This guide will learn what Mazda check engine light (CEL) means, common causes, and how to diagnose Mazda CEL yourself.
DIY Cost: $15-$50
Est. Time: 30 min
What does it mean when the Mazda check engine light stays on?
Mazda check engine light will come on and stays on when the On-Board Diagnostic (OBD) system detects a malfunction with the engine, transmission, or the evaporative emission control (EVAP) system.
The check engine light on a Mazda can come on for something as simple as a loose gas cap, but it can also indicate serious engine or transmission problems such as a stretched timing chain or a faulty valve body.
The good news is that a fault code, also known as Diagnostic Trouble Code (DTC), is stored in the On-Board Diagnostic (OBD) system and can be read with an OBD-II scanner via the diagnostic port located under the dashboard on the driver's side. See the instructions in the next section.
What you may notice when your Mazda check engine light comes on:
Engine runs rough
The car won't respond to the accelerator pedal.
Check engine light flashes, and traction control light comes on.
Car shakes due to a misfire.
Lack of power
Poor throttle response
Unusual engine sound
Smoke from the exhaust
A decrease in fuel economy
Sometimes there are no symptoms, and the solution may be as simple as tightening a loose gas cap. Once the gas cap is tightened, it can take up to three days for the light to reset on its own, as long as there are no other fault codes.
Diagnose Mazda Check Engine Light
To find out the fault codes that triggered the check engine light to stay on, read the Diagnostic Trouble Codes (DTCs) with an OBD-II scanner would be the next step.
Locate the OBD-II port under the dashboard.
Plug the scanner into the OBD-II port.
Turn on the ignition but do not start the engine.
Turn on the scanner and select OBD-II.
Select READ FAULT CODES from the main menu.
The fault code is only the starting point for diagnosing the check engine light on a Mazda. Research each code and keep in mind that many issues can trigger one code.
Auto parts stores such as Advance Auto Parts, Autozone, PepBoys, O'Reilly may read your Mazda check engine codes free of charge.
Common Mazda Problems
Here are some common problems that trigger Mazda's check engine light to come on. Every situation is different, so you should read the codes to determine why the CEL light is on in your Mazda.
1. Timing Chain
Engines with a variable valve timing (VVT) sometimes suffer from over retarded timing. In most cases, this is caused by a dirty VVT filter screen. It gets clogged by a sludged oil. Another possibility is a faulty solenoid. Mazda CX-7 had a lot of problems with stretched timing chains. Codes: P0012 and P0014
Another common problem is a check engine light caused by low coolant temperature. In this case, a thermostat that is stuck in an open position is a probable cause.
The result is an engine that is not able to reach operating temperature. Common on Mazda 3 where check engine light is on, and code P0126 is present.
3. Mass Air Flow Sensor
Your engine is likely running lean if you are experiencing rough idle, lack of power, or hesitation on accelerations. This is usually caused by a dirty MAF sensor, which gives false air flow readings. This is another common problem with high mileage Mazda3 and Mazda 6 models.
Don't use anything else than MAF cleaner fluid for cleaning. Another possibility is an intake leak.
Code: P 0171
4. Evaporative Emission Control System Leak Detected
Your Mazda might have a check engine light on that is, in some cases, accompanied by a strong gas odor. This is usually caused by an evap system leak.
The purge valve is the first thing that needs to be checked for leaks and fuel ventilation lines. If they don't show any symptoms of deterioration, you should check the fuel tank pump union nut.
On some models, they can break as time goes by. Typical fault code: P0455
5. Oxygen Sensor
If you drive a higher-mileage Mazda, you will likely encounter an emission control that caused check engine light. Although this will be signaled as a catalytic converter low efficiency, you easily have faulty downstream oxygen (O2) sensor.
Make sure to rule this out before changing a much more expensive catalytic converter.
Codes: P0420 to P0431 (Catalyst Efficiency Below Threshold)
6. Carbon Buildup
Direct injection engines are prone to carbon build-up on intake valves. This can cause all sorts of engine running problems and give some misleading error codes. For instance, you might have a misfire or poor throttle response.
7. Vacuum Leak
Most newer Mazda engines have variable intake geometry manifold. Geometry variation is performed by swirl flaps that direct the stream of intake flow. This system is controlled by ECU and vacuum operated.
You might have problems related to this system if the solenoids get stuck. It is also possible for vacuum hoses to break. Also, to check the engine light, you might notice power loss and hesitation on acceleration.
Codes: P2004 and P2009 (Intake Manifold Runner Control)
8. Spark Plugs
If you have over 100,000 miles on the original spark plugs, it is time to change them. A bad spark plug, ignition coil, or spark plug wire can cause the Mazda check engine on plus engine misfire, which causes the car to shake.
Codes: P0300 P0301 P0302 P0303 P0304 P305 P0306 will be present.
Mazda Check engine light Flashing
If your Mazda check engine light is flashing, it indicates a misfire on one or more cylinders.
In addition to the check engine, light flashing the traction control light may also come on. Newer Mazda vehicles will go into limp mode once the check engine light starts to flash. In limp mode, the transmission will no longer shift, and there is reduced power.
Common causes include:
Bad ignition coil
Worn spark plugs
Damaged wire harness
Blown head gasket
Catalytic converter problem
Driving with the check engine light flashing can cause damage to the engine and catalytic converter.
Install new spark plugs if your Mazda has over 100,000 miles and the spark plugs have never been changed.
If you are getting misfire for only one cylinder, you may have a bad coil on that cylinder. For example, if you have fault code P0301, you have a misfire on cylinder 1, which could be due to a bad coil on that cylinder.
Wrench Light vs. Check Engine Light
The wrench light on a Mazda means that your vehicle is due for route maintenance. The maintenance light is not the same as the check engine light.
Your Mazda may be due for an oil change, air filter replacement, spark plug replacement, tire rotation, etc.
Mazda wrench light does not trigger the check engine light to come on.
Once you perform the required maintenance, you will need to reset the maintenance light.
Turn the ignition key to the ON position without starting the engine. Turn the key to position II or press the Start button twice without pressing the brake pedal.
Continue to hold down the TRIP knob until the wrench light starts to flash.
This guide applies to 1996 and newer Mazda vehicles, including Mazda 2, 3, 5, 6, MX-5 Miata, 626, CX-5, CX-7, CX-9.
Frequently Asked Questions
What can cause rough idle and poor fuel economy in my Mazda?
The first thing to check would be a coolant thermostat, as they can get stuck in an open position. In that case, the engine will not reach the operating temperature. Another option is a dirty MAF sensor that gives false air intake readings or an intake manifold leak.
My Mazda has VVT codes even after replacing solenoids? How is this possible?
VVT system has an oil screen, similar to the oil filter, which protects it from eventual debris or oil sludge. This screen can get very dirty, obstructing oil flow to the VVT actuators powered by oil pressure. The best way to prevent this is regular oil changes and using high-quality oil.
What does the wrench light mean on a Mazda?
The wrench indicator light means that your Mazda is due for route service. The wrench is not related to the check engine light. For example, the wrench can mean that your Mazda requires tire rotation, an oil change, or other maintenance work.
Will check engine light reset itself?
Mazda check engine light can reset on its own if the problem is no longer present. For example, if the light came on because you forgot to tighten the gas cap. The light will reset on its own within 3 to 4 days after you tighten the gas cap. If the light remains on, the problem is still present.
Do you have to reset the check engine light after repair?
No. You can drive the car, and within 3 to 4 days, the light will reset on its own. Assuming all the problems have been fixed.