Mitsubishi Check Engine Light

Mitsubishi service engine soon ( also known as check engine light) comes on when the engine computer, known as the On Board Diagnostic (OBD) system, detects a problem with the engine, emission system or drivetrain.

Service engine soon light does not necessarily mean that you have a big expensive problem. With that said, don't ignore Mitsubishi service engine soon light even if your car drives fine. 

On some Mitsubishi models, check engine light may come on instead of service engine soon. Both these lights serve the same functions. They should not be confused with Routine maintenance required message which is meant to remind the driver of regular maintenance. 

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

Symptoms

Mitsubishi service engine soon light on

What you 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 to high 
  • Engine dies soon after it starts

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 evaporative leak in the fuel system or a loose gas cap

What to do?

The main problem with check engine an service engine soon light is that it does not tell much on it own.

If your Mitsubishi check engine light is flashing, avoid driving for an extended time as doing so could cause damage to the catalytic converter and even may lead to the engine overheating. Flashing service engine soon light means that there is an engine misfire.

In most cases Mitsubishi when the check engine light is constantly on, your Mitsubishi will drive fine. If that is the case, follow these troubleshooting steps. 

Check Fuel Cap

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If your Mitsubishi check engine light came on after fueling, there is a good chance that you have a loose gas cap. A loose or missing fuel cap on a Mitsubishi can trigger the check engine light to come on 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. 

Monitor Vehicle Operation

mitsubishi warning lights

Ensure that no other warning lights on. Pay close attention to the engine temperature. Do not drive if the car starts to overheat.

Also, pay close attention to the oil pressure light. Even though very unlikely to happen, if the oil light comes on immediately pull over and turn off the engine. 

Read Fault Codes

diagnose read fault codes mitsubishi service engine light soon on

The most reliable way for figuring out the source of the problem is using an OBD2 scanner to display the diagnostic trouble codes stored in the system.

When the check engine light comes on a trouble code would be set in the computer. So even if the light goes out or comes on intermittently, the computer will remember the problem. All 1996 and later cars are equipped with the OBD2 diagnostic system, that uses the same method for reading codes and the same code lists.

The trouble codes can be retrieved with devices that range from simple code readers to sophisticated scan tools. All of them plug into the diagnostic port which is located under the driver's side of the dashboard.

To read any stored codes, plug in the OBD2 scanner and turn the ignition on.

After obtaining trouble codes, you will be able to track down the faulty component. Once the repair has been made, the trouble code can be erased. Most OBD2 scanners and all scan tools are able to do this with the press of a button. 

Keep in mind that a scanner that can read Mitsubishi specific fault coedes will provide better fault code descriptions and may even retrieve more codes than a generic OBD2 scanner

Common Causes

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

Here is a list of the common problems that trigger Mitsubishi service engine light to come on.

Spark Plugs

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 decrease in fuel economy. Keep in mind that driving with bad spark plugs you 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 a lack of maintenance on the owners part. Spark plugs are maintenance items and need to be replaced as the car nears 100 000 mile mark. Check your owners manual for the recommended spark plug replacement interval. 

Follow this guide on how to replace spark plugs on Mitsubishi four-cylinder engine

Mass Air Flow Sensor

The engine in your Mitsubishi has, in most cases, an integrated MAF 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 air flow sensor), P0113 (Intake air temperature sensor)

Coolant Temperature Sensor

Some Mitsubishis are somewhat more prone to coolant temperature sensor issues. A faulty CTS will give false temperature reading, causing in most cases engine running 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)

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). 

Smap 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 or vapor canister or a faulty purge or canister vent valves. Best way to find a fault is to test the whole system with a smoke generator machine.

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

Emission Related

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

Although this will be signaled as a catalytic converter low efficiency, it is easily possible that you have a faulty downstream o2 sensor. Make sure to rule this out before changing much more expensive catalytic converter.

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

Transmission Problem 

Transmission issues in cars that are 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 is easily replaced.  

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

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 temperature 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).

Conclusion

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 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 and 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.

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