When your power door locks stop working properly maybe only one lock responds, or none of them do at all the relay is one of the first things worth checking. A door lock relay is a small electrical switch that sends power to the lock actuators when you press the button. Testing it with a multimeter takes about ten minutes, costs nothing if you already own the tool, and can save you from replacing parts that are still good. This guide walks you through the exact process, so you can find the problem and fix it with confidence.

What Is a Door Lock Relay and How Does It Work?

A door lock relay is an electromagnetic switch tucked inside your car's door lock circuit. When you press the lock or unlock button on your key fob or interior switch, the relay receives a small signal and uses it to close a larger circuit. That larger circuit delivers the higher current needed to activate the door lock actuator the motor that physically moves the lock mechanism up and down.

Relays are common in most vehicles from the mid-1990s onward. They're usually located in a fuse box under the dashboard, behind a kick panel, or in the engine bay. Your owner's manual or a wiring diagram for your specific vehicle will show the exact position.

When a relay fails, the symptoms often look like a dead actuator or a bad switch. That's why testing the relay first makes sense it's the quickest way to rule out or confirm a failure before pulling apart door panels.

What Tools Do You Need Before You Start?

You don't need anything expensive or specialized. Here's what to gather:

• A digital multimeter capable of measuring resistance (ohms), continuity, and DC voltage. A basic model from any hardware store works fine.
• Your vehicle's wiring diagram or owner's manual to locate the relay and identify the pin layout.
• A small flathead screwdriver or relay puller to remove the relay from its socket.
• A 12V test light (optional) for a quick second check on voltage at the relay socket.
• A clean, dry workspace with good lighting under the dash or at the fuse box.

Where Is the Door Lock Relay Located?

The location varies by vehicle. On most cars, the door lock relay sits in one of these spots:

• Under the dashboard on the driver's side, inside a junction box or fuse panel.
• Behind the kick panel near the driver's left foot.
• Under the hood in the main fuse and relay box.
• Integrated directly into the body control module (BCM) on newer vehicles.

Check your owner's manual first. If you don't have a physical copy, many manufacturers offer free PDF versions online. You can also find relay location diagrams on AutoZone's repair guides. Look for the relay labeled "Door Lock" or "D/LCK" on the fuse box cover diagram.

How to Test a Door Lock Relay With a Multimeter Step by Step

Step 1: Locate and Remove the Relay

Turn the ignition off. Find the door lock relay in the fuse box and pull it straight out using a relay puller or a small flathead screwdriver. Be gentle prying too hard can crack the socket or damage surrounding connectors.

Step 2: Identify the Relay Pins

Most standard automotive relays have four or five pins. Look at the bottom of the relay for a small diagram printed on the casing. You'll typically see labels like:

• 85 – Coil ground
• 86 – Coil power (signal input)
• 30 – Common terminal (power input to the switch side)
• 87 – Normally open (NO) terminal
• 87a – Normally closed (NC) terminal (on 5-pin relays)

These numbers follow a standard numbering system used across the automotive industry. If your relay doesn't show the diagram, search for the part number printed on it to find a pinout.

Step 3: Test the Coil Resistance

Set your multimeter to the ohms (Ω) setting. Place one probe on pin 85 and the other on pin 86. These are the coil terminals.

A healthy relay coil should read between 50 and 120 ohms, depending on the relay. If the reading shows OL (open loop) or infinite resistance, the coil is burned out and the relay needs replacement. A reading near zero ohms means the coil is shorted also a failed relay.

Step 4: Check Continuity on the Normally Closed Pin

Without applying any power to the relay, move your multimeter probes to pin 30 and pin 87a. Set the meter to continuity mode or low ohms.

You should hear a beep or see a reading close to zero ohms. This means the normally closed contact is intact when the relay is at rest. If there's no continuity, the internal switch contacts are worn or corroded.

Step 5: Confirm the Normally Open Pin Is Open

Now place the probes on pin 30 and pin 87. With no power applied, these should not have continuity. Your multimeter should show OL (open). If you get continuity here while the relay is de-energized, the contacts are stuck closed a sign of a welded or damaged relay.

Step 6: Energize the Relay and Re-Test

This is where you confirm the relay actually clicks over when it receives power. You have two options:

Option A – Bench test with a 12V source: Connect 12 volts from a battery or bench power supply to pins 85 and 86 (positive to 86, negative to 85). You should hear a distinct click. While energized, check continuity between pins 30 and 87. It should now read near zero ohms (closed circuit). The reading between 30 and 87a should now show OL (open circuit).

Option B – In-vehicle test: Reinstall the relay into the socket. With the ignition on, use your multimeter to check for voltage at pin 87 (the output to the actuator) while pressing the lock or unlock button. If voltage appears at pin 30 but not at pin 87 when the button is pressed, the relay isn't switching.

Step 7: Test Voltage at the Relay Socket

If the relay tests good out of the car but the locks still don't work, the problem may be upstream. Set your multimeter to DC volts. With the relay removed, probe the socket terminals for pin 30 (you should see ~12V with the ignition on) and pin 86 (you should see ~12V briefly when you press the lock button).

No voltage at pin 30? Check the fuse. No voltage at pin 86 when pressing the button? The issue is in the switch, the wiring, or the body control module not the relay.

What Do the Multimeter Readings Tell You?

Test	Good Relay	Bad Relay
Coil resistance (85 to 86)	50–120 Ω	OL or near 0 Ω
NC contact (30 to 87a), no power	Near 0 Ω (beep)	OL no continuity
NO contact (30 to 87), no power	OL open	Near 0 Ω stuck closed
NO contact (30 to 87), energized	Near 0 Ω (beep)	OL not switching
Voltage at socket, pin 30	~12V with ignition on	0V check fuse or wiring

What Are the Most Common Mistakes When Testing a Door Lock Relay?

Getting this wrong can send you chasing the wrong part. Watch out for these errors:

• Testing the wrong relay. Many fuse boxes have multiple relays that look identical. Double-check the diagram on the fuse box cover to confirm you're pulling the door lock relay, not the horn or accessory relay.
• Forgetting to turn the ignition off before removing the relay. Pulling a relay under load can cause a small spark or damage the socket contacts over time.
• Only testing the coil and skipping the contact test. A relay can have a perfectly good coil but burned-out contacts inside. Always test both the coil resistance and the switching function.
• Assuming a click means the relay is good. A relay can click audibly but still fail to carry current if the internal contacts are corroded or pitted. The multimeter test is more reliable than listening for a click.
• Ignoring the socket and wiring. A relay that tests good on the bench but doesn't work in the car points to a problem with the socket, fuse, ground connection, or wiring harness not the relay itself.

If your relay tests good but only one door lock works in one direction, the issue may actually be with the door lock switch working in only one direction, which has its own set of causes worth checking.

What Should You Do After Testing the Relay?

Based on your results, here's what to do next:

• If the relay failed any test: Replace it with an OEM-equivalent relay matching the same part number and pin configuration. Generic relays from auto parts stores work fine as long as the pin layout and coil voltage match.
• If the relay passed all tests: Reinstall it and move your diagnosis to the door lock actuator, the switch, or the wiring. A faulty actuator is a common next suspect especially if you hear the relay click but the lock doesn't move.
• If the socket has no voltage: Check the door lock fuse first (usually a 15A or 20A blade fuse). Then inspect the wiring between the fuse box and the relay socket for corrosion, loose pins, or broken wires.

For a deeper look at actuator issues where the lock works one way but not the other, we cover the actuator that locks but won't unlock in a separate diagnosis walkthrough.

Can You Test a Door Lock Relay Without Removing It?

You can do a partial test without pulling the relay. With the relay still in its socket and the ignition on, use the multimeter to check for voltage at the output side (pin 87 circuit) while someone presses the lock button. If you see 12V appear and disappear with the button press, the relay is switching.

This in-circuit voltage test is fast, but it won't tell you about coil resistance or contact condition. For a complete diagnosis, pulling the relay and testing it on the bench is still the better approach. A full door lock relay testing walkthrough covers both methods if you want a more detailed reference.

Quick Checklist Before You Wrap Up

• ✔ Locate the correct door lock relay using your fuse box diagram
• ✔ Remove the relay with the ignition off
• ✔ Identify pin numbers (85, 86, 30, 87, 87a)
• ✔ Measure coil resistance between pins 85 and 86 (expect 50–120 Ω)
• ✔ Check NC continuity between 30 and 87a with no power (expect beep)
• ✔ Confirm NO is open between 30 and 87 with no power (expect OL)
• ✔ Energize the coil with 12V and verify 30-to-87 continuity switches on
• ✔ Test voltage at the socket if the relay passes but locks still fail
• ✔ Replace the relay if any test fails, or move diagnosis to the actuator and wiring

Keep your multimeter and this checklist in mind any time your power locks act up. Testing the relay first usually saves you the time and cost of pulling a door panel apart for no reason.