of

adding thicker cables separate from the existing earth path to electrically connect the engine, body, and areas around the battery.

For example, additional cables are installed from:

the engine to the body,

the transmission to the body, or

specific electrical component areas to earth points.

The underlying concept is to

add an electrical path with lower resistance in parallel with the existing path.

Does Earthing Really Work?

This is the most crucial part.

The answer is:

"It depends on the vehicle's condition."

For cars where the original earth cables and contacts are in good condition and sufficiently low resistance is maintained as designed by the manufacturer, adding more earth cables may not result in significant changes.

On the other hand, for vehicles that are:

older,

have advanced corrosion,

have poor contact at the earth terminals, or

have degraded earth cables,

repairing or improving the electrical path can bring them closer to their original state.

The important thing is to think of it not as

"enhancing performance with earthing,"

but rather as

"restoring a deteriorated electrical path to its normal state."

Reasons Why Older Cars Are Said to Feel More Effect from Earthing

In older vehicles, factors such as:

oxidation of terminals,

corrosion of metal surfaces,

degradation inside cables, or

changes in the condition of mounting bolts

can occur.

Honda's maintenance documentation also advises cleaning battery terminals if they are dirty or corroded, and ensuring they are securely tightened.

If these basic contact conditions deteriorate, electrical resistance can increase.

Therefore, it's conceivable that older cars, after having their earthing system maintained, might experience improvements such as:

a change in starter rotation,

more stable lights, or

improved operation of electrical components.

However, even in this case,

it's not necessarily the additional cable itself that produced the performance.

It's likely due to the normalization of a degraded earth path.

Does Earthing Increase Horsepower?

Simply adding earth cables to a normally functioning vehicle does not guarantee

an increase in the engine's maximum power output.

Engine output is determined by many factors, including:

intake air,

fuel,

ignition,

combustion,

supercharging,

engine speed,

mechanical losses, and

control systems.

If there was an abnormality in the earth path, and

sensors or the ignition system were not functioning correctly,

then correcting this could potentially restore the engine to its original state.

However, it is not appropriate to consider earthing as a simple performance-enhancing device, as if

adding an earth cable to a normal 100-horsepower engine will turn it into a 105-horsepower engine.

Can Throttle Response Change?

In a car where electrical contact conditions have deteriorated, and then repaired, if the

electrical system,

sensors,

ignition system, and

electronic throttle

return to a normal electrical environment, the driver may perceive a difference in response.

However,

earthing does not uniformly guarantee improved throttle response.

Throttle response is also influenced by factors such as:

electronic throttle control,

torque characteristics,

transmission,

turbocharger,

vehicle weight, and

drivetrain.

As explained in the previous article "What is Throttle Response?", it's not determined by a single factor.

Does Fuel Efficiency Improve?

The same applies to fuel efficiency.

If a clear problem in vehicle control is caused by poor earthing, and this is normalized, it's possible that fuel efficiency could improve as a result.

However,

it cannot be said that adding earth cables will always improve fuel efficiency.

Fuel efficiency is influenced by many conditions, such as:

driving style,

tire pressure,

ambient temperature,

engine oil,

combustion state,

traffic conditions,

air conditioning, and

vehicle weight.

It is more appropriate not to simply quantify the effects of earthing alone.

Is "Thicker Earth Wires are Better" Correct?

Cables have electrical resistance.

Generally, resistance is reduced when a cable is:

thicker,

shorter, and

made of highly conductive material.

However, it's not simply a matter of

just installing the thickest cable possible.

What's important is the entire system, including:

required current capacity,

cable length,

terminals,

contact surfaces,

fixing method,

routing,

heat, and

vibration.

Even with a very thick cable, if the

contact surface between the terminal and the body is corroded,

the bolt is loose, or

it's connected over a painted surface,

you won't achieve sufficient effect.

Sometimes "Contact Points" are More Important Than Cables

When considering earth paths,

the connection points

are crucial, not just

the cables themselves.

For example, these include:

battery terminals,

crimp terminals,

bolts,

contact surfaces with the body, and

contact surfaces with the engine.

Even if the cable has low resistance, if there is high contact resistance at the connection points, a voltage drop will occur there.

Therefore, for older cars, before adding supplementary earth wires, it's important to

check the condition of the genuine earth points.

Simply Checking for Continuity with a Tester is Insufficient

When inspecting earthing, one might assume

"it has continuity with a tester, so there's no problem."

However, this alone may not be sufficient.

Even if there's continuity when almost no current is flowing, the effect of resistance can become apparent when large currents flow, such as with the:

starter,

headlights, or

electric fan.

Therefore, in automobile maintenance, the method of

measuring voltage drop under actual load

is used.

To assess the quality of an earth path, it's not just about whether it's

"connected,"

but about

"how much voltage is lost when the necessary current flows."

Be Cautious with Additional Earthing in Modern Cars

Compared to older cars, the electrical systems in modern cars are very complex.

For example, they incorporate:

charging control,

idle stop systems,

battery status monitoring,

current sensors,

power management by the ECU, and

hybrid systems.

Therefore, it cannot be simply assumed that

"it's fine to connect directly to the negative terminal of the battery."

In fact, Nissan explicitly states for some models not to directly connect electrical components or earth wires to the 12V battery terminal, warning that improper wiring can lead to malfunctions or a dead battery.

Therefore, when adding earth wires or electrical components to a modern car, it is essential to check the:

vehicle manufacturer's owner's manual,

service manual, and

product manufacturer's specifications.

Why are Battery Current Sensors a Problem?

Some modern cars are equipped with current sensors, typically on the negative side, to monitor the battery's charge and discharge status.

The vehicle uses this information to determine:

charge level,

alternator control,

idle stop function, and

power management.

If a path is created that differs from the manufacturer's design, some of the current may bypass the sensor.

This can lead to a discrepancy between the

actual current flowing

and the

current recognized by the vehicle.

While not all cars have the same structure, this is one reason why it's advisable to avoid self-made earthing in modern cars.

Special Caution for Hybrid and EV Vehicles

Hybrid vehicles and EVs also have 12V systems.

However, they also feature high-voltage systems that differ from conventional 12V cars, such as:

high-voltage batteries,

inverters,

high-voltage motors, and

DC-DC converters.

It is extremely dangerous for general users to touch high-voltage cables, such as those that are orange.

Do not attempt to add wiring to the high-voltage system on your own judgment with the intention of "strengthening the earth."

For hybrid and EV vehicles, it is safer to consult a qualified service provider with specialized knowledge for any electrical work beyond manufacturer specifications.

Is "Static Electricity" discussed earlier the same as earthing?

Let's clarify this as well.

In the previous article, we discussed:

static electricity generated in cars,

human body electrification,

resin component electrification, and

tires and road surfaces.

On the other hand, this article's discussion of earthing primarily concerns the

return path of current in a vehicle's 12V electrical circuit.

In other words,

static electricity countermeasures

and

body earthing for electrical systems

are not the same thing.

While the word "earth" is common to both and can lead to confusion, it's important to consider their electrical purposes and phenomena separately.

Things to Check Before Earthing

Before considering earthing, it is recommended to first check the original condition.

You should check:

if there is any corrosion on the battery terminals,

if the terminals are loose,

if the genuine earth cable is damaged,

if there is any abnormality in the earth strap between the engine and the body,

if there is any rust or corrosion at the earth points,

if the battery itself has deteriorated, and

if there is any problem with the alternator's charging status.

Before adding earth wires, it is essential to first confirm

whether the original electrical circuit is in good condition.

When Repairing Genuine Earth Should Take Priority Over Adding Earth

For example, if the genuine earth cable is corroded, it's more fundamental to

properly repair the degraded genuine cable or terminals

rather than just

adding an extra cable as is.

Prioritizing the restoration of the manufacturer-designed electrical path to its normal state is crucial.

Especially if:

the starter suddenly became weak,

warning lights are on,

electrical components are unstable, or

the battery repeatedly dies,

prioritize fault diagnosis over customization.

Precautions When Performing DIY Work

The area around the battery is where large currents can be supplied.

If you short the positive terminal with the car body using tools, there is a risk of large sparks and excessive heat.

Since flammable gases may be generated from the battery, caution is required regarding sparks and open flames.

Honda also advises, for battery terminal maintenance, to disconnect the negative terminal first when removing and connect the positive terminal first when installing to prevent sparks from short circuits.

However, depending on the car model, removing the battery may require resetting:

the clock,

power windows,

learned values,

security systems, and

electronic controls.

Always check your vehicle's owner's manual.

Next Science's View on "Earth" and Electronic Environment

Next Science positions the

electronic environment

as one of its technological domains.

Vehicles and machinery operate within various electronic elements such as:

voltage,

current,

contact resistance,

electrification,

materials, and

potential difference.

On Next Science's Technology page, the electronic environment is treated as a research area alongside friction/lubrication, combustion/fuel, and others.

Furthermore, the ORBITRON series includes products like "Smart Earth Monoblock C3" and "Smart Earth Monoblock C4," which focus on the electronic environment of vehicles and machinery.

However, general additional earth cables and products developed by Next Science from the perspective of the electronic environment should not be simply treated as the same.

It is important to differentiate between:

what the product's purpose is,

how it works,

where it is installed, and

what the vehicle's electrical system is like.

5 Key Points When Considering Earthing

When considering car earthing, it becomes clearer if you think in the following order:

First, is the genuine earthing normal?

Next, are there any corrosion on the contact points or terminals?

Then, are there any problems with voltage drop under load?

Does the car have a battery current sensor or charge control?

Will additional wiring affect the manufacturer's power management?

Especially with modern cars, caution is required regarding the idea that

"because an installation method was effective in old cars, it will be the same for current cars."

Conclusion: Earthing Starts with Understanding the "Return Path of Electricity"

The most important thing to understand about car earthing is that

the chassis is used as the negative path of the 12V electrical circuit.

Electricity used by the engine and electrical components returns to the battery via the body and earth cables.

If there is any

corrosion,

looseness,

degradation, or

poor contact

in this path, resistance will increase, potentially leading to voltage drops and electrical system malfunctions.

Therefore, it is meaningful to optimize the earthing condition.

On the other hand,

it is not guaranteed that adding an earth cable to a normal car will necessarily increase horsepower,

improve fuel efficiency, or

enhance response.

The first priority should be to

maintain the genuine earth circuit in a normal state.

And with modern cars, due to the presence of

charging control,

battery current sensors,

various ECUs, and

hybrid/EV systems,

additional wiring requires more caution than ever before.

Earthing is not simply about

adding more thick cables.

Understanding where electricity flows from,

where it passes through, and

how it returns to the battery—that "return path of electricity"—is the first step towards proper earthing.