Signs of a Bad Starter Relay or Struggling Solenoid
March 9th, 2018
Updated: April 27th, 2021
Climb into your car. Buckle up for safety. Turn the key in the ignition and… nothing. Nothing but a click. The engine won’t turn over and your car won’t start. Could be a dead battery. But since the dash lights and the radio and the headlamps seem to be working, maybe something else is the culprit. This could be a sign that your car’s starter relay - or starter solenoid - has gone bad.
Relay vs. Solenoid
When you turn the key to start your car, you are activating the ignition switch. Like most of the switches in your vehicle, the ignition switch controls only a low-powered signal, in this case to start the engine. On older vehicles, the signal is an electrical current (like a light switch in your house); on newer vehicles, the signal may be an electronic impulse sent to the vehicle’s computer. In any case, the switch “tells” the starter circuit to engage.
But the starter itself requires a lot of power. Certainly more than the tiny wires running to the ignition switch can handle. The starter is tasked with the job of getting the internal parts of the engine turning, and that requires a lot of torque, thereby requiring more power. So automakers insert a device that enables a low-power signal to trigger a high-power signal. That way, a big job (like starting an engine) can be enabled by a small switch.
Both a relay and a solenoid are devices that receive a low-power signal as a trigger to close (or sometimes open) a much larger circuit with more power. In the case of a starter, the ignition switch signals the relay/solenoid (possibly by way of a computer) and the relay/solenoid switches on the starter circuit to engage the starter.
Now the terms relay and solenoid are often used interchangeably and there is a lot of confusion about which is which. (Hopefully we do not add to the confusion). While technically a relay and a solenoid are constructed and operate differently, both are remote electromagnetic “switches.” And both can perform the same function: control a high-power signal with a low-power signal. So, in that manner the terms are often used in place of one another. Because of its construction and manner of operation, a solenoid is usually capable of switching a higher current than a relay. Still, one person might refer to a starter relay and another to a starter solenoid.
Further muddying the water, these devices are located in different places on different vehicles. And some manufacturers use both a relay and a solenoid in the ignition system. In that case, the relay will trigger the solenoid. Most often, a true starter relay is a small black cube plugged into an electrical fuse/relay box in the engine compartment, whereas a starter solenoid is (in most cases) attached directly to the starter on the engine (although it is sometimes located elsewhere in the engine compartment).
Signs of a bad starter solenoid
Because it is more common to run into problems with the starter solenoid than with a plug-in relay, for our purposes we will focus on symptoms related to the solenoid. Consider these possible signs of a failing or bad starter solenoid when you turn the key:
1. Nothing happens. If you engage the ignition and it does nothing, there are a number of problems that could account. One possibility is the solenoid.
2. A single “click” sound comes from the engine compartment or from under the car. This could mean that the solenoid is trying to engage but that the internal components are stuck and unable to work properly.
3. Repeated “clicking” sounds usually indicate a dead battery. But a faulty solenoid that fails to make adequate electrical contact inside can also produce this tell-tale sound causing the battery to have low voltage unable to provide enough power to start your engine.
4. Sometimes a bad starter solenoid, instead of preventing the engine from starting, may cause it to start on its own without the key being turned to the “start” position.” This less-common problem can be dangerous and should be addressed immediately.
5. If the starter engages but does not disengage when you let go of the key, the solenoid is likely bad and the starter may suffer significant damage as a result.
6. Sometimes your car starts, sometimes it doesn’t. Intermittent operation can be a sign of a failing starter solenoid.
Other issues that present a bad solenoid
Problems that might cause your car to act like it has a bad starter solenoid can include:
Blown fuse - Sometimes the simplest explanation is the best one. A blown fuse in the starter circuit could be the cause of a no-start problem.
Broken or corroded wiring - Damaged or dirty wires to the battery or to the starter solenoid (or wires that are loose) can prevent sufficient power from reaching the starter.
Alternator -The alternator is designed to power all of your car’s electrical systems when the vehicle is running. It also recharges the battery. If the alternator is bad, the battery may not be capable of starting the engine.
Starter - Some solenoids are mounted to the starter, but some are located directly inside the starter housing. When this is the case, it may be necessary to replace the entire starter when the solenoid goes bad. Sometimes the starter itself is the problem.
Electrical issues can be annoying and inconvenient. They can also be hazardous and can cause damage. If you run into symptoms of a bad starter relay or solenoid with your car, truck, or SUV, make sure to have a trusted technician to diagnose the specific problem.