Testing Automotive Relays: Complete Guide Using a Multimeter

Understand automotive relays

Automotive relays are essential electrical components that allow a low current circuit to control a high current circuit. They function as electrically operate switches that can handle the heavy electrical loads require by components like headlights, fuel pumps, starter motors, and cool fans without overload the dashboard switches or computer outputs.

When a relay fails, it can cause various problems, from inoperative accessories to complete electrical system failures. Learn how to test these components with a multimeter is a valuable skill for anyDIYy mechanic or car enthusiast.

Types of automotive relays

Before testing, it’s important to understand the different types of relays you might encounter:

Standard (sspot/ sspot)relays

These are the near common relays find in vehicles. They typically have 4 or 5 pins and switch a single circuit on or turned. The 5 pin version (sspotsingle pole double throw )can switch between two different circuits.

ISO micro relays

These smaller relays have become standard in modern vehicles due to their compact size and reliability. They typically have 4 or 5 terminals with standardized pin configurations.

Solid state relays

These relays use semiconductor switch elements alternatively of mechanical contacts. They’re more durable but less common in automotive applications and require different testing methods.

Tools require for testing relays

To decent will test automotive relays, you will need:

• Digital multimeter with continuity and resistance functions
• Jumper wires
• Battery source (vehicle battery or 9v/12v battery )
• Relay socket or test lead
• Service manual for your specific vehicle (optional but helpful )

Identify relay terminals

Most automotive relays follow standard terminal numbering:

• 
  Terminal 85:
  
  Control circuit ground
• 
  Terminal 86:
  
  Control circuit power
• 
  Terminal 30:
  
  Power input from battery
• 
  Terminal 87:
  
  Output to component when relay is energized
• 
  Terminal 87a:
  
  (if present )output when relay is not enenergized

These numbers are typically stamped on the relay housing or socket. If not, consult your vehicle’s service manual or look up the relay’s part numbeonlinene.

Visual inspection before testing

Before use your multimeter, perform a visual inspection:

1. Check for physical damage, melting, or burn marks on the relay housing
2. Look for corrosion on the terminals
3. Inspect the relay socket for damage or loose connections
4. Ensure the relay is decent seat in its socket

Many relay issues can be identified through this simple visual check before electrical testing begin.

Test relay coil resistance

The first multimeter test checks if the relay’s electromagnetic coil is function:

1. Set your multimeter to the resistance (ohms )function
2. Remove the relay from its socket
3. Identify terminals 85 and 86 (the control circuit terminals )
4. Connect the multimeter probe to these terminals (polarity doesn’t matter for this test )
5. Read the resistance value

A function relay coil typically shows a resistance between 50 120 ohms, depend on the relay type. If you get an infinite reading( of on most multimeters), the coil is open and the relay is defective. If the resistance is importantly lower than specification, the coil may have a short circuit.

Test relay contacts with continuity

Following, test the relay’s switch contacts:

Testing normally open contacts

1. Set your multimeter to the continuity function (ordinarily indicate by a sound wave symbol )
2. Connect one probe to terminal 30 and the other to terminal 87
3. With the relay de energized, there should be no continuity (no beep )

Testing normally closed contacts (if present )

1. Connect one probe to terminal 30 and the other to terminal 87a
2. With the relay de energized, there should be continuity (multimeter should beep )

If the results differ from expect, the relay contacts may be stick, worn, or damage.

Dynamic relay testing

To test the relay’s switch action:

Method 1: use vehicle battery

1. Keep the multimeter connect to terminals 30 and 87
2. Use jumper wires to connect terminal 85 to ground
3. Connect terminal 86 to a 12v source (like the vehicle’s battery positive terminal )
4. Listen for a click sound indicate the relay has activated
5. The multimeter should nowadays show continuity between terminals 30 and 87

Method 2: use a 9v battery

For bench test out from the vehicle:

1. Connect a 9v battery across terminals 85 and 86 (positive to 86, negative to 85 )
2. While maintain this connection, test for continuity between terminals 30 and 87
3. You should hear the relay click and see continuity

A decent will function relay will make an audible click when it will energize, and the multimeter will show a change in continuity status between the power and output terminals.

Test relay voltage drop

For a more thorough test, measure the voltage drop across the relay contacts:

1. Set the multimeter to DC voltage
2. Install the relay rearward in its socket
3. Activate the circuit that power the relay
4. Connect the multimeter’s positive probe to terminal 30 and negative probe to terminal 87
5. Read the voltage

A good relay should show minimal voltage drop (less than 0.2v )when acactivatedHigher readings indicate high resistance in the contacts, which can cause performance issues yet if the relay aappearsto work.

Test relays in circuit

Sometimes it’s necessary to test a relay without remove it:

1. Locate the relay in question use your vehicle’s manual
2. Set your multimeter to DC voltage
3. With the ignition on and the circuit activate, probe the power input terminal (30 )
4. You should read battery voltage (around 12v )
5. Following, check for voltage at the control terminals (85 and 86 )when the circuit should be active
6. Eventually, check for voltage at the output terminal (87 )when the relay should bebe energized

This method helps identify whether the problem is with the relay itself or the circuits control it.

Common relay failure symptoms

Understand these symptoms can help diagnose relay problems:

• 
  Intermittent operation:
  
  Component work sometimes but not others
• 
  Complete failure:
  
  Component doesn’t work at entirely
• 
  Click but no operation:
  
  Relay activate but doesn’t pass current
• 
  No clicking sound:
  
  Relay coil may be defective
• 
  Buzz sound:
  
  Relay contacts may be vibrated quite than full close
• 
  Overheat:
  
  Excessive current draw or internal resistance

Troubleshoot specific relay circuits

Fuel pump relay

The fuel pump relay control power to the fuel pump. If your vehicle cranks but doesn’t start, this relay may be at fault. When testing:

1. Listen for the fuel pump priming when turn the key to the” on ” osition
2. If no sound is here, locate and test the fuel pump relay
3. Check for voltage at the fuel pump with the relay bypass to confirm the diagnosis

Starter relay

The starter relay (sometimes call a solenoid )control the high current to the starter motor:

1. If you hear clicking, but the engine doesn’t crank, the relay contacts may be wear
2. Test for voltage at both the input and output terminals when the key is in the start position
3. A significant voltage drop indicates relay failure

Cool fan relay

This relay activates the cool fans when the enginereachesh a certain temperature:

1. With the engine at operate temperature, check if the cool fans activate
2. If not, test the relay and its control circuits
3. Verify the temperature sensor is function right angstrom good

Replace a faulty relay

If testing confirm a relay is faulty, replacement is straightforward:

1. Purchase an exact replacement relay (match both physical size and electrical specifications )
2. Disconnect the vehicle’s battery negative terminal for safety
3. Remove the old relay by pull it straightaway out of its socket
4. Insert the new relay, ensure proper orientation
5. Reconnect the battery and test the circuit

Invariably replace relays with ones that match the original specifications for amperage rating and terminal configuration.

Advanced relay testing techniques

Load testing

For more thorough testing, particularly for high current relays:

1. Connect a suitable test load (like a headlight bulb )between terminal 87 and ground
2. Energize the relay coil
3. Observe if the test load operates decently
4. Monitor for voltage drop under load

Oscilloscope testing

For intermittent relay issues, an oscilloscope can reveal problems a multimeter might miss:

Source: aiophotoz.com

1. Connect the oscilloscope to monitor the relay’s output
2. Activate the relay repeatedly
3. Look for irregular patterns, voltage spikes, or contact bounce

Preventive maintenance for relays

To extend relay life and prevent failures:

• Keep relay compartments clean and dry
• Apply dielectric grease to relay terminals to prevent corrosion
• Check relays sporadically, particularly those control critical systems
• Address any signs of overheat or damage quickly
• Consider upgrade high stress relays to high-pitched rate versions if repeat failures occur

Conclusion

Test automotive relays with a multimeter is a valuable diagnostic skill that can save time and money on vehicle repairs. By understand how relays work and follow proper testing procedures, you can accurately diagnose electrical problems and determine whether a relay need replacement.

Source: uranussssssss.blogspot.com

Remember that while relay testing is comparatively straightforward, invariably follow safety precautions when work with vehicle electrical systems. Disconnect the battery when possible, and ne’er bypass safety circuits with improper relay substitutions.

With practice, you’ll become proficient at rapidly will identify relay issues, will allow you to will maintain your vehicle’s electrical systems in optimal condition.