A warning light related to your car’s emissions system just appeared on your dashboard. You are not sure whether this is the same as the Check Engine light, whether it is serious, or whether you can still drive. This guide answers all of those questions clearly and tells you exactly what to do next.
What Does the Emission Control System Light Look Like
The emission control system light varies by car manufacturer. On many vehicles, it appears as the same engine outline symbol as the check engine light, shown in yellow or amber. On others it may show the letters EPC, which stands for electronic power control, or display the word EMISSION.
On some European car models, particularly Volkswagen, Audi, Skoda, and SEAT, the EPC light is a separate symbol from the check engine light and specifically relates to the electronic throttle and emissions systems. On most other cars, an emissions fault is reported through the standard check engine light with a specific fault code stored in the system.
If you are unsure which light is on, a diagnostic scanner will tell you the exact fault code and confirm whether it is an emissions-related fault.
What Is the Emission Control System
Your car produces exhaust gases when it burns fuel. The emission control system is a collection of components that work together to reduce how much of those gases escape into the atmosphere. These components include the catalytic converter, oxygen sensors, exhaust gas recirculation valve, evaporative emission control system, and, on diesel cars, the diesel particulate filter.
When the emission control system light comes on, it means one or more of these components is not working correctly, and the car is producing more emissions than it should. It does not always mean there is a serious mechanical fault, but it does mean the car needs attention.
How Is This Different From the Check Engine Light
This is the question most drivers ask first. The honest answer is that on many cars they are the same light. The check engine light covers a wide range of faults, including emission control faults. When a diagnostic scanner reads the fault code, it will tell you whether the fault is emissions-related or something else.
On some cars, particularly European models, there are separate warning lights for engine management faults and emission system faults. In those cases, the emission light being on without the Check Engine light suggests the fault is specifically in the emissions components rather than the core engine.
In either case, the correct first step is the same. Get the fault code read by a scanner to find out exactly what has triggered the light.
Common Causes of the Emission Control System Light
Faulty Oxygen Sensor: Oxygen sensors measure the amount of oxygen in the exhaust gases before and after the catalytic converter. They help the engine control unit fine-tune the fuel mixture for clean combustion. A failed oxygen sensor is one of the most common reasons for an emissions warning light. The car will still run, but fuel economy and emissions will be affected.
Failing Catalytic Converter: The catalytic converter converts harmful exhaust gases into less harmful ones before they leave the exhaust pipe. When it starts to fail, it can no longer process emissions efficiently, and the oxygen sensors detect abnormal readings. A failing catalytic converter can cause the car to run rough and reduce performance noticeably.
Loose or Damaged Fuel Cap: This is one of the simplest and most overlooked causes. The fuel cap seals the fuel tank and prevents fuel vapours from escaping into the atmosphere. If the cap is loose, cracked, or missing, the evaporative emission control system detects a leak and triggers the warning light. Always check the fuel cap first when this light appears. Tighten it firmly and check if the light clears after a few driving cycles.
Faulty EGR Valve: The exhaust gas recirculation valve, commonly called the EGR valve, recirculates a small amount of exhaust gas back into the engine to reduce nitrogen oxide emissions. When it gets clogged with carbon deposits or fails, it affects the combustion process and triggers the emissions warning. A stuck open EGR valve can cause rough idling and a stuck closed valve can increase emissions significantly.
Evaporative Emission Control System Leak: The evaporative emission control system, often called EVAP, captures fuel vapours from the fuel tank and prevents them from escaping into the air. A leak anywhere in this system, from a cracked hose to a faulty purge valve, will trigger the emissions warning light. EVAP faults are often caused by nothing more serious than a loose fuel cap.
Diesel Particulate Filter Blockage: On diesel cars, the diesel particulate filter traps soot particles from the exhaust. Over time, it needs to regenerate, which means burning off the trapped soot at high temperature during longer drives. If the car is used mainly for short journeys, the filter never gets hot enough to regenerate, and it becomes blocked. A blocked DPF triggers the emission warning light and can cause significant performance loss.
Spark Plug or Ignition Fault: Misfiring spark plugs cause unburned fuel to pass through the engine into the exhaust. This damages the catalytic converter over time and immediately increases emissions. An ignition fault that causes misfires will often trigger both the Check Engine light and an emissions-related fault code.
How Serious Is This Light
The answer depends on the cause. A loose fuel cap is not serious at all and costs nothing to fix. A failing catalytic converter is a more expensive repair. A misfiring engine that is sending unburned fuel into the exhaust is actively damaging the catalytic converter while you drive, which makes it more urgent.
As a general rule, if the car feels and drives normally and the only issue is the warning light, you can drive to a garage to get it checked without causing immediate damage. If the car is running rough, misfiring, smelling strongly of fuel, or showing a loss of power alongside the warning light, treat it with more urgency.
What To Do When This Light Comes On
Step 1: Check the fuel cap first. Remove it, inspect it for cracks, and refit it firmly until you hear it click. This takes 30 seconds and fixes the problem in a surprising number of cases.
Step 2: Drive normally for two to three cycles, meaning starting and driving the car a few times, to see if the light clears on its own after the fuel cap is tightened.
Step 3: If the light stays on, get the fault code read with a diagnostic scanner. Most garages and many auto parts shops will do this quickly.
Step 4: Note the exact fault code and use it to understand which component is involved before agreeing to any repair work.
Step 5: If the car is running rough or misfiring alongside the emissions light, do not delay. Continued misfiring actively damages the catalytic converter, which is expensive to replace.
Step 6: For diesel cars with a blocked DPF, take the car for a longer drive at motorway speed to allow the filter to regenerate before booking a service.
Can You Drive With the Emission Control System Light On
In most cases, yes, as long as the car is driving normally. An emissions fault that is just a sensor, a loose fuel cap, or an EVAP leak will not cause the car to break down or damage the engine in the short term.
However, do not ignore this light for weeks or months. Some emissions faults, particularly a misfiring engine or a failing catalytic converter, get progressively worse and more expensive the longer they are left. Get it scanned and diagnosed as soon as reasonably possible.
Emission Control Light After Filling Up With Fuel
If this light came on shortly after filling the fuel tank, a loose or improperly fitted fuel cap is almost certainly the cause. Remove the cap, check it for damage, and refit it firmly. The light may take a day or two of normal driving to clear on its own once the cap is properly sealed.
Quick Summary
What | Detail |
Light Color | Yellow or Amber |
Symbol | Engine outline or EPC letters depending on car brand |
Severity | Low to Moderate depending on cause |
First Check | Fuel cap: tighten firmly and check if the light clears |
Most Common Cause | Loose fuel cap, faulty oxygen sensor, EGR valve fault |
Risk if Ignored | Catalytic converter damage, failed emissions test, worsening fault |
Related Warning Lights
These warning lights are closely connected to engine performance and the emissions system:
- Throttle Control Warning Light – Electronic throttle system fault
- Mass Airflow Sensor Warning – Air intake fault affecting fuel mixture and emissions
- Engine Temperature Warning Light – Engine overheating requiring immediate action
- Oil Pressure Warning Light – Critical engine lubrication fault
This page is part of our complete guide to car dashboard symbols and meanings. To see every warning light explained in one place, visit our Car Dashboard Symbols