BMW check engine light What is the reason?

BMW check engine light What is the reason?

Engine fault light elimination steps

BMW engine fault light lighting must be paid attention to because it involves a lot of parts, causing engine fault lights to light up sensors, maintenance problems, oil problems, air intake problems, mixture combustion and other problems. As the heart of the car, the impact of engine failure lights is greater or less. because there may also be false alarm failures caused by signal errors. Although there is a certain probability of false failure, in order to ensure the safety of the car as well as the possibility of small lesions and major diseases, it will cause more serious damage to the vehicle. Therefore, the owner should check the engine fault light as soon as possible, and the engine fault light can be eliminated after replacing the problem parts.

Engine fault light is a problem that every car owner encounters on a regular basis and cannot ignore because it is directly related to engine service life and driving safety, so understanding the cause is essential. Furthermore, many owners panic when they encounter this problem and do not know how to proceed. For example, if the engine fault light is lit while driving, I don't know if I can continue to drive. I hope the following introduction will give you some help.

The cause of the engine failure light

Engine fault lights are generally electrical faults, mostly involving various sensors and wiring harness faults. The DME module controls the BMW engine fault signal, and the DME is the engine's brain, controlling all electronic components, so there will be many reasons for the engine fault light to illuminate air intake, fuel supply, ignition, timing, exhaust, vacuum, and other systems in a sensor problem. A loose wiring harness connector may cause this light to illuminate. Therefore, to repair this fault, you should try to cooperate with the fault code, which makes it easy to narrow the scope of the fault and solve the problem faster.

Engine fault lights are divided into two types: red and yellow.

Under normal circumstances, when the yellow fault light is on, it means that this fault does not affect the normal operation of the engine but only reminds you that you need to find the right time for maintenance and detection to find the problem.

If the red light is on, it means that the engine failure is already very serious, and the car can no longer continue to drive. It should urgently find a safe place to stop, waiting for rescue.

So how to eliminate the yellow engine light?

  1. If the yellow fault light on the engine is on, there are some cases where it will be automatically eliminated. As for why it will be automatically eliminated, there are many reasons, but do not test and maintain because it is automatically eliminated, or you need to detect and find out the reason for the fault light!
  2. Power off the BMW, power off the battery for a few seconds, and then reconnect. In some cases, the fault light will go out. If it is still on, then you need to go to the repair shop for maintenance and find the reason.
  3. The third is the most reliable way to go to the maintenance point for inspection because the fault light is the signal transmitted by the car computer, and the problem of more than 10,000 parts of the whole car can only be checked through the BMW special inspection computer! The most correct way is to go to the garage for an inspection.

What causes BMW to turn light yellow?

The combustion state of the engine is not good.

This is the main cause of the fault light, and most of the faults are caused by this reason. A sensor is installed on the exhaust device of the engine to detect the tail

In the case of gas emissions, if the combustion state of the engine is not good, it will cause changes in exhaust emissions, causing system alarms.

The fuel quality is not good.

This reason is easy to identify and generally occurs just after refueling or after refueling and driving for a distance. Some gas stations provide fuel that does not meet the specifications for oil.

Poor product quality or the occurrence of different types of oil mixing will also cause system alarm.

The engine cylinder has carbon deposits.

After the engine is used for a period of time, some carbon deposits will inevitably accumulate inside, and if you usually use non-compliant gasoline, it will aggravate the generation and accumulation of carbon deposits. produce

Excessive carbon deposits will accumulate, resulting in disorderly ignition of the engine, engine knocking, and system alarms.

Here are some common reasons to check when you don't know how to start:

  1. air intake-related: air intake leakage, electronic throttle, air flow meter, intake pressure sensor, electronic valve servo motor, eccentric shaft motor, eccentric shaft sensor, front oxygen sensor.
  2. Oil supply related: poor fuel quality, high-pressure oil pump, fuel injector, carbon tank solenoid valve.
  3. Ignition related: ignition coil, spark plug.
  4. Exhaust-related: rear oxygen sensor, three-way catalytic converter, exhaust camshaft and bearing.
  5. Supercharging-related: intake and booster pipeline, electropneumatic pressure converter (EPDW), turbocharger.
  6. Others: crankshaft oil seal, crankshaft sensor, water temperature sensor, electronic thermostat, oil level sensor.


Damaged sensors, poor contact, or interrupted signals cause the car's ECU to receive incorrect engine data and finally misjudge the engine fault light. I believe that everyone is no stranger to sensors, such as water temperature, crankshaft position, air flow, intake air temperature, oxygen sensor, and other common sensors. The engine fault light caused by the sensor is lit, and the engine fault light generally only needs to be replaced or adjusted to eliminate the engine fault light.


Engine oil refers to engine oil and fuel for which the engine needs oil or fuel that meets its conditions to function properly. Although the unqualified oil can support the engine operation, the engine is uncomfortable to run, so the wear will be accelerated, and it will also cause the engine fault light to light up.

Mixed gas combustion

Spark plug failure, ignition coil failure, fuel pump failure, oil circuit blockage, and other problems can lead to poor combustion of the mixture. The consequence of poor combustion of the mixture is carbon deposits or knocking, which causes the engine fault lamp to light up. Measures such as replacing spark plugs, cleaning the oil circuit, and cleaning carbon deposits have a certain chance of eliminating faulty lamps.

Note: This is only a list of common fault parts that cause the engine fault light to turn on during the maintenance process, and there are many other reasons. Please add in the message. In actual maintenance, with the fault code combined with the above summary, the components related to the fault code and their related wiring harnesses should be able to find the real fault point relatively quickly.