Troubleshooting BMW Check Engine Light & Service Engine Soon

In this guide, we 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 indicate an expensive engine or transmission problem.

Don't panic!

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.

Symptoms

Common Causes

There are hundreds of problems that may trigger the check engine or service engine soon in a BMW. BMW specific problems include:

• VANOS
• Cracked or loose hoses
• Old battery
• Bad mass air flow 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 specializing 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.

If the BMW drives fine, closely monitor the engine temperature.  If your BMW is overheating or the 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. 

Procedure

1. Locate the diagnostic port on your BMW. The port is under the dash on the driver's side. 
2. Plug scanner into the OBD2 port. Turn on the ignition by pressing the start button without pressing on the brake pedal.
3. Allow the scanner to turn on.
4. Press read/enter to read codes from DME Module.
5. Please 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 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 from other modules, including ABS, SRS, Airbag, DSC, Stability Control, EGS Transmission, etc.

BMW Check Engine Light Symbol

There is a difference between BMW Check Engine Light vs. Service Engine Soon.

	Check Engine Light - Yellow CEL Engine Block Symbol in Dashboard The problem is often minor such as a loose gas cap. Often BMW drives fine.
	Service Engine Soon - SES Light SES light doesn't always mean there is a major engine problem. BMW may run and drive fine. Don't ignore this light. Read BMW fault codes.
	Check Engine Light - Half Yellow This problem is more severe. The car usually goes into limp mode to prevent further damage. Serious engine or transmission problem BMW may be stuck in gear, Limp Home Mode

BMW Check Engine Light Flashing On and Off

If the check engine light is flashing, it 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, a common problem with many BMWs, including 1, 3, 5, 6, X1, X3, and 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 BMW's 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.