If your vehicle’s check engine light comes on and you see an emission-related diagnostic trouble code (DTC), it’s important to address the issue as soon as possible.
Ignoring the problem can lead to reduced fuel efficiency, increased emissions, and potential damage to your vehicle’s engine components.
In this article, we’ll explore how to fix emission-related engine DTCs, including some common causes of these codes and the steps you can take to resolve them.
Symptoms of Emission-Related DTCs
The symptoms of an emission-related diagnostic trouble code (DTC) can vary depending on the specific code, but some common symptoms may include:
- Check engine light on
- Poor acceleration
- Rough idle
- Excessive fuel consumption
- Odd smells coming from the exhaust pipe
- Increased emissions levels (as indicated by a tailpipe test)
Check engine light on:
The first, and most obvious, symptom of an emission-related DTC is the check engine light being illuminated on your dashboard.
This indicates that something is wrong with the vehicle’s emissions system and should be investigated further.
Poor acceleration:
Poor acceleration is another common symptom of an emission-related DTC.
If the vehicle is sluggish when accelerating, it could be due to an issue with the fuel system or a clogged catalytic converter.
Rough idle:
If your vehicle struggles to maintain consistent engine RPMs and shakes or vibrates at low speeds, this could indicate a problem with your spark plugs or other components of the emissions system.
Excessive fuel consumption:
If you’re noticing that your car’s fuel economy has decreased significantly, this could point to an issue with the emissions system.
This can include everything from bad spark plugs to a faulty oxygen sensor.
Odd smells coming from the exhaust pipe:
Finally, if you smell a pungent, acrid odor coming from your vehicle’s exhaust pipe, this could indicate an issue related to the engine’s emissions system.
Increased emissions levels:
If you get your car tested at a tailpipe test facility and find that it exceeds the allowed emission limits, this could be caused by one of several issues in the emissions system.
Common Causes of Emission-Related DTCs:
- Faulty oxygen sensor
- Exhaust gas recirculation (EGR) valve or EGR tube clogged or stuck
- Leaking fuel injectors
- Malfunctioning catalytic converter
- Clogged air filter or air flow meter
- Vacuum leaks in the intake manifold or vacuum line/hose connections
- Defective spark plugs or ignition coils
Faulty oxygen sensor:
A faulty oxygen sensor is one of the most common causes of emission-related DTCs.
The oxygen sensor measures how much oxygen is present in the exhaust system and sends a signal to the engine control unit (ECU) so it can adjust the air/fuel mixture accordingly.
If this sensor is not working correctly, it may cause an incorrect fuel trim or other faults resulting in increased emissions.
Exhaust gas recirculation (EGR) valve or EGR tube clogged or stuck:
The exhaust gas recirculation (EGR) system helps reduce pollutants from entering the atmosphere by cycling some of the exhaust back into the intake manifold where it can be burned again.
When this valve sticks open, increased amounts of unburned fuel will enter the exhaust system, resulting in increased emissions.
Additionally, if the EGR tube becomes clogged or blocked for any reason, it will also cause an increase in emissions.
Leaking fuel injectors:
Fuel injectors are responsible for injecting precise amounts of fuel into the engine cylinders.
If one or more of these injectors become damaged or worn out, they may start to leak fuel into the intake manifold and then on into the exhaust system.
This can lead to an increase in hydrocarbon emissions and other pollutants being expelled from your vehicle.
Malfunctioning catalytic converter:
The catalytic converter is a device that helps reduce harmful gases such as carbon monoxide (CO) and nitrogen oxides (NOx) from exiting the exhaust.
If this part becomes damaged or clogged due to age or improper maintenance, it can cause an increase in emissions.
Clogged air filter or air flow meter:
If the air filter or air flow meter is clogged with dirt and debris, it can reduce the amount of clean air that enters the engine which can lead to increased hydrocarbon emissions as well as other pollutants.
It is important to regularly check these components and replace them when they become dirty or worn out.
Vacuum leaks in intake manifold or vacuum line/hose connections:
The vacuum system helps regulate many different parts of a vehicle such as the EGR system, fuel injectors and the transmission.
If there is a leak in the intake manifold or any of the vacuum line/hose connections, it can cause an increase in emissions as well as other drivability issues.
Defective spark plugs or ignition coils:
Defective spark plugs or ignition coils can lead to incomplete combustion which can result in increased hydrocarbon emissions from your vehicle.
It is important to inspect these components regularly and replace them when necessary to ensure optimal performance and compliance with emission standards.
Most Common Emission-Related Diagnostic Trouble Codes
Common emission-related Diagnostic Trouble Codes (
DTCs) include P0135, P0420, P0430, P1456, P0401, P0402, P0421, P0431, and P0455.
But here is the list of Diagnostic Trouble Codes:
| Code | Meaning |
|---|---|
| P0100-P0105 | Mass or Volume Air Flow Circuit Malfunction |
| P0110-P0115 | Intake Air Temperature Circuit Malfunction |
| P0120-P0123 | Throttle/Pedal Position Sensor/Switch A Circuit Malfunction |
| P0130-P0167 | Oxygen Sensor Circuit Malfunction (Bank 1 and Bank 2) |
| P0170-P0175 | Fuel Trim Malfunction (Bank 1 and Bank 2) |
| P0180-P0183 | Fuel Temperature Sensor A Circuit Malfunction |
| P0190-P0194 | Fuel Rail Pressure Sensor Circuit Malfunction |
| P0200-P0214 | Injector Circuit Malfunction (Cylinder 1-14) |
| P0220-P0229 | Throttle/Pedal Position Sensor/Switch B Circuit Malfunction |
| P0230-P0238 | Fuel Pump Control Circuit Malfunction |
| P0240-P0245 | Turbocharger Boost Sensor Circuit Malfunction |
| P0261-P0269 | Cylinder 1-3 Contribution/Balance Fault |
| P0270-P0278 | Cylinder 4-6 Contribution/Balance Fault |
| P0280-P0288 | Cylinder 7-8 Contribution/Balance Fault |
| P0300-P0315 | Random/Multiple Cylinder Misfire Detected (Cylinder 1-15) |
| P0320-P0328 | Knock Sensor Circuit Malfunction (Bank 1 and Bank 2) |
| P0330-P0335 | Crankshaft Position Sensor Circuit Malfunction |
| P0340-P0345 | Camshaft Position Sensor Circuit Malfunction (Bank 1 and Bank 2) |
| P0360-P0365 | Camshaft Position Sensor B Circuit Malfunction (Bank 1 and Bank 2) |
| P0400-P0409 | Exhaust Gas Recirculation (EGR) System Malfunction |
| P0440-P0455 | Evaporative Emission Control System Malfunction |
| P0500-P0507 | Vehicle Speed Sensor Circuit Malfunction |
| P0560-P0564 | System Voltage Malfunction |
| P0600-P0609 | Control Module Communication Bus Off |
| P0620-P0629 | Generator Control Circuit Malfunction |
| P0640-P0645 | Intake Air Heater Control Circuit Malfunction |
| P0650-P0670 | Glow Plug Control Circuit Malfunction (Cylinder 1-8) |
| P0680-P0689 | Glow Plug Control Module to PCM Communication Circuit Malfunction |
| P0700-P0705 | Transmission Control System Malfunction |
| P0710-P0717 | Transmission Fluid Temperature Sensor Circuit Malfunction |
| P0720-P0729 | Output Speed Sensor Circuit Malfunction |
| P0730-P0738 | Incorrect Gear Ratio |
| P0740-P0746 | Torque Converter Clutch Circuit Malfunction |
| P0750-P0777 | Shift Solenoid Malfunction (Shift Solenoid A-E, Transmission Control Solenoid A-D) |
| P0800-P0899 | Transmission Control System Malfunction (TCM) |
| P1120-P1129 | Throttle Position Sensor Circuit Malfunction |
| P1130-P1135 | Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 1 and Bank 2 Sensor 1) |
| P1170-P1175 | Fuel Trim Adaptation Additive Malfunction (Bank 1 and Bank 2) |
Tools Needed for Fixing Emission-Related DTCs
In order to properly diagnose and repair emission-related DTCs, you may need to have the following tools and/or diagnostic equipment on hand:
- OBD-II Scanner or Code Reader
- Digital multimeter
- Screwdrivers and wrenches
- Socket set
- Pressure tester
- Vacuum pump
- O2 sensor test kit
- Gas analyzer
- Smoke machine
- Exhaust gas analyzer
- Tailpipe smoke analyzer
- Fuel injector cleaning kit
- Compression tester
- Engine degreaser
- Catalytic converter
- Heat gun
How to fix emission-related engine DTCs
Retrieve the code:
The first step in fixing an emission-related engine DTC is to retrieve the code from the vehicle’s computer.
This can be done using an OBD-II scanner, which plugs into the OBD-II port typically located underneath the dashboard on the driver’s side.
The scanner will display the code, which is typically a five-digit alphanumeric string that indicates the type of issue that the engine is experiencing.
Determine the cause:
Once you have the code, you need to determine the underlying cause of the problem.
There are many potential causes of an emission-related engine DTC, including issues with the oxygen sensors, the catalytic converter, the evaporative emission control system, the exhaust gas recirculation system, or the engine itself.
Depending on the specific code that you have retrieved, there may be specific diagnostic procedures that you can follow to pinpoint the problem.
You can also consult the vehicle’s service manual for guidance.
Perform diagnostic tests:
To determine the root cause of the issue, you may need to perform additional diagnostic tests.
These can include visual inspections of the engine components, using a multimeter to test electrical connections, and using a scan tool to monitor live data from various sensors.
You may also need to perform more advanced diagnostic tests, such as a smoke test to check for leaks in the evaporative emission control system, or a compression test to check the engine’s compression levels.
Repair the problem:
Once you have identified the underlying cause of the problem, you can begin to repair it.
This may involve replacing a faulty sensor, repairing damaged wiring, replacing a clogged catalytic converter, or repairing a damaged or malfunctioning engine component.
It is important to follow the manufacturer’s instructions when repairing the issue and to use high-quality replacement parts to ensure that the repair is effective.
Clear the code:
After you have repaired the problem, you need to clear the DTC from the vehicle’s computer.
This can be done using an OBD-II scanner. Clearing the code will reset the check engine light and allow you to determine whether the problem has been fully resolved.
Verify the fix:
Once you have cleared the code, you need to verify that the issue has been fixed.
This can be done by driving the vehicle and monitoring the check engine light to ensure that it does not come back on.
You may also want to use an OBD-II scanner to monitor the vehicle’s emissions data to ensure that it is within acceptable limits.
If the issue has not been fully resolved, you may need to repeat some of the diagnostic tests or consult a professional mechanic for further assistance.
How to prevent Emission-Related DTCs:
Keep up with regular vehicle maintenance:
Regular maintenance, such as oil changes and tune-ups, can help prevent engine-related DTCs by ensuring that your vehicle is operating at optimal performance.
Use quality fuel and oil:
Low-quality fuel and oil can lead to a buildup of deposits in your engine, which can trigger DTCs related to the oxygen sensors, fuel trim, and other components.
Check your gas cap:
A loose or faulty gas cap can trigger a DTC related to the evaporative emission control system. Make sure your gas cap is properly secured and in good condition.
Avoid excessive idling:
Excessive idling can lead to incomplete combustion and the buildup of carbon deposits in the engine.
This can trigger DTCs related to the oxygen sensors, fuel trim, and other components.
Drive at moderate speeds:
Aggressive driving can put additional stress on your engine and lead to increased emissions. Try to drive at moderate speeds and avoid rapid acceleration or braking.
Keep your engine in good condition:
Any issues with your engine, such as a misfiring cylinder or a faulty sensor, can trigger a DTC. Be sure to address any engine issues as soon as possible.
Check engine codes promptly:
If your check engine light comes on, it’s important to get the codes read and addressed promptly.
Ignoring a DTC can lead to additional damage and increased emissions.
Conclusion
Emission-related DTCs can be tricky to diagnose and repair, but by taking the proper steps and having the right tools on-hand, they can be easier to address.
Always remember to keep up with regular vehicle maintenance and pay close attention to your check engine light if it comes on.
If you keep these things in mind, you can help prevent and address emission-related DTCs.
