How to diagnose Mercedes-Benz Check Engine Light (CEL) problems.
Is your check engine light on? Is it flashing? Did the check engine light come on while driving? Don’t panic.
Instructions on how to troubleshoot Check Engine Light / Check Engine light.
To complete this task you will need a simple OBD II scanner. These diagnostic scanners are a must for all car owners. Within seconds you will be able to find out why the check engine light is on. Here are some of the bestselling OBD II scanners on Amazon, several of them selling for under $15.
LocateOBD II port.
Look under the steering wheel, in the drivers footwell. Underneath the dashboard you will find the port where you plug it in your OBD II scanner. It very obvious and you can’t plug your scanner in the wrong port because it doesn’t fit elsewhere. Watch the following video if you need help with locating the OBD II port.
- Turn the key to second position. All the dash lights come on but do not start the car.
- Hit READ on the scanner. You will see codes such as P0300. Write all of them down if you have more than one. iCarsoft i980 Advanced Mercedes-Benz scanneris shown in the picture below.
- If you are having trouble with a Mercedes Benz then go to mercedesmedic.com/
faultcodes/ to get an idea of what your problem is.
- If you want to do more research then use Search function on Mercedes Medic or any other search engine to get a better idea of the problem. On any search engine enter the manufacturer and the code you got from the scanner. For example: Mercedes-Benz P0300
What should I do if Check Engine light comes on while driving?
- Make sure your engine temperature doesn’t go past the half mark. You don’t want your temperature gauge to be in the red, overheating zone.
- Keep an eye on your dash to make sure the oil light doesn’t come on. Very unlikely but if it does you are in serious trouble If your oil light comes on STOP the car right away. You would be better off towing the car home or to a mechanic in this case.
- On the luxury cars such as Mercedes Benz, BMW, Lexus, Audi; depending on the reason of the check engine light, the car may go into limp / emergency mode and transmission will no longer shift properly. Don’t panic. This is for safety reasons and to avoid further damage to your car. Once you make it home and use the OBD II scanner to get the fault codes.
Top Reasons Why your Check Engine Light is On.
- Loose fuel cap or damaged cap. If the fuel cap is not tight or not sealing properly the Check Engine light is going to come on. That’s because the car will test the fuel system to make sure it can hold pressure. If it fails this test then you will get CEL on. If you have a OBD II scanner such as the one mentioned above then you can know for sure if this is your problem.
- Oxygen Sensor O2 You car has a few oxygen sensors typically between 2 to 4. They measure the unburned oxygen. If your Check Engien Light is on because of O2 sensor you may be getting poor fuel economy as well. The input values from the O2 sensor are used to adjust the fuel delivered to the engine. You can get O2 sensors at a fraction of dealer prices on Amazon, that will fit Mercedes Benz. Check this one here for example.
- Bad Catalytic Converter If these go bad they start to get clogged. If that the case you will loose a lot of power and the car will feel sluggish specially going uphill. You are looking at $200 to $400 for an universal cat, and $600 to $1200 for exact fit.
- Mass Air Flow Sensor MAF The MAF measures the air going into the car and in some cases the temperature of air to properly adjust the fuel mixture ratio. They get dirty and malfunction. You may be able to get away with cleaning yours but a new one may be worth it. You can get one for $50 or even less on Amazon.
- Bad Spark Plugs / Wires / Spark Plug Coils Newer cars don’t use spark plug wires, instead they use spark plug coils who sit right on top of the spark plug. Either way if yo u have an older car with wires or newer one, any of these components could cause the check engine light to come on. Your Check engine light will flash on the dash. If you scan the car you will get a code such as P0300 P0301 or P030* Check these spark plugs on Amazon and read some reviews before you buy.