Understanding Toyota Check Engine Light
Although Toyota vehicles are very reliable and durable, even a Toyota can suffer from breakdowns and check engine problems.
If there is an engine or emissions related problem, your Toyota will turn on the Check Engine light on the dashboard. You might also get other warnings such as VSC and Trac Off coming on.
In this guide, you will learn about common problems that trigger Toyota check engine light to come on. In addition, you will find step by step instructions on how to read and clear Toyota check engine light using an OBD2 scanner.
The first thing that happens, is that your Toyota check engine light stays always on. Other common symptoms that you may notice include:
Engine runs rough
Traction Light or VSC Light come 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 prevent any additional damage, start looking for a good place to safely pull over and turn the engine off and check a few basic items as outlined below.
In some cases, 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.
Toyota check engine light can come on for many reasons starting to a loose gas cap, to a bad ignition coil or spark plug and even due to a blown head gasket. Let's take a look at common problems that trigger the check engine light on a Toyota.
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.
Many Toyota owners don't realize that spark plugs are maintenance items.
Most Toyota vehicles require the 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 to cause the check engine light to come on. In addition, you will most likely get engine misfire where the engine starts to shake.
Idle Air Control System
If you have an older Toyota with a cable operated throttle you might have problems with 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
Vehicle speed sensor failure
Although generally very reliable, Toyota is well known for a vehicle speed sensor failure.
This will trigger a check engine light, combined with an 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 a code P0500.
Crankshaft position sensor
If you are experiencing sporadic ‘crank without a start’ situations, 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.
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 get chain overstretching 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 timing chain has never been replaced.
Mass Air Flow Sensor
If you are experiencing rough idle, lack of power or hesitation on accelerations, it is likely that your engine is running lean. Most Toyota engines have mass air flow 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.
Oxygen Sensor / Catalytic Converter
A ‘check engine’ light caused by an 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 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. Codes: P0420 to P0431.
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 to 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.
Variable valve timing
Most Toyota engines have a variable valve timing (VVT). Aforementioned oil sludging, as well as 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.
What to do when Toyota check engine light turns on?
Check Gas Cap
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 be used to reset Toyota check engine light as long as there are no other issues present.
Allow the engine to cool down. Next, check the engine oil level and the coolant level on the overflow reservoir. You may continue your journey if you don't notice any performance issues and the check engine light is not flashing.
Read Diagnostic Trouble Codes (DTC)
Read the codes with an OBD2 scanner via the diagnostic port under the dashboard. See instructions on the next section.
How to diagnose Toyota check engine light
- Locate the OBD2 port under the dashboard.
- Plug in your OBD2 scanner. Turn on the ignition but do not start the engine.
- Turn on the scanner and let it communicate with the car. Select Read Codes from the main menu.
- 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.
Check Engine 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 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 to drive your Toyota if the check engine light is blinking.
Frequently Asked Questions
Toyota VSC and Check Engine Lights 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. In addition, traction control or Trac Off light may come on as well.
- If that is the case, it doesn't necessarily mean that there is 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
- It is common for the traction control light to come on when the check engine light on your Toyota comes on. The traction control gets disabled but that doesn't mean that there is a problem with Trac system. Just fix the check engine light problem and your Trac Off light will reset as well.
Is it normal for Toyota check engine light to come on after an oil change?
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 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.
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