12 Most Common Symptoms Of A Bad Main Relay

Written By: Terrence Hines
Category: Engine

Symptoms of a bad main relay include difficulty starting the engine, dim or flickering lights, stalling, and electrical components not responding correctly.

If you’re experiencing any of these symptoms, it’s important to get your main relay checked as soon as possible to understand the cause of the issue.

Symptoms Of A Bad Main Relay – 12 Most Common Ones!

A bad main relay in a vehicle can be very bad. This is because the main relay powers every car’s electrical system. So, if it fails, the car might stall, have surged, or not start at all.

The main relay is located near the battery or dashboard. It can burn out if too much electricity goes to it at one time.

This happens when multiple components turn on simultaneously, there is too much voltage or the wires next to it are corrupted or shorting.

Test all power connections before replacing the part to diagnose a bad main relay.

If you think there is something wrong with your car’s relay, it is best to take it to a mechanic. They will figure out what is wrong and fix it so your car will work again.

Here are some signs that there might be something wrong with the main relay:

1. Engine Won’t Start:

If your engine doesn’t start, the symptom may be caused by a bad main relay.

A main relay is an electro-mechanical switch that directs power from the battery to the starter, allowing your engine to turn over and start.

Symptoms Of A Bad Main Relay - 12 Most Common Ones!

It also handles other circuits, such as the fuel pump and ignition. If this is not working correctly or has failed, it can cause issues with starting your vehicle.

To test for a faulty relay, locate it in the fuse box, use a multimeter to check for voltage and current at the terminals, or use an ohm meter if necessary.

If you identify that the main relay is causing trouble, it should be replaced immediately; otherwise, you could end up stuck with no way to get home.

2. Dashboard Warning Lights Coming On:

No one likes seeing dashboard warning lights come on all of a sudden, particularly when there appears to be no cause. The symptom may indicate that your main relay is going bad.

A main relay’s responsibility is to regulate power distribution to various modules in the car, such as the radiator fan, air conditioner, and even the fuel pump.

That’s why it’s essential to check out this symptom as soon as it occurs and fix the problem before any further damage occurs.

If you do not know what to do or where to find the main relay for your car, ask a professional mechanic. They can help you determine why the dashboard lights appear without warning.

3. Weird Noises When The Engine Is Running:

If you’re hearing an abnormal sound from the engine while it’s running, this could be one of the symptoms of a bad main relay.

Main relays can experience wear and tear over time and eventually fail, resulting in a faulty connection between the car battery and the electrical system.

This symptom may initially be subtle until its consequences become more exaggerated as the breakdown progresses.

In addition to strange noises from the engine, you may also notice issues with starting your car, periods of stalling, and sudden drops in vehicle performance.

If you suspect that your main relay has gone wrong, it’s best to have a professional diagnose and replace it to prevent further damage.

4. Car Refusing To Go Into Gear:

If your car suddenly refuses to go into gear, a symptom of a bad main relay could be the cause. Therefore, acting quickly and getting it addressed as soon as possible is important.

Car Refusing To Go Into Gear

A bad main relay can sometimes be detected by looking for a clicking sound when you turn on your ignition switch or pushing in certain buttons in succession.

If any of these symptoms coincide with your car not going into gear, it is likely time to replace the main relay and restore its ability to shift correctly.

If left unchecked, this symptom could lead to other mechanical failures within your vehicle that could require costly repairs down the road.

5. Ac Or Heating Not Working Properly:

If you’re having trouble with the air conditioning (AC) or heating in your vehicle not working properly, one symptom of a bad main relay could be to blame.

A main relay is an electrical component that helps control and regulates power flowing to the AC compressor or blower motor.

If the main relay has failed, it can cause the systems to either not work at all or have intermittent operation problems.

Common symptoms of a failing main relay are an AC system that blows irregularly cold air, sporadic heater operation with no hot air blowing through the vents, or no AC/heater operation.

Replacing the faulty main relay should resolve any issues and restore the proper functionality of your vehicle’s heating and cooling systems.

6. Radio, Headlights, And Other Electrical Features Not Working:

If you notice symptoms such as your radio, headlights, and other electrical features failing to work correctly in your vehicle, you’re likely experiencing a bad main relay.

Moreover, common symptoms of a bad main relay include difficulty starting your engine, water seeping out from the area around it, and difficulty with electricals and headlights.

If you’re facing any of these symptoms, it’s important to recognize them quickly and have the main relay checked by a professional or replaced entirely.

Otherwise, the issues could worsen over time, leading to more costly repairs.

7. Vehicle Stalls While Driving:

Driving a vehicle is a comfortable and convenient way to get from Point A to Point B.

Symptoms Of A Bad Main Relay

But, a stalled vehicle can be a major disruption and a sign of a larger problem. Vehicle stalling while driving often comes under the symptoms of a bad main relay.

The main relay works with the fuel system to provide electrical power for the starter motor and ignition system and acts as a “gatekeeper.”

If this relay is damaged or corrupted, it can cause the vehicle to stall during a drive.

When this happens, it is important to get the car looked at by a qualified mechanic to diagnose any other underlying problems.

8. Engine Overheats:

One symptom of a bad main relay is a vehicle’s engine overheating.

This malfunction causes an engine to run hot even after a cool-down period continuously, and a vehicle will start to experience damage to its components.

If a car owner suspects a bad main relay, they should not attempt to drive the car further and should take it to a qualified service technician to diagnose the issue.

Replacing the main relay can fix the issue and return the vehicle to working order.

9. Car Won’t Crank:

A bad main relay can often cause a car not to crank when the ignition key is turned.

This issue can also be a symptom of a breakdown in one or more components of a vehicle’s electrical system, setting off a chain reaction.

Before replacing the main relay, it’s important to diagnose and inspect the other relevant vehicle electrical parts properly.

If the car doesn’t start, it might be because of the main relay. Check if the main relay is causing the problem before looking at other parts that could be to blame.

10. Hesitation When Starting The Engine:

When a vehicle’s main relay is in a state of disrepair, it can cause various problems while starting the engine. One common symptom is hesitation before the engine starts.

If your car hesitates a moment before starting, it could be because the main relay is bad.

The main relay helps send power from the battery to your car’s ignition system. Luckily, this part is easy to replace.

It’s a good idea to have your mechanic inspect if you experience hesitation when starting your car, as it could save you money and grief down the road.

11. Rough Running Engine:

When driving, one symptom of a bad main relay is a rough-running engine.

The main relay regulates the power and current sent from the battery to the engine. Without it, your car will not start or run efficiently.

If you’re experiencing a rough-running engine, it’s important to determine if a bad main relay is a culprit.

To do this, you’ll want to inspect the electrical connections associated with the relay and test its functions with an ohmmeter.

Be sure to replace any faulty or worn parts before returning your vehicle to the road.

12. Bad Fuel Economy:

Bad fuel economy is a symptom of a bad main relay, which can occur if the main relay becomes damaged or corrupted.

The main relay helps to control the fuel system. This includes when fuel is injected into the engine. It also controls other things related to starting the vehicle.

So, if you notice this symptom, it might be a sign that something is wrong with your car’s performance.

Replacing a bad main relay can address poor fuel economy and restore optimum performance to your vehicle.


Symptoms of a bad main relay should be addressed as soon as they manifest.

It’s essential to bear in mind that although the car may have difficulty starting its engine, faulty headlights, or a tendency to stutter, these signs could also be caused by some other problems.

The best way to determine if the problem comes from a bad main relay is to take the car to an experienced mechanic for testing and diagnosis.

Taking care of this problem promptly can save time and money, as ignoring it can lead to further electrical damage in your vehicle.

Terrence Hines

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