Can I still drive my car with a bad spark plug?
In most cases, you should not rely on a car with a known bad spark plug for normal driving. You may be able to complete a very short, careful trip to a repair shop, but driving longer distances or under heavy load increases the risk of engine damage and costly repairs.
Symptoms and what a bad spark plug does
If you're unsure whether a plug is failing, these warning signs can help identify a problem before it gets worse.
- Engine misfires or runs roughly, especially at idle or during acceleration
- Noticeable loss of power or sluggish acceleration
- Decreased fuel economy and more frequent trips to the gas station
- Difficulty starting the engine or frequent stalling
- Check Engine Light or misfire codes (for example P030x codes where x is the cylinder number)
- Unburned fuel smells like gasoline from the exhaust
- Rough idling, vibrations, or engine shake
- Visible fouling on the spark plug tip or worn/damaged ignition coil boot
If you notice one or more of these signs, you should plan to have the ignition system inspected and the plugs tested or replaced as needed.
What happens if you drive with a bad spark plug
Driving with a compromised spark plug can create cascading issues beyond the plug itself. Here are the main risks you should know about.
- Increased engine misfires which raise exhaust temperature and wear on the catalytic converter
- Unburned fuel entering the exhaust system, potentially damaging sensors and the exhaust manifold
- Additional stress on ignition coils and wiring, accelerating component wear
- Lower engine efficiency and higher emissions, which can trigger a failed emissions test
- Possible engine overheating or knock if the misfire is severe under load
These consequences can lead to expensive repairs, so addressing a suspected bad spark plug promptly is wise.
What to do if you suspect a bad spark plug
If you think a spark plug is failing, follow these practical steps to verify the issue and minimize risk while you arrange proper service.
- Check for diagnostic codes with an OBD-II scanner or at a shop—misfires are often identified by specific codes.
- Consult your owner’s manual or a trusted mechanic for the correct plug type, gap, and torque specification for your engine.
- Inspect ignition components (spark plug boots/wires or coil packs) for cracks, oil contamination, or wear that could mimic spark plug failure.
- If a single cylinder shows a persistent misfire and the plug appears worn or fouled, consider replacing that plug and, if needed, the adjacent plugs to maintain even performance.
- After replacement, clear codes and monitor for reappearance of symptoms. If misfire persists, there may be a fuel injector, coil, or compression issue.
- If you must drive to a shop, do so slowly and avoid high RPM or heavy loads to reduce strain on the engine.
Prompt diagnosis and timely replacement reduce the likelihood of collateral damage and help keep your vehicle reliable.
Maintenance considerations: choosing and replacing spark plugs
Types of spark plugs and how long they last
Spark plugs come in copper, platinum, and iridium variants. Copper plugs are cheaper but wear faster; platinum and iridium plugs last longer and are common in modern engines. Replacement intervals vary widely—from roughly 30,000 miles for some copper plugs to 60,000–100,000 miles for many platinum or iridium plugs—depending on the vehicle and driving conditions. Always follow the vehicle manufacturer's recommended service interval.
Cost and labor considerations
DIY replacement can save labor costs, but it's important to use the correct torque specifications and gapping. A dealership or independent shop can replace multiple plugs quickly, especially on engines with coil-on-plug ignition. Expect parts and labor to vary by vehicle make/model and plug type, with higher-end iridium/platinum plugs typically costing more upfront but offering longer service life.
Summary
Can you drive with a bad spark plug? You might be able to limp to a shop if the problem is mild, but it is not recommended to drive long distances or under heavy load. A failing plug can cause misfires, reduced power, and higher emissions, and it can damage the catalytic converter and other ignition components if left unattended. If you notice symptoms, get a diagnostic and replace the worn plug promptly. Regular maintenance aligned with your car’s manual helps prevent these issues and keeps your vehicle running smoothly.
