A bad or failing main relay can cause a number of problems for your vehicle. Both the fuel system and your vehicle’s powertrain control module (PCM) are connected to the main relay, and it can affect both if it goes bad. While the main relay is meant to last for your vehicle’s lifetime, it can still fail in rare cases. But how will you know it’s the main relay to blame?
Symptoms of a Bad Main Relay
When your vehicle’s main relay fails, you’re likely to notice the following symptoms:
Vehicle Won’t Start
A bad main relay will often lead to your vehicle not starting altogether. Remember that a dead battery or a bad starter are more common causes of this symptom, so be sure to rule those two out first.
The Vehicle Ignition Is Unreliable
Sometimes, a malfunctioning main relay will become more unreliable instead of failing completely. The relay will work one moment and then stop working suddenly. This can be dangerous because it can easily leave you stranded if the relay stops working out of the blue. If you notice that starting your vehicle becomes more like Russian roulette, it’s best to call a mechanic as soon as possible to diagnose if it’s a problem with the main relay.
The Vehicle Won’t Stay Running
A bad main relay will sometimes lead to your vehicle not running for very long. If you’re able to start the vehicle, it might stop running in a matter of seconds or minutes. The engine will stop running, and your vehicle won’t move or start.
Main relay problems could also lead to your engine running for a while or a very short time. Your vehicle might start normally sometimes but not start at all at other times.
Illuminated Check Engine Light
Not being able to start your vehicle will often lead to the check engine light being lit on your dashboard. A mechanic with the proper diagnostic tools will be able to identify if the main relay is the problem behind the check engine light.
How Does a Main Relay Work?
Relays work somewhat like switches, but they’re operated through a type of remote control. They are, in essence, simple electromechanical switches. Normal switches connect or break paths in a circuit to control electric currents. Relays do the same thing, but they instead connect or break these paths using a small coil that can be energized or de-energized by another switch elsewhere in the system. That switch is the relay’s “remote control.”
The main relay acts like most other relays, but it specifically connects and controls the fuel system and the PCM. The relay turns on and activates both these systems when you turn your key in the ignition.
Where To Find the Main Relay
You can find the main relay in your vehicle’s fuse box, which is commonly found under the passenger side dashboard or the engine bay. The fuse box cover will usually show a diagram of the box’s different fuses and relays. You can find the exact location of the main relay either on this diagram or in your vehicle’s owner’s manual.
On Ford vehicles, there’ll only be a diagram with all the fuses and relays numbered. You have to use the owner’s manual to find the fuse location and the breakout of the box. This information might also be available online.
Replacement Cost of a Main Relay
Buying a replacement main relay will run you anywhere from $10 to $180 depending on the make and model of your vehicle. These bad main relay symptoms can undoubtedly affect how your vehicle starts and runs, so try to get your main relay fixed as soon as possible if it’s acting up.
Replacing Your Vehicle’s Main Relay
If your vehicle has a failed main relay, it may become unreliable and not start at all. Fortunately, it’s not too difficult to find a replacement that’s compatible with your vehicle thanks to CarParts.com.
The best part? You can get your hands on a new relay without ever leaving your house. Simply use your mobile phone or computer to visit CarParts.com. Use our vehicle selector and input your vehicle’s details. Make sure to input the exact year, make, model, and engine.
We make it a point to get our auto parts from some of the most trusted manufacturers in the industry. In addition, our warehouses are located all over the US, meaning you can receive your order within days.
Check out our selection of quality parts now at CarParts.com.
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