2018 Honda Accord Emissions System Problem

The 2018 Honda Accord emissions system problem is an issue that some owners have reported with the operation of the emissions control components in the 2018 model year Accord. Properly functioning emissions systems are crucial for engine performance, fuel economy, and reducing environmental pollution. This article will examine the causes, troubleshooting, and repair options for 2018 Honda Accord emissions system problems.

What Causes Emissions System Problems In The 2018 Honda Accord

There are several components in the 2018 Honda Accord emissions system that, if faulty, can cause issues:

Oxygen Sensors

The oxygen sensors monitor the oxygen levels in the exhaust stream. If they malfunction, it can cause emission problems.

Catalytic Converter

The catalytic converter reduces pollutants from the exhaust. If it becomes clogged or damaged, it affects emissions.

EGR Valve

The Exhaust Gas Recirculation (EGR) valve recirculates exhaust back into the engine. Failures lead to emission issues.

EVAP System

The Evaporative Emissions (EVAP) system prevents gas fumes from escaping the fuel system. Leaks can cause emission problems.

Symptoms Of Emissions System Problems

Some common symptoms that there may be an emission system problem honda accord 2018 include:

  • Illuminated check engine light
  • Reduced engine performance and acceleration
  • Increased exhaust fumes and odor
  • Higher fuel consumption and lower gas mileage
  • Engine surging or misfiring
  • Failed emissions testing

Diagnosing The Emissions Problem

Diagnosing the specific 2018 Honda Accord emissions system problem requires connecting an OBD-II scanner tool to read any diagnostic trouble codes (DTCs) stored in the engine computer.

Some common DTCs include:

  • P0420 – Catalytic Converter Efficiency Below Threshold
  • P0430 – Catalytic Converter System Efficiency Below Threshold Bank 2
  • P0135 – O2 Sensor Heater Circuit Malfunction
  • P0455 – EVAP System Leak Detected

The DTCs will point to the likely cause, whether it be a faulty oxygen sensor, bad catalytic converter, or leak in the EVAP system.

Repairing Emissions Problems In A 2018 Honda Accord

Once the root cause of the emissions system problem honda accord 2018 is diagnosed, repairs can be made:

Oxygen Sensor Replacement

Faulty O2 sensors need to be replaced. Plan for a repair cost of $200-300 for parts and labor.

Catalytic Converter Repair/Replacement

A clogged catalytic converter may be serviced, but complete replacement often becomes necessary. Expect to pay $1000-$2000 for a new Honda Accord catalytic converter from a muffler shop.

EGR Valve Cleaning/Replacement

Carbon buildup on the EGR valve can be cleaned, but a bad valve needs replacing. Valve replacement costs around $380 for parts and labor.

EVAP System Repair

Leaks in EVAP system hoses and valves will need to be located and sealed. Expect at least a few hours labor charge for diagnosis and repair.

Emissions Failure Impact On Performance

Driving with an emission system problem honda accord 2018 can have significant effects including:

  • Increase in harmful exhaust emissions
  • Reduction in engine power and acceleration
  • Decrease in gas mileage up to 15-20%
  • Engine overheating from inefficient fuel combustion
  • Increased wear and strain on engine components

Prolonged driving with an emissions issue will likely result in costly repairs down the road. It’s imperative to promptly address any indicated emissions system problems.

Is The Car Drivable With The Emissions Light On?

The Check Engine light accompanied by an emissions-related trouble code does not necessarily mean the 2018 Honda Accord is undrivable. However, driving should be limited only to essential trips while scheduling repairs.

While the car may seem to drive normally, emissions systems problems allow increased pollution and reduce performance. Driving extended distances can risk further damage.

Passing An Emissions Test With Emissions System Problems

A 2018 Honda Accord is highly unlikely to pass an emissions or smog check test if the check engine light is on for emissions-related issues.

Even if the car seems to drive fine, the on-board diagnostics will detect problems in the emissions components and cause an automatic test failure.

The car will need the indicated emissions system repaired before it has any chance of passing an emissions test. Expect repair costs to start around $200, but potentially much higher for catalytic converter replacement.

Maintaining Your Honda Accord Emissions System

Preventative maintenance is key to avoiding 2018 Honda Accord emissions system problems:

  • Regular oil changes
  • Replace air filters
  • Check engine light diagnosed promptly
  • Follow severe vs normal service schedule
  • Inspect oxygen sensor condition
  • Ensure proper tire pressure
  • Avoid ignition misfires

Following the manufacturer’s maintenance schedule will help minimize emissions system repairs and keep your Honda Accord running cleanly for years.

Can I Drive With Emissions Light On Legally?

Legally, a vehicle cannot be driven on public roads with the check engine light illuminated for emissions-related issues in many jurisdictions.

States with emissions testing programs will issue fines and citations to drivers operating a vehicle that would fail an emissions test.

Before driving a 2018 Honda Accord with the check engine light on for any length of time, make sure to check your local laws to avoid the risk of penalties.

How Do I Fix My Honda Emission System Problem?

When your Honda has an emissions system problem, the first step is to diagnose the specific issue. Connect an OBD-II scanner tool to read the diagnostic trouble codes stored in the engine computer. This will point you in the right direction.

Common causes include:

  • Faulty oxygen sensors – Will need replacement
  • Clogged catalytic converter – May need replacement
  • Carbon buildup on EGR valve – Clean or replace valve
  • Leaks in EVAP system – Need to be located and sealed

Once you’ve diagnosed the specific problem based on the trouble codes, repairs can be made. Replacement of the oxygen sensors, catalytic converter, EGR valve cleaning or replacement, and EVAP system leak repair are some typical fixes.

Use only Honda genuine parts when possible for repairs to ensure proper operation. In some cases, taking your Honda to a dealer may be best to allow proper diagnosis and repair by specialized technicians.

What Does It Mean When It Says Emissions System Problem?

When you see an “emissions system problem” message or the check engine light comes on in your Honda, it means there is a fault detected in one of the vehicle’s emissions control systems.

Potential causes include:

  • Leaking, disconnected or damaged vacuum hoses
  • Faulty oxygen sensors or heated oxygen sensors
  • Defective EGR valve or EGR solenoid
  • Clogged catalytic converter
  • EVAP system leaks
  • Bad spark plugs or ignition coil
  • Sticking PCV valve
  • Faulty fuel injectors

The emission system problem light is intended to alert you to have the indicated issues diagnosed and repaired promptly. Driving with a known emission problem can lead to increased emissions, reduced performance, and potential engine damage if left unattended.

Common Questions About 2018 Honda Accord Emissions Issues

What Are Some Signs Of An Emissions System Problem?

Reduced acceleration, poor fuel mileage, illuminated check engine light are signs of a potential emission system problem honda accord 2018. Unusual exhaust smells or visible smoke are also indicators.

Does A Bad Catalytic Converter Affect Performance?

Yes, a faulty catalytic converter will reduce performance and gas mileage of your 2018 Honda Accord. Replacing a bad catalytic converter often resolves these drivability issues.

Why Has My Honda Accord Failed Emissions Testing?

The most common reason for failing an emissions test in a 2018 Honda Accord is a faulty catalytic converter. Oxygen sensor issues, EVAP leaks, loose gas caps, and bad spark plugs may also cause test failure.

How Much Does It Cost To Repair Emissions Issues?

Costs vary considerably based on needed repairs. Simple fixes may be under $200, while catalytic converter replacement can be $1000 or more. Diagnosis is key to determine the problem.

How Long Can I Drive With Emissions Light On?

You should minimize driving with the check engine light on and schedule repair immediately. While it may seem to drive OK, emissions problems impact performance and economy while increasing pollution.


Emissions system problems in Honda vehicles should be addressed promptly when indicated. Diagnosing the specific issue via trouble codes allows proper repairs to be made. Taking quick action maintains performance, fuel economy, and reduces environmental pollution. Following recommended maintenance procedures helps prevent many emissions system repairs.

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Ammar Masoud

I have had a long and fulfilling career in the automotive industry, primarily with Honda and Acura. With 15 years of experience as a Honda service technician, I became highly skilled in repair and maintenance, gaining a deep understanding of these vehicles. After many years in the automotive field, I decided to embark on a second career in industrial manufacturing. It was a significant change, but I found that the skills I had honed in the automotive industry were incredibly valuable in my new role. In my current position in industrial manufacturing, the demand for quality workmanship and meticulous attention to detail is paramount. Fortunately, these are traits that I have cultivated throughout my years in the automotive industry. I take pride in applying these skills to meet the high standards expected in the manufacturing sector.