Unlocking the Mystery of Glow Plug Voltage: How to Check It Easily

Your diesel engine’s glow plugs are crucial for starting in cold weather. They heat up the combustion chamber, allowing the fuel to ignite more easily. If your glow plugs aren‘t working properly, you might experience difficulty starting the engine, especially when it’s cold. Knowing how to check glow plug voltage is essential for diagnosing and resolving starting issues. This guide will walk you through the process step-by-step.

Understanding Glow Plugs

Glow plugs are small, electrically heated coils that are screwed into the cylinder head of a diesel engine. When you turn the ignition key, a current flows through the glow plugs, heating them to a high temperature. This heat preheats the combustion chamber, making it easier for the fuel to ignite when the engine starts.

Why Check Glow Plug Voltage?

Checking the voltage of your glow plugs is a crucial step in diagnosing starting problems in a diesel engine. Here are some reasons why you should check glow plug voltage:

• Faulty Glow Plug: A faulty glow plug might not be getting enough voltage, leading to insufficient heating and difficulty starting the engine.
• Faulty Relay: The glow plug relay controls the flow of electricity to the glow plugs. A faulty relay might not be supplying enough voltage to the glow plugs.
• Wiring Issues: Damaged or corroded wiring can also prevent the glow plugs from receiving the required voltage.

Tools You’ll Need

To check glow plug voltage, you’ll need the following tools:

• Digital Multimeter: A digital multimeter is essential for measuring voltage.
• Test Leads: You’ll need a set of test leads to connect the multimeter to the glow plugs.
• Socket Wrench: A socket wrench that fits the size of your glow plugs will be needed to remove them.
• Safety Glasses: Always wear safety glasses to protect your eyes from potential debris.

Checking Glow Plug Voltage: Step-by-Step Guide

1. Access the Glow Plugs: Locate the glow plugs on your engine. They are usually positioned on the cylinder head, near the injectors.

2. Disconnect the Glow Plug Wiring: Carefully disconnect the wiring harness connected to the glow plugs.

3. Set the Multimeter to Voltage Mode: Turn on your digital multimeter and set it to measure DC voltage.

4. Connect the Multimeter Leads: Connect the positive (red) lead of the multimeter to the positive terminal of the glow plug wiring harness. Connect the negative (black) lead to the negative terminal of the wiring harness.

5. Turn the Ignition Key to the “On” Position: Do not start the engine. Simply turn the key to the “On” position to activate the glow plug system.

6. Read the Voltage Reading: Observe the voltage reading on the multimeter. The voltage should be between 10-12 volts. If the voltage is significantly lower, it indicates a problem with the glow plug or the glow plug relay.

7. Repeat for Each Glow Plug: Repeat steps 4-6 for each glow plug to ensure they are all receiving the correct voltage.

Interpreting the Results

• Normal Voltage: If the voltage reading is within the expected range (10-12 volts), the glow plug is likely working correctly.
• Low Voltage: A low voltage reading indicates a problem with the glow plug, wiring, or the glow plug relay.
• No Voltage: If you don’t get any voltage reading, the glow plug is likely faulty, or there’s a problem with the wiring or the glow plug relay.

Troubleshooting Low Voltage Issues

If you encounter low voltage readings, you’ll need to troubleshoot the problem to determine the root cause. Here are some steps you can take:

• Inspect the Wiring: Check the wiring harness for any signs of damage, corrosion, or loose connections.
• Test the Glow Plug Relay: If the wiring looks good, test the glow plug relay to ensure it’s working properly.
• Replace the Glow Plug: If the glow plug is faulty, replace it with a new one.

Beyond Voltage: Other Glow Plug Checks

While checking voltage is crucial, it’s not the only test you can perform. Here are some additional checks:

• Resistance Test: Use your multimeter to measure the resistance of the glow plug. The resistance should be within the manufacturer’s specifications.
• Visual Inspection: Inspect the glow plug for any signs of damage, such as cracks or corrosion.

Replacing a Faulty Glow Plug

If you’ve identified a faulty glow plug, you’ll need to replace it. Here’s a general guide:

• Disconnect the Battery: Disconnect the negative battery terminal to prevent electrical shock.
• Remove the Glow Plug: Use the socket wrench to remove the faulty glow plug. Be careful not to damage the threads.
• Install the New Glow Plug: Install the new glow plug, making sure to tighten it to the correct torque specification.
• Reconnect the Battery: Reconnect the negative battery terminal.

Keeping Your Glow Plugs Healthy

Here are some tips for extending the life of your glow plugs:

• Use High-Quality Fuel: Use high-quality diesel fuel to prevent buildup of deposits in the glow plugs.
• Regular Maintenance: Have your glow plugs inspected and cleaned as part of your regular diesel engine maintenance schedule.
• Avoid Short Trips: Frequent short trips can cause condensation to build up in the engine, which can lead to glow plug problems.

Wrapping Up: Ensuring Smooth Starts

Knowing how to check glow plug voltage is essential for diagnosing and resolving starting problems in a diesel engine. By following the steps outlined in this guide, you can quickly identify faulty glow plugs and address the issue before it becomes a major problem. Remember to always prioritize safety and use the appropriate tools and techniques when working on your vehicle.

Answers to Your Most Common Questions

Q: What is the normal glow plug voltage?

A: The normal glow plug voltage is typically between 10-12 volts.

Q: How long should glow plugs stay on?

A: The duration of the glow plug cycle varies depending on the engine and temperature. It can range from a few seconds to several minutes.

Q: Can I drive my car with a faulty glow plug?

A: While you may be able to drive your car with a faulty glow plug, it’s not recommended. A faulty glow plug can lead to poor engine performance, increased fuel consumption, and difficulty starting, especially in cold weather.

Q: How often should I replace my glow plugs?

A: Glow plugs typically have a lifespan of 50,000 to 100,000 miles. However, it’s best to consult your owner’s manual for specific recommendations for your vehicle.

Q: Can I test glow plugs without removing them?

A: While it is possible to test glow plugs without removing them, it’s more difficult and less accurate. Removing the glow plugs provides a more reliable test and allows for a visual inspection.