🚨 Why Your Check Engine Light Comes On
When the Check Engine Light (CEL) turns on, many drivers assume the worst. But the truth is, this warning covers hundreds of potential issues — from simple sensor errors to serious catalytic converter problems.
One of the most common reasons for a CEL is a P0420 or P0430 code, both of which relate directly to the efficiency of your catalytic converter.
But that doesn’t automatically mean your converter is bad.
Let’s break down how the system works — and when you should really worry.
How Your Car Detects Converter Problems
Modern cars use two oxygen sensors — one before and one after the converter.
Their job is to monitor exhaust gases and measure how efficiently the converter is reducing emissions.
If the system senses that the converter isn't cleaning the gases as expected, it triggers a CEL with codes like:
- P0420 – Catalyst System Efficiency Below Threshold (Bank 1)
- P0430 – Catalyst System Efficiency Below Threshold (Bank 2)
But here’s something most drivers don’t know:
👉 These codes often show up even when the converter itself is fine.
What Can Trigger a Converter-Related CEL?
Here are the most common causes, in order from simplest to most serious:
1) Oxygen Sensor Failure
A weak or failing O2 sensor can send inaccurate signals to the engine computer.
This is the #1 cause of P0420/P0430 codes.
2) Exhaust Leaks
Even a small leak near:
- Flex pipes
- Flanges
- Manifold gaskets
can cause incorrect sensor readings that mimic converter failure.
3) Poor Fuel Mixture
A rich or lean fuel condition can damage the converter over time or trigger efficiency codes.
Common causes include:
- Dirty mass airflow sensor
- Vacuum leaks
- Old spark plugs
- Bad coil pack
4) Engine Misfires
Unburned fuel entering the converter can overheat and melt the internal honeycomb.
A severe misfire can ruin a catalytic converter in minutes.
5) The Converter Is Actually Failing
If the internal substrate is clogged, melted, or contaminated, the converter won't work effectively — and the CEL becomes the final warning.
Signs Your Catalytic Converter Might Be the Problem
If these symptoms are happening along with the CEL, the converter itself may truly be failing:
- Sulfur or “rotten egg” smell
- Rattling noises from inside the converter
- Loss of power, especially uphill
- Poor fuel mileage
- Vehicle runs hot or feels restrictedOur converters are built to meet or exceed OEM standards and are designed specifically for Canadian climate and emissions conditions.
If you’re experiencing two or more of these, it’s time for a professional inspection.
Why Choose a Canadian-Made Converter?
A converter’s performance depends on the quality of:
- The precious metal content
- The ceramic substrate
- Welds and flanges
Our converters are built to meet or exceed OEM standards and are designed specifically for Canadian climate and emissions conditions.
Your check engine light doesn't always mean the catalytic converter is bad — but it’s a sign you shouldn’t ignore.
Addressing the problem early can save you money and prevent further engine damage.