Blog Car Care Advice 10 Common Causes for an Active Toyota Check Engine Light
Car Care Advice

10 Common Causes for an Active Toyota Check Engine Light

Looking for a mechanic near you for maintenance or repair? RepairSmith brings the shop to you. Get a free instant quote today.
Get a Quote

A Toyota Check Engine Light (CEL) can turn on for several reasons, confusing many drivers.

What exactly does the Check Engine Light mean?
And what should you do next?

Don’t worry! We have the answers to help you handle the situation and keep old or new vehicles in great shape.

This Article Contains

Let’s get rolling. 

What Causes the Toyota Check Engine Light to Turn On?

The Check Engine Light (CEL) in a Toyota Corolla or other models comes on when the Engine Control Module (ECM) identifies an emission control or engine problem. Here are nine common triggers:

1. Faulty Oxygen Sensor

The oxygen sensor or O2 sensor monitors oxygen in the exhaust gases and helps the ECU adjust the air-fuel mixture in the engine. When the O2 sensor malfunctions, it may send incorrect data to the ECM, leading to an imbalanced mixture that causes a misfire and activates the Check Engine Light. 

2. Clogged Mass Airflow Sensor

The Mass Airflow sensor (MAF) measures the air entering the engine, which is crucial for proper fuel combustion. When it gets clogged or dirty, it can’t accurately measure the airflow and can lead to incorrect fuel delivery, triggering the Check Engine Light. 

3. Catalytic Converter Problems

The catalytic converter reduces harmful emissions through chemical reactions. However, when damaged or clogged, its emissions-reducing function is compromised. If the ECM detects emissions exceeding acceptable limits, it activates the CEL.

4. Missing, Damaged, or a Loose Gas Cap 

The gas cap creates an airtight seal, ensuring fuel vapors stay within the fuel system. A damaged or loose gas cap can lead to a fuel vapor leak and reduced fuel economy, which triggers the Check Engine Light. Another frequent trigger is a missing gas cap, especially after refueling or during routine maintenance. 

Tip: Make it a habit to inspect the gas cap regularly to avoid such problems.

5. Evaporative Emission Control System (EVAP) Issues

The EVAP system is designed to capture and store harmful fuel vapors. When you drive, these stored vapors are pulled into the engine, mixed with fresh air, and then burned along with the fuel to reduce harmful emissions.

However, issues with the EVAP system, like leaks or broken parts, can mess up this process and trigger the Check Engine Light.

6. Worn Spark Plugs, Spark Plug Wires, or Ignition Coil 

Spark plugs and the ignition coil help start the engine by igniting the fuel in the cylinders. Spark plug wires carry strong electricity from the ignition coil to each spark plug. Over time, the spark plug, spark plug wires, and the ignition coil can wear out due to constant exposure to heat, dirt, and electrical stress.

This can cause engine misfires, reduce fuel economy, or cause engine stalling. You’ll notice an illuminated Check Engine Light on your dashboard in such cases.

7. Faulty Transmission 

If the transmission system fails, it could lead to a severe engine problem, like a sudden loss of engine power or difficulties shifting gears. These problems can trigger the Check Engine Light.

Tip: Regularly check the transmission for wear and tear signs, especially if you own a 2021 Toyota Highlander or a 2013-2018 Toyota RAV4.

8. Weak Battery

A weakened battery can result in an inadequate power supply to your vehicle’s electrical system, including the alternator, lights, radio, and various Toyota accessories. This situation can prompt the ECM to activate the Check Engine Light as a precautionary measure.

9. Illuminated VSC Off or Trac Off Light (Traction Control) 

The Traction Control and VSC system (Vehicle Stability Control) are advanced safety features commonly found in new vehicles manufactured by Toyota. 

When the VSC Off or Trac Off Light activates, it means your vehicle has turned off these features. An illuminated Trac Off or VSC light is typically accompanied by engine problems, which can also trigger the CEL.

10. Engine Control Module (ECM) Malfunctioning 

The Engine Control Module (ECM) controls and optimizes the engine’s operation for performance, fuel efficiency, and emissions. Malfunctions in this communication can lead to Check Engine Light activation.

Now, the Check Engine Light can appear in various patterns. We’ll discuss what these mean.

How to Assess the Check Engine Light’s Severity in a Toyota

Whether you’re driving a Toyota Camry or a Toyota Crown, three scenarios can indicate the severity of a lit CEL:

1. Intermittent Check Engine Light

If your CEL intermittently turns on and affects performance, it’s best to minimize driving and call a mechanic (or visit a Toyota service center). Ignoring it could potentially leave you stranded.

2. Steady Check Engine Light 

A steady amber-colored or yellow light is important but not critical. Typically, the yellow light turns on to indicate that a system is about to fail or a service like an oil change is due. To determine the exact cause, call a Toyota certified mechanic.

Tip: With the Toyota app, you can receive updates on engine performance, CEL events, safety recalls, and service specials.

3. Flashing Check Engine Light

A flashing Check Engine Light signifies a severe engine problem. Pull over ASAP and arrange for your vehicle to be towed to a mechanic or service center. Continuing to drive with a flashing CEL may result in irreversible engine damage. 

To determine the actual cause of a steady or flashing light, you need a proper diagnosis of the registered Check Engine Light codes. Coming up next are the costs associated with it. 

How Much Does a Toyota Check Engine Light Diagnosis Cost?

The average diagnosis costs range from $80 to $150 (excluding taxes and extra fees) for most prominent Toyota models like:

However, the final cost of diagnosing your Toyota’s check engine warning light can depend on the parts needed, labor charges, and your state.

You can buy Toyota certified parts at the following estimated prices:

The CEL should turn off once the underlying issue is diagnosed and fixed. But if it doesn’t, let’s review how to reset the illuminated Check Engine Light.

How to Reset the Check Engine Light in Your Toyota

Warning: If you clear the warning light but ignore the underlying Check Engine Light codes, you risk aggravating the issue.

Here’s how a Toyota service mechanic would reset the CEL:

  1. The mechanic will park the vehicle in a safe location and turn off the engine. 

  2. They’ll locate the negative battery terminal and loosen the cable’s nut. They’ll remove the negative cable from the battery terminal and leave the cable disconnected for at least 30 to 60 seconds.

  3. Next, they’ll reattach the negative battery cable and tighten the nut.

  4. Finally, the mechanic will start the engine and observe whether the Check Engine Light is off. If it remains off, the CEL has been successfully reset.

Wrapping Up

The Check Engine Light warns of possible car problems, so it’s wise to consult a Toyota certified mechanic immediately. This prevents further issues and costly repairs down the road. But since it’s best not to drive with a Check Engine Light, think about how convenient it would be to have the expert mechanics from RepairSmith come to your doorstep.

We’re a dependable mobile vehicle repair service available every day of the week. Our skilled technicians can handle all repairs, which come with a 12,000 miles | 12-month warranty.

Get a quote for a Check Engine Light diagnosis or any other service!