Auto Anatomy: Car Relay

All about car relays

  • What is a Car Relay?
  • Working of a Car Relay
  • Function of a Car Relay
  • Types of Car Relays
  • Problems With Car Relays
  • FAQs

Car relays are pivotal in vehicle electrical systems, serving as key components for controlling various functions. They are centred on an electromagnetic coil, for efficient management and directing of electrical currents. Despite the discreet nature of a car relay, it is instrumental in automating essential functions like the starter motor, headlight and fuel pump.

Let’s uncover everything you need to know about car relays. 

What is a Car Relay?

A car relay functions as an electrical switch, employing an electromagnetic coil to regulate the opening and closing of one or more contact sets. It is an important car engine’s part which acts like a remote control switch to enable a small current to command a larger one. In a vehicle, relays are crucial components that help manage and control various electrical systems, ensuring efficient and safe operation.

Working principle of car relay
Car relays act as electrical switches to control high-current circuits through a low-current signal

How Do Car Relays Work?

Car relays utilise electromagnetic induction with a central coil. When an electrical current energises the coil, it creates a magnetic field. The relay contacts are open in the default state, maintaining an open circuit. Applying a small current to the coil induces a magnetic field that attracts a movable core, closing the contacts. 

This completion of the circuit allows a larger current to power components like the starter motor or lights. When the coil current is interrupted, the magnetic field collapses and the relay contacts return to their open position, breaking the circuit. Car relays are crucial in efficiently managing electrical currents in a vehicle’s systems.

Function of Car Relays

A car relay functions as an electrical switch that controls high-current circuits with the help of a low-current signal. They are vital for automating and controlling various electrical components in a vehicle. Some common car relay functions include controlling the starter motor, powering car headlights, managing fuel pumps and operating cooling fans.

Function of car relays
Controlling starter motor and headlights are some of the functions of car relays

Types of Car Relays

There are several types of relays used in cars, each designed for specific applications:

Electromagnetic Relays

As the most common relays in vehicles, electromagnetic relays utilise an electromagnetic coil to control a switch. The function and working principle of electromagnetic relays has been discussed above. 

Solid-State Relays

In contrast to electromagnetic relays, solid-state relays use semiconductor devices for switching. This results in faster response times and increased durability. 

Solid-state relays are known for their efficiency and reliability, making them suitable for applications where rapid and frequent switching is required. Their design lacks moving parts, reducing wear and tear compared to electromagnetic relays.

Types of car relays
Electromagnetic relays are the most common type of car relays

Time Delay Relays

Time delay relays are designed to introduce a delay in the circuit’s operation. This feature is handy in applications like intermittent wipers, where a controlled delay is needed before activating or deactivating a specific function. 

These relays enhance the precision and timing of certain electrical operations in vehicles.

Protective Relays

Protective relays are specifically engineered to safeguard circuits from overloads or faults. By quickly detecting abnormal conditions, such as excessive current or voltage, protective relays can isolate the affected circuit, preventing damage to sensitive components. 

These relays are important to maintain the integrity of a vehicle’s electrical system, contributing to safety and preventing costly repairs.

Common Problems With Car Relays 

Despite their importance, car relays can experience issues. Addressing these issues requires careful troubleshooting and sometimes replacement. Here are some common problems with car relays and their possible solutions.

Sticking Relay

Car relays may stick in either the open or closed position, disrupting normal operation. This issue can arise from prolonged use, dirt accumulation or wear and tear.

How to Fix It

Replacing a car relay is the only solution if it is found to be sticking or beyond repair. Following a car maintenance schedule and periodic checks can help prevent sticking relays.


Excessive heat is a common culprit for relay failure, often stemming from poor electrical connections or overloading. High temperatures are likely to compromise the integrity of the relay’s internal components. Moreover, car relay issues can also result in overheating of the car engine which might require professional intervention if not dealt with timely.

How to Fix It

To address overheating issues, ensuring proper electrical connections and avoiding overloading the circuit is essential. Additionally, installing heat shields or relocating the relay to a cooler area within the vehicle can mitigate overheating concerns.

Coil Failure

The electromagnetic coil is a critical component of a relay and its failure can render the entire relay useless. Coil failure may result from manufacturing defects, electrical surges or prolonged usage.

How to Fix It

Identifying coil failure can be done through testing with a multimeter. Checking for continuity and resistance in the coil can pinpoint faults. If the coil is faulty, replacing the relay with a new one is the recommended solution.


Moisture and corrosion can affect relay contacts, leading to poor conductivity and potential circuit interruptions. This issue is particularly common in vehicles exposed to harsh environmental conditions.

How to Fix It

The car relay fixes against corrosion issues include cleaning the contacts with an electrical cleaner. This not only removes the corrosion but also helps restore proper conductivity. Moreover, after the car rust removal process, you can apply a protective coating to prevent future corrosion.


Can I replace my car’s relay myself?

Yes. Many relays are accessible and can be replaced by following the vehicle’s service manual.

How do I test a relay?

Use a multimeter to check for continuity, resistance and proper operation of the relay coil. However, if you are not confident about testing the relay, you may opt for dubizzle’s car inspection services for a thorough inspection to make informed decisions.

Are all relays interchangeable?

No. Relays come in various types and configurations, so it’s crucial to replace a faulty relay with the correct one.

Can a relay fail intermittently?

Yes. Relay contacts can develop intermittent faults, causing sporadic electrical issues.

There we have it – a detailed overview of car relays. These units discreetly control essential electrical functions in a car. Understanding their functions, types, problems and fixes, empowers car owners to address issues promptly. Moreover, regular car maintenance and proper handling of electrical components can contribute to a reliable and efficient vehicle.

That said, if you are searching for a reliable vehicle, here are some used cars for sale in the UAE where you might find your ideal ride.

For more information on car parts and accessories, stay connected with the dubizzle car blog.