How to Check a Starter Solenoid or Remote Relay
To check a starter solenoid, you can use a digital multimeter and a few common tools.
Basically, a starter solenoid works just like a regular relay: It acts as a switch that uses a small current to control a higher current that energizes the starter motor.
You may suspect a bad starter solenoid if you can hear a single, loud click when trying to start the engine. Still, a starter motor can fail in other ways and produce different symptoms due to an electric current resistance, loose wires or bad grounds. So don't blame the solenoid just yet.
Starter solenoids come in two types: On-starter configuration — most solenoids — and as a remote type relay — used on many Ford vehicle models and some other models. With an on-starter solenoid, you'll probably need to remove one or more components or lift your vehicle to gain access to the solenoid for the next tests. Testing a remote-type solenoid — aka starter relay — works relatively faster because of its physical location near the car battery on the fender well.
So let's start the tests.
Tools you'll need:
Set of wrenches, if you need to move components
Ratchet and socket set, if you need to move components
Small jumper wire
How to Check the Solenoid
Before you start these tests, make sure you have a charged battery. Then, set your transmission to Neutral and disable the ignition system. You can do this by removing the fuel pump fuse or relay, or by disconnecting the ignition coil from the distributor cap — if your engine has it — and grounding the coil wire with a jumper wire. This will prevent the starter motor from accidentally starting the engine during your tests.
Testing the starter solenoid electric ground:
1. Open the hood and locate the solenoid — the small cylinder on top of the starter motor. A remote-type relay, sits usually near the battery, on the fender well, and the red battery cable connects directly to it.
2. Ask an assistant to turn the ignition key to the start position — as if starting the engine — while you listen to the solenoid. If you can hear a strong click coming from the solenoid, continue with the rest of the steps in this section. If the solenoid or relay produces a weak click, chattering sound or no sound at all, go on to the next section, Checking for Current Resistance.
3. Let's check for voltage drop.
* Set your multimeter to 15 or 20 volts on the DC Voltage scale.
* Touch the red wire (battery) connection on the solenoid with the red meter probe, and the other main connection that has a small strap going to the starter motor (no wire). On a remote relay, this is the connection with the thick black wire.
* Turn on the meter and ask your assistant to turn the ignition key to the start position.
* You should get a voltage drop of around 0.2 volts or less. If your reading exceeds this voltage, disconnect those wires from the solenoid or relay and remove corrosion, grease or dust using a wire brush. WARNING: Disconnect the battery negative (black) cable first, before cleaning the wire terminals on the solenoid or you make cause a strong electric short and seriously burn your hands.
* Reconnect the wires and the battery negative cable.
* Check for drop voltage again. If you still get over 0.2 volts, replace the starter solenoid.
* Includes protective boot, detachable color-coded test leads and alligator clips
* Automatic zero adjustment for volts and amps for accurate measurements
* Automatic reverse polarity indication
* Overload protection on all ranges and fold-out stand for better viewing
* 1-year warranty
Checking for Current Resistance
The solenoid also has a thin wire connected to it. This is the ignition switch connection, usually marked "S", and it's referred to as the control circuit. This connection only has current when you turn the ignition key to the Start position, when cranking the engine to start it.
1. If you heard a weak click, chattering sound or no sound at all coming from the solenoid as your assistant turned the ignition key to the Start position in the previous section, disconnect the control circuit wire and check the connector for corrosion or looseness.
* Also on a remote-type solenoid, check for dirt or corrosion between the solenoid mounting bracket and the mounting surface.
* The mounting bolts should be tight.
* Also on a remote-type solenoid: Set your meter to the Ohms scale and check for resistance between the control circuit terminal and the solenoid's mounting bracket. If you get more than 5 Ohms, replace the solenoid.
2. Connect a jumper wire between the control circuit terminal and the battery wire terminal on the relay or solenoid.
* You should hear a solid click, indicating the solenoid is operating properly; if you hear a weak click, a chattering sound, or nothing, and you're positive you have no loose connections and no corrosion or dirt between the connectors and wires, replace the solenoid.
3. Now, check for voltage at the control circuit — this should confirm your results in the previous step.
* Remove the jumper wire from the control circuit connector.
* Touch the control circuit wire with your meter's red probe, and the relay metal case or starter motor metal case with the meter's black probe.
* Ask your assistant to turn the ignition key to the Start position.
* If there's voltage (12V or more), replace the solenoid. Otherwise, check for an open in the ignition side of the circuit.
The following video can help you identify the solenoid wiring connections if you need some visual help.
When you need to check a starter solenoid or remote relay, using the systematic approach outlined here will help you find the source of the fault much faster. Sometimes, you'll find that a corroded terminal, loose wire or a different component is behind the fault. Other times, you'll discover that your solenoid or relay has reached the end of its service life. Whatever the cause, this procedure will help you save time and money and get your car back on the road sooner. If you need to replace the solenoid or relay, you'll spend between $10 and $30 dollars, depending on your vehicle model. You can buy one at your local auto parts store or online.
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