Mitsubishi Check Engine Light Stays On

Mitsubishi's service engine soon, also known as a check engine light, can come on when the On-Board Diagnostic (OBD) system detects a problem with the engine, emission system, and/or transmission.

DIY Cost: $20-$150
Est. Time: 30 min - 2 hr
Difficulty: Intermediate

If your Mitsubishi check engine light stays on, first check that the gas cap is on tight.

If that is not the problem, read the fault codes by connecting an OBD2 scanner to the diagnostic port located under the dashboard. See the instructions below. 

Mitsubishi service engine soon light on

On some Mitsubishi models, the check engine light may come on instead of the service engine soon. Both these lights serve the same functions.

'Check engine light' and the 'service engine soon' messages should not be confused with Routine Maintenance. They are required messages which are meant to remind the driver of regular maintenance.


What you may notice when your Mitsubishi service engine soon light comes on:

  • Mitsubishi runs rough
  • Engine misfire or juddering
  • Lack of power
  • Poor throttle response
  • Unusual sound from the engine
  • Smoke from the exhaust
  • Overheating
  • Engine idles too high.
  • The engine dies soon after it is started.

These symptoms indicate that the engine in your car is not working as it should.

If your Mitsubishi service engine soon light is on, but the car runs and drives fine, the problem could be due to an evaporative leak in the fuel system or a loose gas cap.

What Causes Mitsubishi Check Engine Light?

bad spark plugs trigger mitsubishi lancer service engine soon light to stay on

The most common problems that trigger the Mitsubishi check engine or service engine's soon light are faulty oxygen sensor, dirty mass airflow sensor (MAF), worn spark plugs, bad ignition coil, and loose gas cap.

There are hundreds of possible issues that can turn on the check engine light on a Mitsubishi vehicle. To find out why the light is on, read the fault codes with an OBD-II scanner

1. Spark Plugs

bad spark plug

Old spark plugs will cause your Mitsubishi check engine light to come on with fault codes P0300, P0301, P0302, P0303, P0304.

Also, they can cause your vehicle to have reduced power and a decrease in fuel economy. Keep in mind that driving with bad spark plugs may damage your catalytic converter and oxygen sensors.

Faulty spark plugs are a common problem that triggers the check engine light on Mitsubishi cars. The problem is generally not the manufacturer's fault but lacks maintenance on the owner's part. Spark plugs are maintenance items and need to be replaced as the car nears the 100k mile mark.

Check your owner's manual for the specific recommended spark plug replacement interval.

2. Mass Air Flow Sensor

The engine in your Mitsubishi has, in most cases, an integrated MAF sensor and intake air temperature sensors. With time, it can get contaminated with dirt, giving false readings. This will result in rough idle, lack of power, or hesitation on accelerations.

Cleaning the sensor is quite simple but only use MAF cleaner fluid for this job.

Another possibility is an intake leak. Codes: P0102 (Mass airflow sensor), P0113 (Intake air temperature sensor)

3. Coolant Temperature Sensor

Some Mitsubishis are somewhat more prone to coolant temperature sensor issues. A faulty CTS will give false temperature readings, causing, in most cases, the engine to run rich.

Also, it will show the incorrect and misleading temperature reading on your dashboard. In addition to the sensor itself, make sure the wiring is not damaged. Code: P0115 (Coolant temperature sensor malfunction)

4. Vacuum Leak

All turbocharged engines, and especially diesel ones, can suffer from under-boost. This is a situation where the desired boost pressure is not reached. It can be caused by a massive intake leak or a crack at vacuum hoses that regulate the turbo. Another possibility is an excessive carbon build-up inside the intake manifold.

This problem may trigger fault code P0299 (Boost pressure regulation control range not reached).

5. EVAP Leak

A small leak with the EVAP system is a widespread problem.

The first thing to check is if the fuel tank cap is loose. Other possibilities are cracks in EVAP hoses, vapor canisters, faulty purge, or canister vent valves. The best way to find a fault is to test the whole system with a smoke generator machine.

This problem may trigger the fault code P0456 (Evaporative Emissions System - Small leak detected)

6. Emission Issue

A check engine light caused by emission control-related issues is something you are likely to encounter if you drive a higher-mileage Mitsubishi.

Although this will be signaled as a catalytic converter with low efficiency, you easily have a faulty downstream O2 sensor. Make sure to rule this out before changing a much more expensive catalytic converter.

This problem may trigger fault codes P0420 or P0431 (Catalyst Efficiency Below Threshold).

7. Transmission Problem

Transmission issues in cars equipped with a CVT gearbox are usually caused by a faulty transmission fluid pressure switch, which controls the torque converter solenoid operation. As this switch is installed on the outer side of the gearbox, it can be easily replaced.

This problem may trigger the fault code, P0842 (transmission fluid pressure switch circuit low).

8. Throttle Position Sensor

The throttle position sensor (TPS) monitors how far the throttle valve (or blade) is open, determined by how far down the accelerator pedal has been pushed. The TPS can fail to trigger the check engine light. In addition, you may notice erratic idle or the engine shutting down at low RPMs. 

If you have determined that the trouble is caused by the faulty TPS, you may follow these steps to replace it. 1. Let the engine cool down. 2. Place the car in park. 3. Pop the hood. 4. Take out the air hose by removing the clamp and 4 screws. 

remove air hose

5. Once you pulled out the air hose, you will have an unrestricted view of the TPS.

location of TPS

6. You can now remove it, replace it with a new one, and re-connect the air hose.

Please note that you may need to perform a re-programming and re-learn after installation. These can be done using a Mitsubishi OBD2 scan tool.

9. DPF (Diesel models)

Most 2007 or newer Mitsubishis with diesel engines have a Diesel Particulate Filter or DPF. This is a device that traps the soot from the exhaust.

It can get clogged over time, resulting in high temperatures and excessive back-pressure. In most cases, the build-up can be burned off by triggering a regeneration process.

This problem may trigger fault code: P1499 (DPF temperature abnormally high).

How to Reset Mitsubishi Check Engine Light?



When the check engine light comes on, a trouble code will be sent to the ECU. 

Use an OBD-II scanner to read the codes via the diagnostic port under the driver's side dashboard.  

  1. Plug an OBD-II scanner into the diagnostic port under the dashboard. 
  2. Turn on the ignition but don't turn on the engine. 
  3. Turn on the scanner and select Read Fault Codes. Find out what caused each code and fix all problems. 
  4. Go back to the main menu and select Clear Fault Codes, then press ok. 

Once the repair has been made, the code can be erased. Most OBD2 scanners and all scan tools can do this with the press of a button.

All 1996 and later Mitsubishi vehicles are equipped with an OBD-II diagnostic system.

Mitsubishi Check Engine Light Flashing On and Off

If your Mitsubishi check engine light is flashing, avoid driving for an extended time. Doing so will damage the catalytic converter and even lead to the engine overheating.

Flashing service engine soon light means that there is an engine misfire, which in most cases is caused by a faulty spark plug or bad ignition coil. 

Can a Loose Gas Cap Trigger a Check Engine Light? 

If your Mitsubishi check engine light came on after refueling, there is a good chance that you have a loose gas cap or poor fuel quality. 

A loose or missing fuel cap on a Mitsubishi can trigger the check engine light because it makes the On-Board Diagnostic system think there is a problem with the fuel system.

Tighten the gas cap or replace it, but don't expect the check engine light to reset immediately. It may take two to four days for the check engine light to reset on its own.


If your Mitsubishi check engine light stays on, first check that the gas cap is on tight. Tighten the gas cap. If no other codes are present, the check engine light will reset within two to three days of normal driving. 

If the check engine or service engine soon lights stay on, read the fault codes by connecting an OBD2 scanner into the diagnostic port located under the dashboard.

Always research the code and possible causes. Don't replace parts based on the fault code alone. Get a second opinion from a mechanic if necessary.

If you are the original owner, your Mitsubishi is less than 10 years old and has less than 100,000 miles. Your car may still be under warranty. A Mitsubishi dealer should diagnose and fix your problem free of charge.

This guide applies to all 1996 and newer Mitsubishi vehicles, including Lancer, Montero, Outlander, Galant, Eclipse, Raider, Pajero, Mirage, etc.