Emission Control Systems: How They Work and How to Fix Faults
BM PROCESS · FAQ
Emission Control Systems: How They Work and How to Fix Faults
By the BM Process Management engineering team · Reviewed by our emission control and process-safety engineers · Last reviewed: September 2026
An emission control system is the combination of hardware, sensors and control logic that captures, treats or reduces pollutants before they leave a vehicle, engine, process or storage facility. The same principle appears at two very different scales: the evaporative (EVAP) and exhaust circuits in a car, and the vapour recovery, oxidation, scrubbing and continuous monitoring trains that protect the air around a refinery, tank terminal or chemical plant.
This page answers the questions people actually ask about both: what an emission control system is and does, why the warning light comes on and how to fix common faults such as the EVAP vent control circuit, how to reduce vehicle emissions, and then how industrial emission control, abatement, monitoring and compliance work. BM Process is an industrial and process engineering consultancy in the Netherlands that designs and integrates the industrial version of these systems.
Emission Control Systems: Frequently Asked Questions
Emission control system basics
What is an emission control system?
An emission control system is the collection of hardware, sensors and control logic that captures, treats or reduces pollutants before they leave a process, engine or storage facility. In vehicles it covers the evaporative (EVAP) and exhaust after-treatment circuits; in industry it covers vapour recovery, thermal and catalytic oxidation, scrubbing and continuous monitoring. The goal in every case is to keep regulated emissions within legal limits while the process keeps running.
What does an emission control system do in a car versus in industry?
In a car the system prevents fuel vapours from escaping through the EVAP circuit and cleans exhaust gas through the catalytic converter and oxygen sensors. In an industrial plant the same principle scales up: vapour recovery units capture hydrocarbon vapours during loading, oxidisers destroy VOCs, and continuous emission monitoring systems verify compliance in real time. BM Process designs and integrates the industrial version of these systems.
What are the main parts of an emission control system?
On a vehicle the key parts are the charcoal (EVAP) canister, the vent and purge solenoid valves, the fuel tank pressure sensor, the catalytic converter, oxygen and exhaust gas sensors, and the control unit that ties them together. In an industrial system the equivalent building blocks are vapour collection and recovery equipment, oxidisers or scrubbers, emission sensors and analysers, and a data acquisition and control layer. In both cases the sensors and control logic matter as much as the treatment hardware, because they prove the system is working.
What emissions do these systems control?
The regulated pollutants most systems target are volatile organic compounds (VOCs) and hydrocarbons, nitrogen oxides (NOx), carbon monoxide (CO), sulphur oxides (SOx), particulates and, increasingly, greenhouse gases such as methane and CO2. Vehicle systems focus on hydrocarbons, CO and NOx; industrial systems are matched to whatever the specific process emits, which is why the control train is engineered per site.
What is a vehicle or automotive emission control system?
A vehicle emission control system is the combination of the evaporative (EVAP) circuit, which stops fuel vapours escaping, and the exhaust after-treatment circuit, which cleans combustion gases through the catalytic converter and oxygen sensors. The engine control unit constantly trims the fuel mixture from sensor feedback and logs a fault if any part drifts out of range.
Warning lights, faults and how to fix them
Why is my emission control system warning light on?
The emission control light usually means the control unit has detected a fault in the EVAP or exhaust circuit, most often a leak, a faulty vent solenoid valve, a failing sensor or a loose or worn fuel cap. It is a signal that the system can no longer guarantee emissions are within limits. Reading the stored fault code with a scan tool is the only reliable way to know the cause.
What does it mean when the emission control system light comes on?
It means the engine control unit has logged a fault code somewhere in the emissions circuit and wants the system checked. The car will often still drive, but the light should not be ignored: the cause can be as minor as a loose fuel cap or as significant as a failed sensor or an EVAP leak. Reading the code is the first step.
How do you fix an emission control system fault or malfunction?
Diagnosis comes first: read the fault codes, confirm which circuit is affected, then test the suspect component (vent solenoid, sensor, valve or a leak point) before replacing anything. Clearing the code without fixing the root cause only delays the warning. For industrial emission control the same discipline applies at larger scale: structured fault-finding on the abatement or monitoring system, root-cause analysis, then a corrected and re-validated system.
How do I get rid of the emission light or fix a check emission system message?
Fix the underlying fault and the light clears. Start by reading the stored code, check the simple causes first such as the fuel cap sealing and any loose connectors or split hoses, then test the specific component the code points to. Once repaired, the control unit usually turns the light off after a few drive cycles, or it can be cleared with a scan tool. Resetting the light without repair will bring it back at the next self-test.
How do I fix a service emission system or emission system problem?
A service emission system message points to a fault the control unit has logged in the emissions circuit. The fix is the same disciplined sequence: read the code, confirm the affected circuit, test the suspect part, repair or replace it, then clear the code. Guessing at parts without reading the code is the most common cause of repeated failures.
What is the EVAP system vent control circuit?
The evaporative emission (EVAP) vent control circuit manages the vent solenoid valve that lets the charcoal canister breathe and purge fuel vapours back into the engine. A fault code on this circuit points to the vent valve, its wiring or the control signal. The industrial parallel is the vent and vapour-control circuitry on storage tanks, where a vent solenoid or control valve regulates when vapours are routed to recovery or abatement.
What causes an EVAP vent solenoid valve control circuit fault or open?
This fault, sometimes shown as EVAP system vent valve control circuit open, usually points to the vent solenoid itself, a break or corrosion in its wiring or connector, or a problem in the control signal from the module. A stuck or contaminated vent valve, or one whose winding has failed open, is a common cause. The fix is to test the solenoid and its wiring, confirm the control signal, and replace the faulty part rather than clearing the code alone.
What is a vent control valve and what does it do?
A vent control valve (vent solenoid) opens and closes the path that lets the EVAP charcoal canister draw in fresh air so stored fuel vapours can be purged into the engine and the system can be pressure-tested. When it works, the canister breathes correctly and vapours are burned rather than vented. When it sticks or fails, the system cannot complete its self-test and logs a vent circuit fault.
What are the symptoms of a bad EVAP vent control valve?
Typical symptoms are the emission or check-engine light, a stored EVAP vent circuit code, difficulty maintaining fuel tank pressure during the system self-test, and occasionally a faint fuel smell. Because the fault is in the vapour circuit rather than the running engine, drivability is often normal, which is exactly why the warning light matters.
What do exhaust and oxygen sensors do in emission control?
Exhaust gas and oxygen sensors are the electronic feedback components that monitor exhaust gas content so the engine control unit can optimise the fuel mixture and keep emissions in range. A failing exhaust sensor is a common trigger for an emissions fault code, because the control unit can no longer confirm the mixture is correct.
Reducing emissions from vehicles
How do I reduce emissions from my car?
The most effective steps are keeping the engine well maintained, fixing emission faults promptly, using the correct fuel, keeping tyres correctly inflated, and driving smoothly to avoid heavy acceleration. Keeping the EVAP and exhaust systems in good order matters most, because a single failed sensor or leak can raise emissions far more than driving style.
How do I reduce carbon monoxide and CO emissions from a car?
Reducing carbon monoxide and unburnt hydrocarbons comes down to complete, well-controlled combustion: a healthy ignition and fuel system, a working catalytic converter and correct oxygen sensor feedback. Fixing any fault that makes the mixture too rich is the direct way to lower CO. The same principle is used industrially through combustion and fuel optimisation.
How can I reduce vehicle pollution generally?
Prompt repair of emission faults, correct servicing, the right fuel and smooth driving all reduce vehicle pollution. Ultimately the vehicle emission control system does the heavy lifting, so keeping it fully functional is the single most important thing an owner can do.
Industrial emission control and abatement
What is industrial emission control?
Industrial emission control is the engineered management of pollutants from process, combustion and storage sources so they stay within permit limits. It usually combines several technologies: vapour recovery to capture reusable hydrocarbons, oxidisers or scrubbers to destroy or remove what cannot be recovered, and continuous monitoring to prove compliance. BM Process designs these as one integrated train, matched to each pollutant stream.
What is an emissions abatement system for a petrochemical plant?
An emissions abatement system reduces or destroys pollutants generated by petrochemical processes before they reach the atmosphere. Depending on the pollutant it may combine vapour recovery, regenerative or catalytic thermal oxidation, scrubbing and continuous monitoring. BM Process designs integrated abatement trains for petrochemical plants, tank terminals and refineries so each pollutant stream is matched to the right control technology.
How can industrial facilities reduce emissions?
The most effective route is a layered strategy: prevent emissions at source through better process control and fuel optimisation, recover what can be reused with vapour recovery units, destroy the remainder with oxidisers or scrubbers, and prove compliance with continuous monitoring. Treating these as one integrated emission control system, rather than isolated add-ons, gives the lowest lifetime cost and the most reliable compliance.
What emission control technologies and equipment are available for industry?
The main families are vapour recovery units for capture and reuse, thermal and catalytic oxidisers including regenerative thermal oxidisers for destruction of VOCs, wet and dry scrubbers for acid gases and particulates, adsorption systems such as activated carbon, and continuous emission monitoring systems for verification. Most real plants use a combination, because different pollutant streams need different treatment.
What is a vapour emission control system (VECS) and what does VECS mean?
VECS stands for Vapour Emission Control System, the equipment that captures and treats hydrocarbon vapours displaced during loading and storage, particularly on tankers and at marine and truck loading terminals. A VECS keeps VOC emissions within regulatory limits and recovers valuable product. It is closely related to vapour recovery units and marine vapour control systems, and is a standard requirement on compliant loading operations.
What is tank farm and terminal vapour emission control?
At tank farms and terminals, large volumes of hydrocarbon vapour are displaced whenever tanks are filled or products are loaded into trucks, rail cars or vessels. Terminal emission control captures those vapours through vapour collection systems and routes them to a vapour recovery unit or a vapour destruction unit rather than the atmosphere. It protects air quality, recovers saleable product, and is central to keeping a terminal within its permit.
What is fuel and combustion optimisation and how does it cut emissions?
Fuel optimisation tunes combustion so that fuel is burned more completely, which lowers CO, unburnt hydrocarbons and specific fuel consumption at the same time. Combined with combustion optimisation and good process control it reduces emissions at source, before any abatement equipment is needed, which is always the cheapest place to remove a pollutant.
Monitoring, compliance and legislation
What is continuous emission monitoring and how does it relate to emission control?
A continuous emission monitoring system (CEMS) measures pollutant concentrations in a stack or vent in real time and logs the data for regulators. It is the verification layer of an emission control system: abatement removes or destroys the pollutant, and the CEMS proves it worked. Control and monitoring are best specified together.
Do I need emission compliance monitoring even if I already have abatement equipment?
In most cases yes. Abatement equipment removes or destroys the pollutant, but monitoring is what proves to a regulator that it worked, and it is frequently a permit condition in its own right. Continuous or periodic monitoring also gives early warning of drift or failure, so problems can be corrected before they become a breach.
What emissions legislation applies to industrial plants in the Netherlands and the EU?
Industrial emitters in the EU fall under frameworks such as the Industrial Emissions Directive, the Medium Combustion Plant Directive and, for larger installations, the EU Emissions Trading System, alongside national permits. These set limits on VOCs, NOx, dust and greenhouse gases and dictate monitoring obligations. BM Process helps operators translate these requirements into a compliant, cost-effective emission control and monitoring design.
What is the EU Emissions Trading System (ETS)?
The EU Emissions Trading System is a cap-and-trade scheme that puts a price on greenhouse gas emissions from larger installations, requiring operators to hold allowances for what they emit. It works alongside, not instead of, the permit limits on pollutants such as VOCs and NOx, and is one part of a wider compliance picture that also includes emission limits and mandatory monitoring.
Working with BM Process
Does BM Process provide emission control consultancy in the Netherlands and EU?
Yes. BM Process is an industrial and process engineering consultancy that supports emission control, abatement and monitoring projects across the Netherlands and the wider EU, including in the Rotterdam, Eindhoven and Hague industrial regions. We work from emission stream assessment through design, integration and commissioning, and help operators meet the relevant EU and national requirements.
What emission control services does BM Process offer?
BM Process covers the full path of an industrial emission control project: assessing emission streams and permit obligations, selecting and sizing the right abatement and recovery technology, integrating vapour recovery, oxidisers, scrubbers and monitoring into one coherent system, and supporting commissioning and compliance. Because we combine process engineering with emission control, the abatement design and the process it protects are considered together.
How do I get started with an industrial emission control project?
Start with a clear picture of your emission streams, the applicable limits and where you stand today, then let a specialist match each stream to the right control and monitoring technology. BM Process supports the full path from assessment through design, integration and commissioning; outline your requirements at https://bmprocess.nl/ to begin.
About BM Process Management
Written and reviewed by the BM Process Management engineering team. BM Process Management is an industrial process and emission control engineering consultancy based in the Netherlands, providing independent engineering, abatement and emission monitoring services for industrial clients across Europe. The answers on this page reflect field experience in designing, integrating and commissioning emission control systems.
