ignition relay

Main Relay Symptoms, Function & Replacement Cost

In Electric by Magnus Sellén3 Comments

ignition relay

The main relay of an automobile is undoubtedly one of the most important and essential components of a car.

It controls the computers and the entire fuel system of your car.

The moment you turn the key before you even start the engine, this relay will be activated and without this relay your car’s computer will not get power, your car’s fuel system will not be turned on and as a result your car will not start.

So it is safe to say that your car will not go anywhere without the main relay. The main relay is designed to last a lifetime, but since it is an electromagnetic component, it may eventually fail.

Signs of a Bad Main Relay

It can be difficult for an ordinary car owner to diagnose such problems, but there are still a few basic things that owners and drivers can check to rule out common problems. The main relay is usually located under the dashboard, in the car’s fuse box, but it also depends on the make and model of the car:

1. The engine doesn’t start

As mentioned above, the main relay controls the fuel system. If the relay is faulty, it will not provide the power the fuel system needs, and if the vehicle is not receiving fuel, it will not start. Although there may be countless other, much more common factors that prevent the engine from starting, there may be times when the main relay proves to be the problem.

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Unfortunately, this is not an easy diagnosis and it can take some time to get to the relay. It is better to consult a mechanic for this task.

2. Check engine light is lit

A check engine light can greatly facilitate diagnosis with an OBD/OBD-II scanner depending on the year of manufacture of the vehicle. The code generated by the car’s computer can sometimes pinpoint the exact cause of the problem and even make it easier for owners to identify the problem. If you own a scanner and know how to use it, you can search for the code.

3. The car dies immediately after starting

If the car has difficulty staying running and dies shortly after starting, the main relay can be blamed for this as it supplies power to the car’s fuel system and the computer that constantly checks and balances the air-fuel intake and mixture ratio, which ensure that the engine runs smoothly.

4. The car sometimes starts, sometimes doesn’t

If your car does this, it could indicate that the relay sometimes works temporarily and fails at other times. This requires that you take care of the problem as soon as possible, as you might be stranded somewhere without a mechanic nearby, so it is better to see a mechanic if you notice this symptom.

5. The car fails to start when the interior has gotten hot

If you notice this, it is caused by the heat which moves the solder joints on the relay and ruins the circuit path. This is a recurring problem that must be solved immediately, as it can further damage the main relay if it is not checked in time.

There are a few things you can do to perform a surface diagnosis of the main relay that does not require any technical knowledge. This way you can determine if the main relay of your car is defective or has failed completely.

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What is the Main Relay?

A car needs an air-fuel mixture to drive, but to control the proportions of the mixture complex electrical switches are required, and a special computer must constantly check all these things to ensure smooth engine operation and a smooth ride, but often underlying electrical problems cause problems that won’t allow the car to start.

Likewise, it is unlikely that the main relay has become defective if a car refuses to start, but it is not impossible. To narrow down the exact problem, professional help is needed, as complex electrical systems can only be checked by certified mechanics with electrical knowledge and experience. A small mistake could render one of the most important electrical parts of a car unusable, so additional precautions are absolutely necessary.

Testing & Solutions

Diagnosing a faulty main relay can be difficult because many factors must be taken into account when the problem of the car not starting occurs. From fuel and air to the fuel pump and spark plugs, any one of these things can interfere with the normal operation of a car. If you are familiar with basic car knowledge, you can self-diagnose your car to a certain point until you find the problem.

Checking for the initial clicks upon starting the car

If you turn the key in 3 steps, the main relay clicks 3 times on different key positions. To check if the relay works on all levels of the key, place your hand on the relay and turn the key one level. You should hear a click. This only unlocks the ignition.

Turning the key again should turn on the electrical systems. The relay should give another click at this stage. Finally, the last stage starts the car, and the relay should also give a click. If the relay does not click at any point, there could be a problem.

Tap the relay

Sometimes tapping the relay causes it to function temporarily. If tapping the main relay causes the vehicle to start, the main relay is defective and must be repaired or replaced. Replacing the relay is not very difficult, but the repair requires electrical expertise.

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If you are not able to get your car going after checking all the basic things, the main relay is probably defective or there is an electrical problem that could have fried the main relay.

Main Relay Replacement Cost

The average cost of replacing the main relay can be over $200 depending on the car model and brand. To save the cost, you can also do the replacement at home.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

Comments
  1. hey there my friend I have a honda civic 2003 hybrid model but its been a bit modified the thing is that it turns on and runs but my battery light turns on the dash and after runing it for a bit it will power off and then come back on I replaced the battery relay but its not for my car they gave me one for a toyota it ran for a bit after I baught it but its now doing the same thing can it be that the battery is going out.

  2. Which goes first on a 04 accord the cube looking relay on the side of the driver panel or the one understeering column?

  3. 2001 honda civic lx will start but after warming up from driving then parked it will not start until it has set for a while then you can start it back up

  4. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
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