Have you ever noticed your car’s lights, fans, or other components acting up? Well, it could be due to a faulty relay. Signs of relay failure might include lights not turning on or systems not responding. But don’t worry; there’s a simple way to figure out if a relay is the culprit.
So, if you’re curious to find out if a relay is causing the problem, keep reading:
What is the function of relays in cars?
In cars, a relay is an electrical device that plays a crucial role in controlling various electrical components and systems. It acts as a switch that is operated electronically, allowing a low-power signal to control a higher-power circuit.
Relays are commonly used in automotive systems to control components that require significant power, such as the starter motor, headlights, cooling fans, fuel pumps, and more. The main function of a relay in cars is to provide a safe and efficient way to control these high-power devices using lower-power signals.
Why does Relay fail?
- Relays in cars fail due to factors including wear and tear, high current loads, electrical arcing, vibration, and environmental conditions.
- The moving parts in relays, particularly the contacts responsible for opening and closing circuits, can wear out, rust, or pit over time, leading to unreliable operation.
- High-current devices like starter motors and headlights stress relay contacts, causing degradation, overheating, and eventual failure.
- Electrical arcing during contact closure damages the relay contacts. At the same time, vibrations and shocks from driving can loosen internal components, resulting in intermittent operation or failure.
- Environmental factors such as moisture, dirt, and temperature fluctuations can corrode relay contacts, affecting conductivity.
- Overheating due to engine heat or poor ventilation accelerates internal component breakdown.
Age, mileage, electromagnetic interference, incorrect voltage or current, and manufacturing defects also contribute to failures. - Choosing quality relays, regular maintenance, and timely replacement can help mitigate the risk of relay failure in cars.
Signs of Relay failure:
Signs of relay failure can include:
- Erratic operation of electrical components.
- Intermittent starting issues in the vehicle.
- Unresponsive systems like headlights or cooling fans.
- Audible clicking noises from the Relay itself.
In how many ways we can test a Relay?
There are several ways to test a car relay to determine its functionality and identify potential issues. Here are the primary methods:
- Visual Inspection:
Inspect the Relay for physical damage, burnt spots, or melted plastic. Check for corrosion on the pins and terminals.
- Test Light Method:
Use a test light to check for power at the control and load pins while the vehicle’s key is in the “ON” position.
Activate the control circuit to ensure the Relay engages and the load circuit receives power.
- Multimeter Method:
Measure the resistance of the relay coil with a multimeter (usually pins 85 and 86). Check for continuity in the load circuit (pins 30 and 87) with the Relay activated.
- Bypass Test:
Temporarily bypass the Relay by connecting pins 30 and 87 using a jumper wire. Check if the load operates; this helps determine if the issue lies with the Relay or the load itself.
- Listen for Click:
Activate the control circuit and listen for a clicking sound from the Relay. This indicates that the Relay is engaging.
- Voltage Drop Test:
Test the voltage drop across the relay contacts while it’s engaged. A significant voltage drop could indicate a worn-out relay.
Identify a bad Relay with visual inspection?
Locate the relay:
Relays in a car are typically located in the fuse box under the hood, near the battery, or inside the car, often beneath the dashboard or in the trunk. The exact location can vary based on the car’s make and model.
Examine the Exterior:
Inspect the Relay’s casing for any physical damage, cracks, or signs of overheating (discoloration or melting).
Check the Relay’s wiring connections for any signs of fraying, corrosion, or loose connections.
Check the Contacts:
Gently remove the relay cover (if applicable) to access the internal components.
Inspect the Relay’s contacts (small metal pieces that close or open the circuit) for signs of corrosion, pitting, or burning. Healthy contacts should be clean and smooth.
Inspect the Coil and Armature:
If visible, examine the coil and armature of the Relay. The coil is usually a winding of wire, and the armature is the moving part that bridges the contacts.
Ensure the coil wires are intact and not damaged.
Check the armature for any signs of wear, such as uneven contact surfaces or visible damage.
Look for Loose Components:
Check if any internal components or wires have come loose due to vibration or damage.
Listen for Clicking:
Sometimes, a faulty relay may emit a rapid clicking sound when the vehicle is turned on or when the Relay should be engaged.
Odor:
If there’s a burnt or unusual odor coming from the Relay, it could indicate overheating or damage.
What is a Test Light & how to use it?
A test light, also known as a test lamp or voltage tester, is a simple handheld tool used to determine the presence of electrical voltage in a circuit or electrical component. Mechanics, electricians, and DIY enthusiasts often use it to troubleshoot electrical issues, check for power in a circuit, and verify if a particular electrical component is receiving power.
If you’re troubleshooting an electrical issue, you can use the test light to trace the circuit’s path and identify where the voltage is lost. This can help you pinpoint the exact location of the problem.
How to use a test light:
Materials Needed:
- Test light
- Safety gloves
- Circuit or component you want to test
- Safety Precautions:
Before working with electrical components, wear appropriate safety gear, including safety goggles, to protect your eyes in case of any accidents.
Ensure the power source to the circuit or component you’re testing is turned off to prevent electric shock.
- Inspect the Test Light:
Examine the test light for any wire, insulation, or probe damage.
Ensure that the test light is in proper working condition.
- Identify the Circuit or Component:
Determine which circuit or component you want to test. This could be a fuse, switch, light socket, or any other part of an electrical system.
- Prepare the test light:
Connect the clip or clamp on the test light’s wire to a good ground source. This can be a metal part of the vehicle or the battery’s negative terminal. The ground connection ensures that you have a reference point for voltage measurement.
- Touch the probe to the tested circuit:
With the ground connection secured, use the test light’s probe (the pointed end) to touch different points within the circuit or component you’re testing.
If the circuit is live and has voltage, the test light will illuminate, indicating the presence of voltage.
- Check the results:
If the test light illuminates, it means there is voltage in the circuit or component you’re testing.
If the test light doesn’t illuminate, it suggests no voltage or power in the tested area. This could indicate a faulty component, a broken circuit, or a power interruption.
Perform Additional Tests:
- Disconnect the Test Light:
After you’re done testing, disconnect the test light from the ground source and the circuit/component you tested.
Here is he complete guide to test Relays with test light.
How to test Relay with test light?
- To test a relay using a test light, follow these steps: First, ensure the test light works by connecting its clip to a ground source and checking if it illuminates when the probe touches the battery’s positive terminal.
- Identify relay pins labeled 85, 86, 30, and 87. Probe pin 86 with the test light while the ignition is on, confirming power.
- Touch pin 85, activate a control signal, and check for illumination. Confirm power input by touching pin 30 with the engine running.
- Test pin 87 while the control signal is active to verify power reaching the load. Deactivate the signal and touch pin 87 again to ensure power is cut.
- After testing, turn off the ignition and disconnect the battery. This method helps diagnose relay functionality and potential electrical issues.
Step 1: First, test the fuses & replace it if any of them is bad.
Here are the tips about testing fuses using a test light:
If something in your vehicle, like a light or radio, isn’t working, it could be due to a blown fuse. The first step is to locate the fuse box.
1: Locating the Fuse Box
Most vehicles have an under-hood fuse box covered by a lid. The lid usually contains a key indicating which fuse corresponds to which function.
The location of the fuse box in a car varies based on the vehicle’s make and model. Common locations include under the hood near the battery, under the dashboard near the steering column, in the trunk or cargo area, and occasionally on the passenger side.
The fuse box houses a fuse that controls functions like lights, radios, and engine-related systems. Consulting the owner’s manual or seeking professional assistance can help identify the specific location in your car.
2: Identifying Blown Fuses Visually:
To identify a blown fuse in a car through visual inspection, look for a break or gap in the metal strip inside the fuse. Blown fuses can be visually identified by a broken U-shape inside the fuse.
If the metal strip is intact, the fuse is likely functional; if it’s broken or damaged, the fuse is blown.
In some cases, the damage might be difficult to see, making testing the fuse using other methods essential.
3: Testing Fuses with a Test Light
A test light can be used to check fuses quickly and easily. Before using the test light on fuses, test it to ensure it’s functional by connecting it to the negative battery terminal and touching the metal probe to the positive terminal. If the test light illuminates, it’s working fine.
To test a fuse with a test light, touch the test light’s probe to both sides of the fuse’s pins.
If the light illuminates on both sides, the fuse is good and passes current through it.
4: Identifying Blown Fuses
If one side of the fuse lights up the test light while the other doesn’t, it indicates a blown fuse. The side that doesn’t light up corresponds to the broken connection within the fuse.
If neither side of the fuse lights up the test light, there’s no power going to the fuse. This doesn’t necessarily indicate a blown fuse but might suggest that the associated function is off or requires a specific condition (like the key being on) to receive power.
Step 2: Relay Testing Basics:
Testing relays in automotive is typically done in the car, not on a bench with a battery source. You can perform most relay tests at the relay base using a test light or voltmeter.
Using a test light with low amperage prevents damaging sensitive circuits like computer control circuits.
Tools for Relay Testing:
Use a test light or a multimeter as they doesn’t draw too much amperage, as high amperage might damage PCM (Powertrain Control Module) You will also need jumper wires.
Step 3: Locate the Relay box:
The relay box’s location varies in vehicles, commonly found under the hood near the battery or beneath the dashboard. Other possible spots include the trunk, near the fuse box, inside the cabin, and even in the wheel well of trucks and SUVs.
To pinpoint the exact position, consult the vehicle’s manual or search online for your car’s make and model.
Step 4: Ways to identify Relay pins:
Here’s a general process to identify relay pins:
- Examine the relay:
Look for the Relay’s physical shape and its number of pins. Common automotive relays have either 4 or 5 pins.
- Read the labeling:
Many relays have labels on the casing indicating the function of each pin. These labels might be abbreviated (e.g., “30,” “87a,” “85,” “86”) or use symbols.
- Determine pin arrangement:
Observe the orientation of the pins. In most cases, pins 85 and 86 (control pins) are diagonal, and pins 30 and 87 (load pins) are diagonal.
- Refer to diagrams:
Vehicle manuals, service guides, or online resources might provide relay diagrams for your car’s make and model. These diagrams illustrate pin functions.
- Bypass the relay:
If pins aren’t labeled, or diagrams are unavailable, you can use trial and error to determine pins. This is done by gently connecting pins 30 and 87 to see if the load (controlled device) activates.
Last Step: Test the relay circuit with test light:
Use a test light connected to the battery negative and check on the battery positive to verify a good ground.
Step 1: Test the Control Circuit
Touch the probe of the test light to pin 86, which is usually the control circuit’s power source (usually comes from a switch, sensor, or computer). The test should be done while the engine is running or the ignition is turned on. The test light should illuminate, indicating the presence of power.
Step 2: Test the Load Circuit
Touch the probe of the test light to pin 85 while keeping the clip on the vehicle’s ground. The engine should be running, the ignition should be turned on, and the specific control action should be applied (e.g., turning on headlights). If the test light illuminates, the control circuit is working correctly.
Step 3: Test the Load Side
Touch the probe of the test light to pin 30 while the engine is running, or the ignition is turned on. It is usually the input of the load circuit. It should be connected to a power source (e.g., the battery). The test light should illuminate.
Step 4: Test Pin 87
Touch the probe of the test light to pin 87, the output of the load circuit. The engine should be running, and the specific control action should be applied (e.g., turning on headlights).
If the Relay is functioning, the test light should illuminate.
How to bypass a relay?
First, to temporarily bypass a relay for diagnostic purposes, identify the Relay’s load (controlled) and control pins, ensuring the ignition is turned off, and the vehicle’s battery is disconnected.
Using a suitable jumper wire, connect one end to the load pin (pin 30), the input power side, and the other end to the control pin (pin 85 or 86), completing the circuit.
Reconnect the battery, activate the control signal (e.g., turn on the ignition), and check if the load (controlled component) functions correctly.
After testing:
- Turn off the ignition.
- Disconnect the battery again.
- Remember that bypassing should only be a temporary step for diagnosis, not a permanent solution.
How to test a relay with a multimeter?
Testing a relay using a multimeter is a useful diagnostic method to determine its functionality. Here’s how to do it:
Step 1: Set up your multimeter
Ensure your multimeter is set to measure resistance (ohms) and/or continuity.
Step 2: Identify relay pins
Familiarize yourself with the Relay’s pinout. Common pins include 85 (control), 86 (control), 30 (power supply), and 87 (load).
Step 3: Measure coil resistance (85 and 86)
Place the multimeter’s probes on pins 85 and 86 (control pins).
A functional relay usually displays a resistance reading between 50 to 120 ohms. No reading or an extremely high reading indicates a faulty coil.
Step 4: Test continuity in Pin 30 and 87
- Set the multimeter to the continuity or resistance mode.
- Connect one probe to pin 30 (power supply) and the other to pin 87 (load).
- Activate the Relay (apply voltage to the coil, usually pins 85 and 86).
- The multimeter should display continuity or a low resistance reading, indicating that the relay contacts function correctly.
Step 5: Check contacts in Normally Closed position
If the Relay has a normally closed (NC) contact (labeled as 87a), perform the same continuity test between pins 30 and 87a.
There should be no continuity when the Relay is not activated and continuity when the relay coil is energized.
Step 6: Confirm load circuit (87 and 30)
Test continuity between pins 87 and 30 with the relay coil deactivated. To select the continuity setting, rotate the multimeter dial to ⇥(continuity/diode sign).
There should be no continuity when the coil is not energized.
Step 7: Activate load circuit (87 and 30)
Energize the relay coil and test continuity between pins 87 and 30 again.
Continuity should now be present, confirming that the Relay allows current flow.
Step 8: Check control signal (85 and 86)
Set the multimeter to DC voltage. DC voltage sign is DCV or V⎓.
Connect the probes to pins 85 and 86, with positive and negative polarity matching the Relay’s control voltage source.
Apply the control signal (e.g., turn on the key) and ensure the multimeter displays the appropriate voltage (usually 12V).
Frequently Asked Questions
- How to test a relay without a multimeter?
You can test a relay without a multimeter by using a test light. Connect the test light’s clip to a known ground source and touch the probe to the Relay’s control and load pins while the key is turned on or the engine is running. If the test light illuminates both pins, the Relay will likely function correctly.
- How to test a relay with a 12v battery?
To test a relay using a 12V battery, first, identify the Relay’s control pins (usually 85 and 86) and load pins (usually 30 and 87).
Connect a jumper wire from the positive terminal of the 12V battery to the control pins, energizing the relay coil.
Using a test light or multimeter in continuity mode, touch one probe to the battery’s positive terminal and the other to the load pins. If the Relay is functional, you’ll hear a click and observe the test light illuminating or the multimeter showing continuity.
Disconnect the jumper wire to deactivate the Relay and retest the load pins for continuity; there should be no continuity. This simple test with a 12V battery can help determine the Relay’s proper operation.
- What is the difference between 4 pin & 5 pin relays?
The difference between 4-pin and 5-pin relays is in their functionality and purposes. Both relay types serve as switches for controlling electrical components, with 4-pin relays suited for straightforward control and 5-pin relays offering added flexibility.
A 4-pin relay includes two coils and two contact pins, ideal for fundamental on/off tasks. In contrast, 5-pin relays have an extra pin, often labeled 87a, providing both normally open and normally closed contacts.
This versatility accommodates maintaining a specific state without a control signal, which is helpful for applications like headlights’ high and low beams.
Conclusion
In conclusion, testing relays is essential when troubleshooting car electrical issues. When you notice signs like lights not working or unresponsive systems, a faulty relay might be the cause. You can employ various methods to test relays, such as visual inspection, a test light, or a multimeter.
A test light is a straightforward tool that helps identify voltage presence in circuits. By following simple steps like connecting the test light to good ground and touching its probe to different points within a circuit, you can confirm the existence of voltage.
Relays, crucial in controlling high-power components, can fail due to various factors. Signs of failure encompass erratic system behavior, intermittent starting problems, and clicking sounds. Performing tests on relays through methods like the test light or multimeter can help identify issues and ensure efficient vehicle operation.
Remember to prioritize safety and consult professional assistance when needed.
If you still need any assistance, ask us in the comments below.