Time to Replace the Spark Plugs

Several topics in our blog are related to spark plugs. We have mentioned their role at various stages of car functionality and the troubles they can cause. Even so, we are going to focus on the nuances of spark plug maintenance.

What are spark plugs and why do you need them?

Spark plugs are small but vital components of your engine’s ignition system. Their main job is to ignite the air-fuel mixture in the combustion chamber by creating a spark between their electrodes. This spark initiates the combustion process that powers the engine. Without properly working spark plugs, your car simply won’t run efficiently, or it might not start at all. They ensure quick engine start-up, smooth acceleration, optimal fuel consumption, and stable idling. Therefore, these small parts have a huge impact on overall engine performance.

What causes spark plugs to fail?

Several factors can lead to spark plug deterioration or failure. Frequent reasons include:

• Carbon deposits due to an overly rich air-fuel mixture or bad fuel quality.

• Oil fouling, when oil leaks into the combustion chamber and covers the spark plug tip.

• Overheating, often caused by improper heat range selection or cooling system issues.

• Electrode wear, which occurs naturally over time and reduces the spark’s effectiveness.

• Incorrect spark plug gap, whether from factory error or wear, leading to weak sparks or misfires.

• Mechanical damage, such as cracks in the ceramic insulator from improper installation.

All these factors shorten the lifespan of spark plugs and cause misfires, hard starts, or rough idling.

What does a bad spark plug look like?

Recognizing bad spark plug symptoms early helps avoid serious engine problems. Typical signs of a bad spark plug include rough idling, engine misfires, sluggish acceleration, engine surging, hesitation, poor fuel economy, and difficulty starting the car. Visual inspection can also give you answers to how to tell if a spark plug is bad. A healthy plug has a light tan or grayish deposit. However, a bad spark plug looks like one of these:

• Black, dry soot indicates carbon fouling.

• Wet, oily deposits suggest oil fouling.

• Blistered or melted electrodes show overheating.

• Heavy white deposits could mean coolant leaks.

If you notice any of these signs or appearances, it’s time to replace your spark plugs.

Can you drive with bad spark plugs? How do they affect engine performance?

Technically, you can still drive with worn or damaged spark plugs, but you really shouldn’t. Bad spark plugs cause incomplete combustion, reduced power, higher fuel consumption, and increased emissions. Extended driving with misfiring plugs can damage the catalytic converter and other expensive engine parts. Moreover, can a bad spark plug cause check engine light? Absolutely — a bad spark plug often triggers a misfire code, turning on your check engine light.

What trouble codes indicate spark plug problems?

When the “Check Engine” light comes on, it signals that the onboard computer has detected a problem. Misfire-related trouble codes such as P0300 to P0309, P0310 to P0314, and sometimes P0316 or P0363 may appear during diagnostics. However, keep in mind these codes don’t guarantee the spark plugs are the only issue — ignition coils, oxygen sensors, or catalytic converters might also be to blame. Always inspect the entire ignition system if misfire codes appear.

When should you replace spark plugs?

Spark plug replacement intervals depend on the type:

• Copper plugs: every 16,000–32,000 km (10,000–20,000 miles)

• Platinum plugs: every 96,000 km (60,000 miles)

• Iridium plugs: every 190,000 km (120,000 miles)

Always check your vehicle’s owner’s manual for manufacturer-specific recommendations. Also, replace spark plugs sooner if you notice signs of failure. Timely replacement ensures smooth engine operation and avoids costly repairs.

How to diagnose spark plug problems with inCarDoc

Early detection of spark plug issues saves you time and money. The InCarDoc app makes diagnostics easy: connect your smartphone to your car’s OBD-II port using a compatible adapter. Run a scan for trouble codes, monitor real-time engine data, and identify misfires or other ignition-related problems. InCarDoc provides you with detailed insights and helps you find the root cause of engine issues before they escalate.

A small detail is a big problem: change the spark plugs during

Spark plugs may seem like a minor detail in a complex car system, but their condition directly affects engine stability, fuel consumption, and driving safety. Worn or damaged spark plugs cause uneven idling, loss of power, increased emissions, and even failure of expensive components such as the catalyst. Do not wait for serious breakdowns or emergencies. Monitor the condition of the spark plugs, perform regular diagnostics, use the inCarDoc app to monitor and do not ignore bad spark plug symptoms in accordance with the manufacturer's recommendations. Remember: timely replacement of this small part will help to avoid big problems and save your money on repairs