Can AutoZone Test Relays? | Test Smart, Fix Fast

AutoZone stores generally do not have dedicated equipment to test automotive relays, but checking them at home is straightforward with basic tools.

There’s a lot going on under the hood and dash of your car. Many small components work tirelessly to keep everything running smoothly.

Among these unsung heroes are automotive relays, tiny but mighty electrical switches.

When something goes wrong, you might wonder about testing these parts. Let’s talk about relays and how to check them.

The Unsung Heroes of Your Car’s Electrical System

Relays are like remote-controlled switches in your car’s electrical system. They allow a low-current circuit to control a high-current circuit.

This protection keeps delicate switches from burning out. Think of it as a traffic cop directing heavy electrical flow.

They are essential for many critical functions.

Your car uses relays for components that draw significant power. This includes headlights, the fuel pump, horn, starter motor, and air conditioning clutch.

When you turn on your headlights, a small signal from the switch activates a relay. That relay then sends a strong current directly to the lights.

Relays can fail over time due to constant use, heat, or corrosion. A faulty relay can cause anything from a minor annoyance to your car not starting.

What Makes a Relay Click?

Inside a standard relay, there’s an electromagnetic coil and a set of contacts. When power flows through the coil, it creates a magnetic field.

This magnetic field pulls a metal arm, closing the contacts. That’s the “click” you often hear.

This action completes the high-current circuit. It’s a simple yet incredibly effective design.

Can AutoZone Test Relays? Understanding Their Services

Many drivers head to their local parts store for help with diagnostics. AutoZone offers several free testing services that are very helpful.

They can test your car’s battery, starter, and alternator right on the vehicle. They also provide free OBD-II code scanning.

However, when it comes to individual automotive relays, AutoZone stores typically do not have specific equipment to test them.

Their diagnostic tools focus on larger, more complex systems. Relays are generally considered simpler components to test.

The variety of relay types and pin configurations also makes a universal testing machine less practical for them. Most relays are simple enough for a DIY check.

While they won’t test your relay directly, their free code scanning can still be useful. A trouble code might point to a circuit that uses a relay, giving you a starting point.

For instance, a “P0230 Fuel Pump Primary Circuit Malfunction” code could suggest a problem with the fuel pump relay.

Knowing the code helps narrow down the possibilities. Then you can test the specific relay at home.

DIY Relay Testing: Tools and Techniques

Testing a relay yourself is a straightforward process. You only need a few inexpensive tools.

This quick check can save you time and money on unnecessary part replacements.

Tools You’ll Need:

• Digital Multimeter: Essential for checking resistance and continuity.
• 9-Volt Battery: Or a 12-volt power source from your car battery with jumper wires.
• Jumper Wires: With alligator clips are ideal for making connections.

Understanding Relay Pins

Most automotive relays have four or five pins. These pins are usually numbered or labeled on the relay casing.

• Pin 85 & 86: These are the coil terminals. When power is applied here, the relay “clicks.”
• Pin 30: This is the common power input terminal for the switch.
• Pin 87: This is the normally open (NO) output terminal. Power flows from 30 to 87 when the coil is energized.
• Pin 87a: Found on 5-pin relays, this is the normally closed (NC) output terminal. Power flows from 30 to 87a when the coil is NOT energized.

Testing a 4-Pin Relay (Normally Open)

1. Visual Inspection: First, look for any signs of damage, such as burn marks, corrosion on the pins, or a cracked casing.
2. Test Coil Resistance: Set your multimeter to measure ohms (Ω). Touch the probes to pins 85 and 86. You should get a reading between 50 and 150 ohms. If it’s infinite (open circuit) or zero (short circuit), the coil is bad.
3. Apply Power to Coil: Connect the positive terminal of your 9V battery (or 12V source) to pin 85 and the negative to pin 86. Listen for a distinct “click.” This confirms the coil is activating.
4. Test Switch Continuity: While power is still applied to the coil (and you hear the click), set your multimeter to continuity mode (or ohms). Touch the probes to pins 30 and 87. You should hear a beep or see a very low resistance reading (near 0 ohms). This indicates the switch contacts are closing.
5. Remove Power: Disconnect power from pins 85 and 86. The relay should “unclick.” Now, test continuity between pins 30 and 87 again. You should get an open circuit (no beep, infinite resistance).

Testing a 5-Pin Relay (Normally Open/Closed)

The process is similar to a 4-pin relay, with an added step for pin 87a.

1. Perform steps 1-3 from the 4-pin test. Ensure the coil clicks when power is applied.
2. Test Normally Closed (NC) Continuity: With NO power applied to the coil, test continuity between pins 30 and 87a. You should get a low resistance reading (near 0 ohms).
3. Test Normally Open (NO) Continuity (Coil Energized): While power is applied to the coil (and it’s clicking), test continuity between pins 30 and 87. You should get a low resistance reading.
4. Verify NC Open (Coil Energized): Simultaneously, with power applied to the coil, test continuity between pins 30 and 87a. You should now get an open circuit (infinite resistance).

If any of these tests fail, your relay is likely bad and needs replacement.

Common Relay Pin Functions

Pin Number	Function	Description
85	Coil Ground	Receives ground signal to activate coil.
86	Coil Power	Receives 12V power to activate coil.
30	Common Input	Constant 12V power supply for the switch.
87	Normally Open Output	Power flows here when relay is energized.
87a	Normally Closed Output	Power flows here when relay is NOT energized (5-pin only).

Diagnosing Relay Issues: Beyond the Test

Sometimes, a component doesn’t work, but it’s not always the relay. Electrical systems can be tricky.

A bad fuse, wiring issue, or even the component itself could be the culprit.

Common Symptoms of a Failing Relay:

• Intermittent Operation: The component works sometimes, but not always.
• No Operation: The component doesn’t work at all.
• Clicking but No Action: You hear the relay click, but the component doesn’t turn on. This often means the coil is fine, but the internal contacts are burnt or stuck.
• Constant Operation: The component stays on, even when it should be off. This indicates the relay contacts are stuck closed.

Troubleshooting Steps:

1. Check the Fuse: Always start with the fuse. A blown fuse will prevent power from reaching the relay or the component it controls.
2. Visual Inspection: Look for obvious signs of damage or corrosion on the relay and its socket.
3. Swap with a Known Good Relay: If you have an identical relay from a non-critical circuit (like the horn, if you don’t need it temporarily), swap it. If the problem moves or is resolved, you’ve found your faulty relay.
4. Check Wiring: Ensure all wires connected to the relay and the component are secure and free of damage.

Understanding your car’s wiring diagram can be a huge help here. It shows you the entire circuit path.

Common Symptoms of a Failing Relay

Symptom	Potential Cause	Next Step
Component not turning on	Open circuit, bad coil, stuck contacts	Test relay, check fuse, inspect wiring
Component staying on	Stuck closed contacts	Test relay, replace if contacts are fused
Intermittent operation	Loose connection, worn contacts	Inspect connections, test relay thoroughly

Sourcing a New Relay and Best Practices

Once you confirm a relay is bad, replacing it is usually simple. Relays are widely available and generally inexpensive.

You can find new relays at AutoZone, NAPA, O’Reilly Auto Parts, or your car’s dealership.

Matching the Right Relay:

It’s crucial to replace a faulty relay with one that matches its specifications. Look for these details:

• Voltage: Most automotive relays are 12V.
• Amperage Rating: This indicates the maximum current the relay can safely handle. Never use a relay with a lower amperage rating.
• Pin Configuration: Ensure it has the correct number and arrangement of pins (e.g., 4-pin NO, 5-pin NO/NC).
• Form Factor: While not always critical, matching the physical size helps ensure it fits properly in the fuse box or relay block.

Consider buying an OEM (Original Equipment Manufacturer) relay for critical systems like the fuel pump or engine control. Aftermarket options are often reliable for less critical functions.

Always disconnect your car’s battery before replacing any electrical components. This prevents accidental shorts or damage to your vehicle’s sensitive electronics.

Keeping spare common relays in your glove box can be a smart move. They are small and can get you out of a bind on the road.

Can AutoZone Test Relays? — FAQs

Can I test a relay without a multimeter?

While a multimeter is best for precise checks, you can do a basic “click test” with a 9V battery and jumper wires. Connect the battery to the coil pins (85 and 86) and listen for a click. This confirms the coil works, but doesn’t verify the switch contacts are closing properly.

Are all automotive relays interchangeable?

No, relays are not universally interchangeable. They vary by voltage, amperage rating, and pin configuration (4-pin normally open, 5-pin normally open/closed). Always replace a relay with one that has identical specifications to ensure proper function and prevent electrical issues.

What are common signs of a bad relay?

Common signs include a component not working at all (e.g., headlights out, horn silent), intermittent operation, or the component staying on constantly. You might also hear a rapid clicking sound from the relay without the component activating. These symptoms suggest the relay’s internal contacts or coil may be faulty.

Where are relays typically located in a car?

Relays are usually found in the fuse box under the hood, often near the battery or fender. Some vehicles also have a secondary fuse/relay box inside the cabin, usually under the dashboard or in the glove compartment. Consult your vehicle’s owner’s manual for exact locations.

Is it safe to swap relays for testing purposes?

Yes, it’s generally safe to swap a relay from a non-critical circuit (like the horn or defroster) with one from a suspected faulty circuit for a quick test. Ensure the relays are identical in type and rating before swapping. Always return the original relay to its proper location after testing.