How to Test a Starter Relay
To test a starter relay, use a multimeter to check for continuity across the switching terminals and voltage at the power input terminal, then bypass the relay with a jumper wire; if the engine cranks when jumped, the relay is likely faulty. The starter relay is a small but critical link between your vehicle’s ignition switch and starter motor, and when it fails, the engine often won’t crank at all. This guide covers common bad starter relay symptoms, the tools you’ll need, a full step-by-step starter relay test, and what to do if testing points to a faulty relay.
Understanding the Role of a Starter Relay
Before testing a starter relay, it helps to understand what it does. Acting as an on-and-off switch, the relay controls the flow of electrical current from the battery to the starter motor when you turn the ignition key. This transition of power initiates the engine’s cranking process. When that process isn’t smooth, it’s time to assess the starter relay’s functionality.
Signs of a Bad Starter Relay
A handful of symptoms typically point to a failing starter relay before you even pick up a multimeter:
- A single click with no crank. You hear the relay engage, but the starter motor doesn’t turn the engine over.
- No click and no crank. Turning the key produces no sound and no response from the starter system at all.
- Intermittent starting problems. The vehicle starts fine sometimes and not others, with no clear pattern.
- A relay that feels warm or shows signs of overheating. Discoloration or a burning smell near the relay can indicate internal damage.
- Normal accessories, but no crank. Dashboard lights, radio, and other accessories work fine, which points toward the starting circuit rather than the battery.
If you’re seeing one or more of these symptoms, testing the relay is a reasonable next diagnostic step.
Tools You’ll Need for Testing
To begin testing, gather the following:
- A digital multimeter
- A jumper wire
- Basic hand tools
Checking a Starter Relay Safely
A few precautions apply before and during testing:
- Set the parking brake and keep the vehicle in park or neutral before any test that involves cranking the engine.
- Use insulated tools and avoid touching multiple terminals at once when the circuit is powered.
- Only energize the circuit for the specific checks described below, and remove the key from the ignition between steps that don’t require power.
- These are general diagnostic steps. If you’re not comfortable working near a vehicle’s electrical or starting system, have a qualified technician confirm the diagnosis before replacing any components.
How to Test a Starter Relay: Step-by-Step
Follow these steps to check the functionality of a starter relay:
- Locate the relay. Typically housed in the engine compartment’s fuse box, the starter relay is identifiable as a small, square or rectangular component with multiple pins. Check the fuse box diagram, usually printed on the inside of the fuse box cover, if you’re unsure which relay it is.
- Try the swap test. If another relay in the fuse box shares the same part number as the starter relay (check the number printed on each relay’s case), swap the two and try to start the vehicle. If it starts, the original relay was likely the problem. If it doesn’t, move on to the tests below. This check requires no tools.
- Perform a visual inspection. Look for visible damage, corrosion, or loose connections that could affect the relay’s performance.
- Remove the relay and test continuity. Pull the relay from its socket before testing on the bench; testing while it’s still seated can give false readings from other paths in the fuse box. Set the multimeter to continuity or resistance mode. On a standard 5-pin relay, the coil terminals are typically labeled 85 and 86, and the switched load terminals are typically labeled 30 and 87. Test across 85 and 86 to confirm the coil circuit isn’t broken, then test across 30 and 87, which should show no continuity at rest.
- Test coil resistance. With the relay still removed, set the multimeter to resistance mode and measure across the coil terminals (85 and 86) to check for an open or shorted coil.
- Check for power. Set the multimeter to DC voltage mode, then check for voltage at the relay socket’s power input terminal with the ignition on, confirming it’s receiving the necessary electrical input.
- Jump the relay socket. With the relay still removed, briefly connect a jumper wire between the socket’s load terminals (30 and 87) to bypass the relay directly. If the engine cranks, the relay itself is likely faulty. See the section below for more detail on this step.
How to Jump a Starter Relay
Jumping a starter relay bypasses the relay itself to confirm whether the starter motor and its wiring are functioning correctly. With the relay removed from its socket, use a jumper wire rated for the circuit’s current to briefly connect the socket’s load terminals, typically labeled 30 and 87 on a standard 5-pin relay. With the parking brake set and the vehicle in park or neutral, make the connection briefly. If the engine cranks when jumped, the starter motor and wiring are functioning and the relay is the likely point of failure.
Replacing a Faulty Starter Relay
After completing these tests, review the results together. A lack of continuity, missing voltage at the power input, no response to jumping, or coil resistance outside expected behavior all point toward a relay that needs replacing. Starter relays are available for a wide range of vehicle makes and models. If testing points to a faulty relay, our team can help you source the right replacement part or the battery and starter cables needed to complete the repair.
Need Parts for Your Starting System?
Gateway Cable Company supplies connectors, cable assemblies, and power distribution components to support a wide range of electrical projects, including starter and battery cable work. If testing points to a faulty relay or you need related parts, our team can help.
Frequently Asked Questions
How do you test a starter relay?
To test a starter relay, try swapping it with an identical relay elsewhere in the fuse box, then remove it to check continuity and coil resistance, confirm voltage at the socket’s power input terminal, and bypass it with a jumper wire across the socket. If the engine cranks when jumped, the relay is likely faulty.
How do you check a starter relay with a multimeter?
Remove the relay from its socket, then set the multimeter to continuity or resistance mode to test the coil terminals (typically labeled 85 and 86) and the switched load terminals (typically labeled 30 and 87), which should show no continuity at rest. Reinstall the relay and switch the multimeter to DC voltage mode to confirm the socket’s power input terminal is receiving voltage with the ignition on.
What are the symptoms of a bad starter relay?
Common bad starter relay symptoms include a clicking sound with no engine crank, no click and no crank at all, intermittent starting problems, or a relay that feels warm or shows signs of overheating. Dashboard lights and accessories typically still work normally even when the starter relay has failed.
What does a starter relay test involve?
A starter relay test typically starts with a swap test using an identical relay from elsewhere in the fuse box, followed by a visual inspection, a continuity and coil resistance check with the relay removed, a voltage check at the socket’s power input terminal, and a jumper wire bypass test.
What happens if you have a bad starter relay?
A bad starter relay usually prevents the starter motor from engaging, so the engine won’t crank even though the battery and other electrical components are working normally. In some cases, a failing relay causes intermittent starting issues or a clicking sound without the engine turning over.
Need help sourcing a replacement starter relay or the cables to go with it? Gateway Cable Company supplies connectors, cable assemblies, and power distribution components for a wide range of electrical projects. Contact us for a quote, or browse our cable assembly and power components.