What is the first thing to check when the check engine light comes on?

Author: Mr. Stevie Rempel  |  Last update: Wednesday, August 27, 2025

Check your gas cap first. Many vehicles have a loose gas cap indicator that will be triggered before your check engine light comes on. If your gas cap is loose or the seal is not tight, the vapor leakage can cause your fuel system to trigger the check engine light.

What is the first thing to do if the check engine light is on?

These conditions mean you should pull over and shut off the engine as soon as you can find a safe place to do so. On some cars, a yellow check engine light means investigate the problem and a red one means stop right now. Try tightening your gas cap. This can often solve the problem.

Why is my engine light on but nothing seems wrong?

Check engine lights can turn on for a number of reasons. Some can be minor problems such as tightening the gas cap, and others can be serious problems like engine issues. If your vehicle is running fine, the check engine light may signal a minor issue, but it is best to visit a mechanic to make sure.

What is the most common cause of a check engine light?

Oxygen Sensor Malfunction

One of the most common reasons your check engine light may come on is that your oxygen sensor is failing. Your local auto repair shop in Western Washington can replace it for you quickly, which will restore your vehicle's ability to measure unburned oxygen in its exhaust system.

What is done first when the check engine light is illuminated?

What is done first when the check engine light is illuminated? First, check if the gas cap is loose or damaged. If that doesn't resolve the issue, observe the car's performance and, if needed, use a diagnostic tool to identify the cause.

The Top 5 Reasons Your Check Engine Light May Be On

What two steps should a driver take when a check engine light comes on?

1) Check your gauges – Look for an indication of low oil pressure or that your vehicle is overheating. If either of these issues are present, turn your vehicle off to prevent any further damage. 2) Inspect the condition of the battery and charging system – If you lose power from the battery, your vehicle will die.

What do mechanics do for a check engine light?

Your mechanic will plug the code reader into your vehicle, and it will instantly scan all the systems your car computer manages. If something is not firing correctly, the vehicle computer will display a code on the code reader that corresponds with a major mechanical system.

What is the most common check engine code?

The Most Frequent Diagnostic Codes for Check Engine Lights & Their Meanings
  1. Engine Misfire: P0300 to P0305. ...
  2. Emissions Issues: P0400 to P0499. ...
  3. Failed Oxygen Sensor: P0150 to P0175. ...
  4. Catalytic Converter Problems: P0420 to P0434. ...
  5. Mass Airflow Sensor Damage: P0101 to P0104 & P010A to P010D.

Does AutoZone check engine light for free?

We can help you get a reading yourself. Borrow an OBD reader to get a Check Engine Light reading with the AutoZone Free Fix Finder Service. It's a simple task that takes less than two minutes.

What is a false check engine light?

However, sometimes the check engine light will come on for no apparent reason. This is known as a false alarm. There are a number of reasons why false alarms can occur. One possibility is that the sensor that detects problems in the engine is faulty.

What does a solid check engine light mean?

Sensors activate the check engine light when internal problems arise. A steady check engine light indicates a non-emergency issue, such as a loose gas cap. Flashing check engine lights warn of severe situations requiring immediate attention. Standardized diagnostic codes help identify the trouble.

How much does Autozone charge to scan?

Most auto parts stores will run a code scan for you for free. It's worth it to them because then you will buy the sensor from them that the code indicates is the issue.

Can low oil cause a check engine light?

Low Oil and Check Engine Light

However, low oil pressure, which can be caused by low oil levels, can be a reason for the check engine light to turn on. Low oil pressure can seriously interfere with your car's performance and disable your vehicle if not addressed immediately.

Can AutoZone tell me why my check engine light is on?

Visit Your Local AutoZone Store for Free Fix Finder Service

You'll receive both a printed and digital copy of the report for your convenience. The report not only identifies the issue but also recommends solutions and appropriate parts for a repair.

What is the first thing that one should check if an engine does not start?

One thing you can do is to check the battery. If the battery is low or if there is corrosion on the terminals, the starter motor may not be able to turn the engine over. You can test the battery by using a voltmeter. Another thing you can do is to listen to the starter motor when you try to start the car.

Why is my check engine light on but my car runs fine?

The check engine light indicates something is wrong with your engine, the emissions system, or the computer that monitors those two. If there are no other symptoms, your check engine light may indicate a problem with your computer, a loose gas cap, transmission errors, or problems with your O2 sensor.

Does disconnecting battery reset codes?

Yes, if enough time has passed since disconnecting the battery. Once all residual electricity has dissipated from your car's circuits, the volatile memory in your car computer, also known as the Engine Control Unit (ECU), will be cleared, resetting it to its default settings.

Where to go when the check engine light comes on?

Once you notice your check engine light has come on, pay attention to how the car is driving. Does something feel off? If so, reroute yourself to the nearest mechanic to get the car checked out. If the car seems to be running fine, you can check a few things on your own before heading to the mechanic.

Will needing an oil change make the check engine light come on?

In conclusion, while the check engine light can be a cause for concern, it can come on for something as simple as needing an oil change.

How do I check my engine code without a scanner?

You first want to press and hold the odometer reset button and the trip button at the same time. While holding those down, turn the ignition on and release the odometer reset and trip buttons. After taking these steps, the diagnostic codes should appear in your odometer display.

What code will a bad catalytic converter cause?

A common emissions code seen in the field, a P0420 trouble code indicates that the catalytic converter isn't functioning efficiently. To work at peak efficiency, the emissions or feed gases entering the catalytic converter need to be perfectly balanced and not excessively elevated.

Is it okay to drive with the check engine light on?

If the light comes on and remains on, yet everything seems to be working like normal, you should be able to continue driving. But it is important to schedule an appointment to have the issue diagnosed and fixed. If the light comes on and it is blinking, this is an indication of something more serious.

Can I diagnose a check engine light myself?

Diagnosing your check engine light

Buy an OBD-II scan tool: There are affordable tools that allow you to run a diagnosis yourself.

Can a car throw a false code?

Bad grounds on other sensors (we know from grim experience) can trigger practically every conceivable sort of false code, since the computer has no way of telling whether the signal is off or the ground is out of range.

What is a loose gas cap?

The most common symptom of bad gas caps is a gas cap that is loose or a gas cap that won't completely tighten. This might seem insignificant, but if it's not completely sealed then the fuel system can be contaminated with dirt and grime.

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