Why is my BMW engine light on?

In this blog, we will answer the question “why is my BMW engine light on’” and discuss topics related to what the research says, like what engine light refers to? what are the general issues associated with the engine light being switched on? and about troubleshooting methods.

Why is my BMW engine light on? 

A check engine light is formulated to monitor the engine and detect if there is any fault with the vehicle or engine’s systems. When the check engine light illuminates on a BMW’s dashboard, it means that there is an issue related to inappropriate air-fuel mixture flowing through the engine. This occurrence can be a problem with the intake, exhaust, ignition, or any other part that monitors the four strokes in the engine.

 How does a check engine light get illuminated in a BMW vehicle?

BMW vehicles are designed with a sophisticated monitoring control system (equipped with a computer) and plenty of sensors that are strategically placed on specific areas of the vehicle. These sensors help the vehicle by providing continuous information to the engine control unit (ECU).

If any malfunction is detected, the sensors send information to the ECU specifying that there is an issue with the vehicle’s operating conditions or that the sensor is not functioning, then the ECU illuminates the engine light on the vehicle’s dashboard 

What are diagnostic trouble codes in a BMW vehicle and How can they be accessed?

There can be several issues due to which a BMW engine light can be switched on. All issues are stored as diagnostic trouble codes in the engine management system or the onboard diagnostic system(OBD). These codes can be accessed by the driver with the help of an OBD tool. 

The tool can be connected to a port in a BMW, located below the driver’s dashboard. Subsequently, the OBD tool will display all the troubleshooting codes and issues related to the vehicle. Thus, The driver or the technician will get direct information about the issues related to why the BMW check engine light had been illuminated.

What are the most common diagnostic issues that illuminate the check engine light in a BMW vehicle?

The issues listed below are the most common reasons due to which a check engine light can get switched on a BMW vehicle.

  • Faulty MAF sensor
  • Defective O2 Sensor
  • Loose Gas Cap
  • Malfunctioning Catalytic Converter
  • Aged Battery
  • Vacuum leaks

Faulty MAF sensor

The MAF sensor measures the total amount of airflow in the engine and passes this information on to the ECU. This process helps the ECU to determine how much fuel must enter the engine. If the MAF sensor is damaged, it can’t calculate the appropriate amount of airflow within the engine, thus a misfire or rough idle can take place in a vehicle with a faulty MAF sensor illuminating the check engine light on the vehicle’s dashboard.

Defective o2 Sensor

 O2 sensor in a BMW vehicle like any other vehicle is used for measuring the amount of oxygen flowing out of the exhaust manifold and transmits that message to the ECU to vary the air-fuel ratio to its optimum condition. An oxygen sensor is fitted before and after the catalytic converter. If an oxygen sensor is defective, similar to an issue with a MAF sensor, the engine will run in a rich condition ( fuel > air) which will then reduce fuel economy, induce rough idle and cause the engine to misfire, then illuminating the check engine light on the vehicle’s dashboard.

 Loose gas cap

 The gas cap in a BMW vehicle is utilized for multiple tasks as listed below:

  • When the vehicle is idling, the gas cap prevents the vehicle from releasing gas fumes. 
  • The gas cap covers the fuel system and maintains pressure inside the fuel tank.

 So, when the gas cap is worn out or has a broken seal, fuel is evaporated, resulting in low mileage. So when the check engine illuminates right after fuel is filled in the vehicle, it is imperative to ensure that the cap isn’t loose or not lost. 

Dead Battery

Whenever the battery is low or dead in a BMW, as known to everyone, won’t be able to ignite and propel forward, or use the infotainment system and other electrical accessories. Any issue with a dead battery can illuminate a check engine light on the vehicle.

Failing Catalytic Converter

The catalytic converter is one of the major components of the exhaust system. It is normally used to convert harmful gases such as carbon monoxide (CO), Hydrocarbons (HC), and Nitric Oxides (NOx) with the help of platinum, palladium, and rhodium to reduced versions/ less harmful emissions for protecting the external environment from pollution. In a BMW vehicle, it is common for a CAT converter to fail if aftermarket parts are fitted on the vehicle. A failing catalytic converter can lead to the following:

  • Decrease the fuel mileage.
  • Increase the harmful emissions exerted out of the vehicle. 
  • Cause issues in accelerating and decelerating the vehicle.
  • Failure in the emissions test.

 All these issues stated above can trigger the check engine light in the vehicle.

Vacuum leak

BMW has a vacuum system performing tasks in various parts such as the brake booster, EGR valve system, HVAC system, etc. Vacuum leaks in a vehicle cause the following problems:

  • The vehicle runs at High RPMs.
  • Unmetered air entering the engine can cause the vehicle to run leaner ( air>fuel), thus reducing the performance of the vehicle significantly
  • The car will surge and rough idling can occur quite frequently.

Whenever any of the above-mentioned issues start happening, the vehicle will definitely illuminate the check engine light on its dashboard.

Why does a BMW vehicle falsely illuminate the check engine light? 

A BMW vehicle can falsely trigger a check engine light since the vehicle is attached with a plethora of sensors, if any of the sensors cannot communicate with the ECU or if the ECU has to be reset after an ongoing issue with the engine had been resolved, then the light can get illuminated by the ECU in the vehicle. 

This problem can be resolved by the following steps

  • Switch off the engine and put on the safety equipment.
  • Remove the negative terminal slowly ( can be found on the battery with – sign ) with a wrench and leave it aside for sometime
  • Attach the negative terminal on the battery and drive the vehicle for some distance. 

After the drive, typically, the engine light gets turned off. If the engine light is still switched on, it is best advised to visit the nearby technicians. In addition, It is important to note that engine oil warning lights and service lights are totally different from check engine lights. 

Other articles about  BMW you may be interested in

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BMW Suspension Issues Explained


In this blog, we have addressed the question “why is my BMW engine light on”, We determined that a check engine light gets illuminated due to several issues and we have outlined the common issues which majorly are Faulty O2 and MAF sensors. These issues cause the engine to misfire, surge, or rough idle. Further, the article outlines each issue in brief and also provides the user additional information on how to diagnose codes and reset false alarms.