There are several possible reasons why a car can fail to start, ranging from a failed ignition switch, a bad starter, loose connections, and a weak or bad battery.
One possible cause of a failed start that is often overlooked is a bad car starter relay.
In this post, I’ll cover what a car starter relay does, reasons why it can fail, tests you can perform to check if it is bad or not with suggestions of fixes.
What is the Starter relay?
This relay is part of the starter circuit and helps ensure that the car only starts when the gear shifter is in the parking or neutral positions in automatic vehicles and for manual transmission vehicles when the clutch is pressed.
The starter relay is located in the fuse box under the hood of the car.
It is connected between the safety switches above and the magnetic solenoid switch on the car starter and only activates power to the starter when the safety switches are in the recommended safe positions,i.e. parking or neutral for automatic and clutch depressed in manual transmission vehicles.
Can a Starter Relay Go Bad?
Yes, a car starter relay can fail. When it does, it is not able then to activate the car starter and start the engine when the ignition is switched to the START position.
A failed car starter relay may have shorting or open contacts that fail to supply the necessary 12V to the car starter.
What happens when a starter relay is bad
When you turn the ignition key to the START position when the car starter relay has failed, you will usually hear a clicking sound only, the car does not crank or start!
Causes of Car Starter Relay Going Bad
While some car starter relays can last a long time, others fail much sooner. Common causes of failure of the starter relays are:
Age of the relay. Over time as the contacts open and close, the relay mechanisms can fail from the wear and tear of over the years.
In some cases, excessive current draws by the car starter motor can damage the car starter relay.
Symptoms of Bad Starter Relay
You can tell that the car has a bad starter relay or one about to fail when:
Car fails to start completely
You turn the ignition to the START position and all you hear is the clicking sound. The engine does not crank or start yet the car battery is charged and the battery connections are clean and make firm contact.
Intermittent failure to start problem
In another case, the car engine can fail to start on the first but then starts successfully after several attempts of turning the ignition key. This might be a case of the starter relay about to fail.
You may want to read: Bad Car battery Vs. Bad Car alternator – how to tell the difference
How to Test a Car Starter Relay
To check if the car starter relay is still good, you can conduct the following tests:
You can test whether the starter relay contacts open or close with a good quality digital voltmeter when you turn the ignition key to the START position and release it.
You can also check that the starter relay coils receive 12V DC from the battery by checking the voltage between the battery ground and one of the terminals of the car starter coil.
Also, you can narrow the fault to the starter relay if the car starter can crank and starter the car engine when you supply it directly with 12V from the battery (bypassing the starter relay).
Another way is to test and measure the voltage at the car starter solenoid with the ignition key turned to the START position. Note, the gear shifter should be in the parking or neutral position for automatic cars and clutch pressed for manual transmission circuits.
If there is no voltage measured, then there is a problem with the starter relay or the wiring.
Note: requires a good understanding of car electrical system wiring – do not attempt if you do not have the skills.
How to Fix a Bad Starter Relay
If the car has a bad starter relay, it is best that you replace it with a new one that fits the recommendation of the OEM.
A car starter relay is usually connected between the ignition switch and the car starter and essentially checks that the parking/ neutral safety switches (automatic cars) and clutch switch (manual cars) are engaged before the car can be started.
They usually fail on their own and when they do, the car simply clicks and fails to crank let alone start.
The recommended fix is to replace the faulty relay with one that is recommended by the manufacturer.