Steady or flashing
Steady: the engine computer has logged a fault that affects emissions or how the engine runs. The car is usually safe to drive for now. Book a diagnostic in the next week or so.
Flashing: the engine is misfiring badly. Unburned fuel is going into the exhaust, where it can overheat and destroy the catalytic converter, which is an expensive part. Slow down, avoid hard acceleration and get the car looked at today. If it is shaking or losing power, stop and call Tow Kings at (613) 276-4714.
Common causes
- A loose or worn gas cap. It really does happen. Tighten it until it clicks. The light will not go out right away, it takes a few drives.
- Oxygen sensors that have aged and slowed down.
- Spark plugs and ignition coils, the usual cause of a misfire.
- Vacuum leaks from cracked hoses and intake gaskets, very common on older cars.
- A dirty mass airflow sensor.
- The catalytic converter itself, often after years of an untreated misfire.
- Evaporative system leaks, the small hoses and valves that trap fuel vapour.
Why a free code read is not a diagnosis
A code like P0300 means random misfire. That could be spark plugs, a coil, a clogged injector, low fuel pressure, a vacuum leak or low compression. A free code read tells you P0300. It does not tell you which of those six things to fix.
A proper diagnostic means reading the code, looking at the live data and freeze frame, and then testing the suspect parts directly. That is how you avoid replacing three parts to fix one problem.
Can you just clear the code?
You can, and the light will go out. But the fault is still there, and the light will come back. Clearing codes also wipes the data that helps a technician find the problem, so it is better to leave it until the car is looked at.
What a diagnostic costs at King’s
Our diagnostic is $120 before tax, booked as a one hour appointment. We call you with the cause and a price for the fix before anything else is done. More about our diagnostics.
