How to Respond When the Car Malfunction Lamp Indicator!

A vehicle Malfunction Lamp Indicator or Malfunction Indicator Light (MIL) alerts the driver when the electrical system detects probable engine, transmission, or emission problems. But what triggers the this Lamp Indicator?

Technically, there can be several reasons. Anything as simple as a loose or worn gas cap to major issues like MAF/oxygen sensor failure, a defective catalytic converter, or something else can force the ML Indicator to illuminate.

How to Respond When the Car Malfunction Lamp Indicator!

What Does the Malfunction Lamp Indicator Signal?

It is a little yellow light in the shape of an engine designed on the vehicle dashboard. Also known as the Check Engine Light (CEL), it signals a condition that could lead to excessive emission/pollution.

In most cases, the ML Indicator illuminates briefly while you crank the engine to start your car, but it is expected to turn off automatically after the engine is turned on.

However, if the indicator stays on or flashes in between driving, it signals one of the following problems:

  1. Blinking or flashing occasionally indicates temporary engine malfunctions caused by defective components such as a spark plug, ignition coil, or internal battery.
  2. A solid steady light indicates leaving the gas cap off when you last filled it up or some other defects restricting or affecting your vehicle’s emissions system.
  3. Constant flashing is the most serious type of sign that your vehicle’s engine is misfiring due to either catalytic converter failure or damaged sensors.

7 Reasons Why Car Malfunction Lamp Indicator Lights Up:

Here are the seven most common causes why the MIL must be coming on:

1. Loose Gas Cap, Failing Battery, or Ignition Coil Failure: 

When the gas cap is not properly tightened, it can cause a leak or a pressure drop to trigger the car malfunction indicator. 

Your vehicle’s computer needs a steady supply of power to function properly. But if the internal battery is weak or fails to provide enough voltage, it will disrupt and trigger the ML indicator.

The ignition coil generates the spark that ignites the fuel in your car’s engine. If it fails, it can cause a misfire or a power outage, triggering the indication lamp.

2. Excess Consumption, Smoke Emission, or Abnormal Operating Temperature: 

Generally, the Malfunction Lamp comes on while driving, when your vehicle engine is no longer running like usual due to the following issues:

  • Detected excessive fuel or oil consumption, 
  • Combustion failure causes excess smoke emission, or 
  • Engine cooling system defect/failure causing a very high operating temperature.

3. Problematic Fuel Supply or Defective Supercharger:

If your car has a fuel supply or delivery system problem, such as a dirty fuel injector or pump, this will cause a loss of power and a jerk when accelerating to trigger the MIL.

You may also notice the malfunction indicator if the supercharger suddenly stops working correctly due to improper cooling or defective parts like the turbo compressor.

4. Deteriorated Glow Plugs or Electrical Errors: 

The cylinders of diesel engine cars need to achieve a specified temperature before they can be started. 

But gradually the cylinder glow plugs declines and fail to reach that level.

Internal electrical connection errors, such as loose or worn wiring connections or a faulty spark plug that fails to generate enough spark may force the system to turn on the indicator.

5. Failed Mass Airflow or Oxygen Sensor: 

The mass airflow (MAF) sensor regulates and calibrates how much air enters the engine cylinders. It enables the system to provide the precise amount of fuel needed at any given time.

But a damaged MAF sensor causes a major drop in the engine’s performance.

Similarly, the Oxygen sensor oversees sensing the fuel or gas in the exhaust and allocating the right fuel amount for burning. 

But a prematurely failed Oxygen sensor makes the engine suffer from improper combustion.

6. Failed EGR Valve: 

EGR valve is the main component of the vehicle Exhaust Gas Recirculation system and is in charge of recycling exhaust gases in combustion to prevent emission

So, if this valve malfunctions, the engine’s consumption, and power will increase.

7. Faulty Catalytic Converter: 

The catalytic converter is in charge of preventing dangerous emissions into the atmosphere. 

Overuse/aggressive use, or accidental blow can damage the catalytic converter, causing engine performance to suffer as well as strange noises and vibrations while driving.

What to Do When the Car Malfunction Lamp Indicator Lights Up?

Once you notice that the Malfunction indicator is flashing, do not panic and follow the step-by-step instructions:


Pull over your car in a safe place and turn off the engine. Then, if you already have an OBDII code scanner installed, look for a specific code reading and check your car’s manual to follow the instructions.


If you do not have the OBDII code scanner on your vehicle, there’re two ways:

  • Perform a fast self-inspection on your car to identify and repair the main problem, or  
  • Use an OBDII code scanner to identify the specific error code to troubleshoot the issue.

If you plan to run a self-inspection, try to turn your car engine on and off three times to reset the indicator. Wait for a moment before starting the ignition. Again, turn the engine off for a second. 

Now drive your car for a while after doing this procedure twice to test if the MIL turns off automatically or remains on.


Check whether the engine is starving for fuel or oil and add them if needed. Drain out the stale fuel and pour fresh gasoline. Inspect whether the gas cap is worn or loose and tighten or replace the gas cap if needed.

Then, reset the Malfunction indicator by disconnecting and reconnecting the internal battery:

  • Open the hood to take the battery’s positive power cable off.
  • Use a wrench to remove the battery for a minimum of fifteen minutes.
  • Then, perform three full engine starts to erase the Emission data from your car’s memory.
  • Reattach the positive power wire to the battery and reinstall the battery correctly before turning the ignition key. 


Check the ignition coil, fuel pump, and injectors for any issues. Replace them if necessary. 

Examine the spark plug, valve seals, head gaskets, and piston rings. Service them as required.

Inspect the MAF and Oxygen sensors to see if any of them have dropped. Replace the one who declined.

Make sure to examine the catalytic converter and replace it if necessary. Also, clean or replace the EGR valve if needed.


If the above self-conducting test feels too troublesome, get an OBDII scanner with Autel MP808TS and follow these instructions:

  1. Locate the OBD port on your car and connect the scan tool correctly.
  2. Press the enter menu so that the OBD scanner may connect to and run the ECU.
  3. Once the diagnostics are done, the trouble codes will be displayed on the OBD reader’s interface and you will find the details of those trouble codes on your instruction manual.
  4. Or clear the error codes with the OBDII scanner tool. Just press “Delete”, then press “Clear”, or “Reset”, and it’s done.

How Much Does It Cost to Turn Off the Malfunction Lamp Indicator?

Do it free of cost by clearing the error codes or switching the engine on and off 3 times. Besides that, the actual cost will depend on your car type or model, the number of damaged parts, and the replacement cost

Here are some possible replacement estimates:

Repairing/Replacing PartsEstimated Cost 
Gas cap($25 – $75)
Oxygen sensor($150 – $450)
Spark plug($100 – $250)
Ignition coil($150 – $450)
Fuel injector($300 – $750)
Mass Airflow sensor($250 – $450)

Can I Drive My Car with the Malfunction Lamp Indicator?

Initially, one may drive their vehicle for up to 100 miles. But it is not advised since the indicator might be a sign that your engine is misfiring or something more serious that needs to take care of

Thus, stop your vehicle immediately as soon as you notice the indicator and check.

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