Toyota Check Engine Light Stays On

Toyota check engine, or service engine soon light, may come on due to something as simple as a loose gas cap.

Est. Time: 30 min - 2 hr
Difficulty: Intermediate

Toyota check engine, or service engine soon light, may come on due to something as simple as a loose gas cap.

It can also indicate many other issues, including bad spark plugs, faulty oxygen sensors, dirty mass airflow sensors, and even an early indication of a transmission problem. 

This guide will learn about common problems that trigger Toyota check engine lights and how to diagnose Toyota check engine light yourself using an OBD2 scanner.

What does the Toyota check engine light mean? 

Check engine light Toyota

If your Toyota check engine light comes on, it means that the engine could be misfiring, a broken oxygen sensor, or simply a loose gas cap.

When you see the check engine light come on in a Toyota, it doesn't mean you need to pull the car over to the side of the road and call a tow truck unless the check engine light is flashing. Get the vehicle checked out as soon as possible.


In addition to the check engine light, you may get other warnings such as VSC and Trac Off coming on.

Other common symptoms that you may notice include:

  • Engine runs rough

  • Traction Light or VSC Light comes on.

  • Check Engine Light flashes when accelerating.

  • Engine misfires or shakes

  • Lack of power

  • Poor throttle response

If you are experiencing any of the described symptoms, it is an indication that your engine is not running as it should.

To find out what is wrong with your Toyota, read the fault codes with an OBD-II scanner

See the step-by-step instructions and video in the next sections. 

How to Diagnose Toyota Check Engine Light

Use an OBD-II scanner to read the fault codes via the diagnostic port located under the dashboard. 

  1. Locate the OBD2 port under the obd2 port locaiton
  2. Plugin your OBD2 scanner. Turn on the ignition but do not start the engine on
  3. Please turn on the scanner and let it communicate with the car—Select Read Codes from the main menu.
  4. Press enter, and fault codes will display on the screen. Scroll to see all the codes. Make sure to check Current, Pending, and Permanent codes.

Write down all the codes and research all codes online. 

Don't start replacing parts on your Toyota based on the fault code only.

Consult a mechanic for advice if necessary.

Common Problems That Trigger the Check Engine Light on a Toyota

Toyota check engine light can come on for many reasons.

Let's take a look at common problems that trigger the check engine light on a Toyota.

1. Bad Spark Plugs or Ignition Coil

ignition coil

Toyota vehicles require spark plugs to be changed between 90,000 and 120,000 miles.

If you don't change your Toyota spark plugs at this interval, they will eventually fail and cause the check engine light to come on.

Also, you will most likely get an engine misfire where the engine starts to shake.

2. Mass Air Flow Sensor

Toyota check engine light on due to bad MAF sensor

Your engine is likely running lean if you are experiencing rough idle, lack of power, or hesitation on accelerations. Most Toyota engines have mass airflow sensors.

This adds some complexity, and a possible vacuum leak makes throws off readings from the MAF.

Another usual problem is a false reading from a dirty MAF sensor.

Don't use anything else than MAF cleaner fluid for cleaning. Code: P0171.

3. Loose Fuel Cap

Toyota check engine light turned on by loose gas cap

Check engine light on Toyota Camry, Corolla, Sienna, 4Runner, Highlander, Matrix, Avalon, Rav4, etc., can come on if you don't tighten the gas cap.

Find a safe place to pull over.

Check that you have installed the gas cap.

If the gas cap is installed, tighten it. The check engine light will not turn off immediately.

It can take up to three days for it to reset on its own. 

4. Timing Chain

Timing Chain

Check engine light on Toyota Camry, 4Runer, Highlander with V6 engines can be due to a stretched timing chain.

Although designed as a life-long item, they can overstretch, or tensioner failures are possible.

This can cause timing-related issues and corresponding engine error codes.

Typically not an issue unless your Toyota has over 200,000 miles and the timing chain has never been replaced.

Most Toyota engines have variable valve timing (VVT).

The aforementioned oil sludging and poor maintenance, in general, usually have a negative impact on it.

In most cases, it is a VVT filter screen that gets clogged by a sludged oil.

Another possibility is a faulty solenoid. Codes: P0012 and P0014.

5. Oxygen Sensor 

Toyota Engine

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

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. Codes: P0420 to P0431.

6. Engine Sludge

Many Toyotas made in the 2000s are affected by oil sludging caused by a blocked crankcase ventilation valve (aka PCV valve).

This can cause various problems ranging from high oil consumption, rough idle or a check engine light, and even a complete engine failure at highway speeds.

A telltale sign is a cloud of blue smoke on startup or acceleration.

You could also get emission control-related codes, such as P0420.

7. Idle Air Control System

If you have an older Toyota with a cable-operated throttle, you might have problems with the Idle air control system. In most cases, the idle air control valve gets dirty or blocked by carbon build-up.

This can be solved by detail cleaning with carb cleaner. It is also possible for a throttle position sensor to fail.

Symptoms include rough idle and hesitation when accelerating from idle. Code P0505

8. Vehicle speed sensor failure

Although generally very reliable, Toyota is well known for vehicle speed sensor failure.

This will trigger a check engine light, combined with ABS/TC/Cruise lights.

But the speedometer that doesn't work is the definite sign of a vehicle speed sensor problem.

The sensor is located at the gearbox output side.

Make sure you check the wiring and connector for damage. You will usually get the code P0500.

9. Crankshaft position sensor

If you are experiencing a sporadic crank without a start situation, or your Toyota cuts out without any apparent reason, you might have a bad crankshaft position sensor.

Before replacing the sensor itself, carefully examine the wiring, as it can suffer from heat damage—code P0335.

Toyota Check Engine is Flashing

Toyota check engine light may flash when accelerating or at idle.

In addition to the check engine light blinking, the engine will shake as well.

These symptoms indicate an engine misfire on one or more cylinders.

Driving with a Toyota check engine light blinking could damage a catalytic converter and cause the engine to overheat.

Restarting the engine or easing on the throttle may help your engine regain normal operation.

We do not recommend you drive your Toyota if the check engine light is blinking.

What does VSC and Check Engine Lights mean on a Toyota

toyota check engine vsc light on

A common issue with many Toyota vehicles is that in addition to the check engine light, the VSC OFF light may also come on.

VSC means Vehicle Stability Control. Also, traction control or Trac Off light may come on as well.

If that is the case, it doesn't necessarily mean a problem with your Toyota traction control system. It simply means that the system is disabled and will not work until the check engine light problem is fixed.

The downside of having VSC Off or Trac Off is that your vehicle may skid under extreme driving conditions.

Toyota VSC Off & Check Engine Lights can be triggered from something like a loose gas cap. The only way to know for sure is to read the codes with an OBD2 scanner.

Trac Off and Check Engine Light on Toyota

Toyota engine trac off light

It is common for the traction control light to come when the check engine light on your Toyota comes on.

The traction control gets disabled, but that doesn't mean a problem with the Trac system.

Just fix the check engine light problem, and your Trac Off light will reset as well.

What to do if the Toyota check engine light comes on? 

toyota check engine

Toyota check engine light may come on for many reasons.

Check that the gas cap is on and tight. Find a safe place to park. Turn off the engine, set the parking brakes. Open the fuel door and ensure the gas cap is on tight.

Turn the gas cap clockwise until you hear it click several times. Your check engine light will reset on its own within two to three days.

An OBD2 scanner can reset the Toyota check engine light as long as there are no other issues present.

If the light doesn't reset within a couple of days, the next step would be to read the fault codes with an OBD-II scanner. 

You may continue your journey if you don't notice any performance issues and the check engine light is not flashing.

In some cases, the Toyota check engine light may come on with no other symptoms. The problem most likely is emissions-related.

Keep in mind that the vehicle may have increased emissions and fuel consumption. Don't ignore your Toyota check engine light even if there are no apparent performance issues.

Frequently Asked Questions

Is it normal for the Toyota check engine light to come on after an oil change?the checksthe 

The only reason why Toyota check engine light turns on after an oil change is if a sensor got disconnected by accident. Otherwise, there is no reason for a route oil change to trigger the Toyota CEL to come on.

Can I reset the Toyota check engine light by disconnecting the battery? ,,

Yes, you will reset the check engine light, but that doesn't fix the problem. If you believe the problem has been fixed, drive for a couple of days and the light will turn off on its own. Another downside of disconnecting the battery to reset Toyota check engine light is that any trouble codes that can help you diagnose the problem will be cleared from the memory.

Visitor, February 26, 2020
Very informative! Thank you for explaining everything in lay terms. The pictures were extremely helpful!!
Lonas, September 14, 2021

In my case, it was that a little antifreeze was missing from the radiator.