In this guide, we take a look at common problems that turn on BMW Check Engine Light (CEL) also known as Service Engine Soon (SES).
What does BMW Check Engine Light mean?
If your BMW check engine light (or service engine soon light) stays on it means that the Onboard Diagnostic System (also known as Digital Motor Electronics DME) has detected a problem with the emission system, engine, or transmission. BMW check engine light may come on due to something as simple as a loose gas cap but it can also be an indication of an expensive engine or transmission problem.
It doesn't mean your BMW needs to be towed unless the car is overheating or if the check engine light is flashing. Continuing to drive if your BMW check engine light continues to flash can lead to more serious and costly problems down the road.
There are hundreds of problems that may trigger the check engine or service engine soon in a BMW. BMW specific problems include:
- Cracked or loose hoses
- Old battery
- Bad mass airflow sensor,
- Low fuel level,
- Bad charcoal carbon canister,
- Wire harness,
- High-Pressure Fuel Pump (HPFP) failure,
- Crankshaft sensor bad
- Injectors (when applicable).
Do not start replacing BMW parts without reading the fault codes.
If you don't have a BMW scan tool, have a shop that specializes in BMWs read the codes and troubleshoot the problem for you. Your local auto parts store may read your BMW check engine light free of charge.
Once you have a diagnosis performed, you can decide if the repair is something that you can tackle yourself or let a BMW shop complete the work.
What to do when BMW check engine light turns on?
The first step is to check the fuel cap. If the cap is loose it will trigger the CEL. Tighten it until you hear it click.
Most 2005 and newer BMWs will also show a separate symbol to remind you if you forget to tighten the fuel cap. If the gas cap was loose and you tighten it. The CEL light will reset itself in a few driving cycles, typically within a day or two.
If the BMW drives fine, closely monitor the engine temperature. If your BMW is overheating or oil light is on, stop driving your BMW immediately. Get the BMW towed if necessary.
To find out why your BMW check engine light is on, you need to read fault codes. This is a simple procedure you can perform yourself.
How to diagnose BMW check engine light
These instructions show you how to read and clear codes related to check engine light on a BMW. It is preferred to diagnose BMW check engine light with an OBD-II scanner that can read BMW specific fault codes such as Foxwell NT510 for BMW.
- Locate the diagnostic port on your BMW. The port is under the dash on the driver's side.
- Plug scanner into the OBD2 port. Turn on ignition by pressing the start button without pressing on the brake pedal.
- Allow the scanner to turn on.
- Press read/enter to read codes from DME Module.
- Write down the codes and clear them once you are completed.
This procedure only allows you to read and clear codes from the ECU / DME / DDE.
If you have other problems a generic OBD2 scanner will not be able to read and clear the codes. In other words, a generic OBD2 scanner is only able to read and clear codes from the ECU but not form other modules including ABS, SRS, Airbag, DSC, Stability Control, EGS Transmission, etc.
Note that you can read the codes, but you can't clear them unless you fix the problem that triggered the code. If you don't fix the underlying problem the light and the code will return. In some cases, it returns right away, in other cases it can take a day or two.
BMW Check Engine Light Symbols
There is a difference between BMW Check Engine Light vs. Service Engine Soon
BMW Check Engine Light Flashing
If the check engine light is flashing, generally means that the DME module has detected a misfire. If the light is flashing you will notice poor acceleration, BMW engine shaking.
This problem is often caused by bad spark plugs or bad ignition coil which is a common problem with many BMWs including 1, 3, 5, 6, X1, X3, X5 series.
Other possibilities include a vacuum leak, bad mass airflow sensor, clogged catalytic converter, and a blown head gasket. It is not recommended to drive a BMW if the service engine light is flashing.
When the BMW 'service engine soon' light is flashing and the car is shaking you have a problem that needs to be addressed as soon as possible.
Under these conditions, your BMW will be very sluggish and the motor will shake at idle.
If the check engine light or service engine soon stay on, your BMW may drive fine if the trigger is due to EVAP related fault code.
Unless the problem is more serious in which case you may notice performance issues such as:
- BMW engine misfire
- BMW won't accelerate
- Stuck in limp mode
- Engine shakes at idle
- BMW engine overheats
- Poor acceleration
- Erratic idle
- Hard to start
BMW Service Engine Soon light may be on without any noticeable performance issues.