If your Mercedes-Benz W203 C200K manufactured between 2001-2003, here i will recommend a cheapest and easiest way to read and clear trouble codes. You will like it, just read the article below:
W203 had a OBD-II port which allows you access to its Engine Control Unit (ECU) like monitors, RPMs, sensors, emission, mileage speed and an array of other parameters. When there is a problem with the car, the ECU triggers a Diagnostic Trouble Code (DTC) or Fault Code by illuminating the Service Engine / Check engine on your instrument cluster. In this situation, You can use a device such as ELM327 OBDII Scanner Adapter as a Check Engine Light DTCs Reader which works on iOS system or Android system.
To solve the problem, below is what you need to do.
Turn your iOS iPhone iPad or Android phone into a basic car diagnostic scanner!
How to connect the Bluetooth Adapter to the OBD II port and your mobile phone?
1. Find the OBD-II port on your car.
2. Plug in the Bluetooth adapter into the OBD II port. Make sure that the lights turn on in your Bluetooth adapter.
3. Pair your phone with the adapter. Go to your phones settings, turn on Bluetooth. Then search for Bluetooth devices. You will see an OBD II device discovered. Click on it and you should input a pairing code. Try 1234 or 0000. If these two codes don’t work, read the manual for the Bluetooth adapter to find out what code is.
4. Go to the App Store and download a free OBD II app that will allow you to pair with your OBDII Bluetooth diagnostic scanner. Here we would recommend you try Torque App.
5. Download and open up your App and make sure it is connected to the Bluetooth adapter. You will be able to read live engine data such as RPMs, temperature, engine load and more. More importantly, you can troubleshoot Fault Codes and retrieve the trouble codes for you Mercedes-Benz.
6. Once you see the list of error codes, click on the Menu button and hit Clear / Erase Fault Codes. Please note that you should only delete the fault codes if the problem has been repaired. If you erase the fault codes without fixing the problem, the check engine light will turn on again. Depending on what triggered the check engine light initially, it may turn on right away or it could take a few days to come.
Benefits of using ELM327 Bluetooth to check the engine light:
ELM327 Bluetooth adapters are great as not only can read and erase the service engine light, but they also can be used to stream real-time information. Elm327 Bluetooth adapter paired with Torque app can provide valuable information such as:
Stream Realtime Information
Check / Read Fault Codes DTC
See Test Results
Display a tachometer or accelerometer
Record your 0-60 or 0-100 mph times.
Fuel Flow Rates
Temperature of coolant, oil or intake air
Depending on the adapter that you use you may be able also to store profiles, get fuel economy readings, and horsepower.
Using this ELM327 OBD2 Bluetooth Adapter as a scan tool is the cheapest way to troubleshoot your Mercedes-Benz W203 C200K . Not only will you be able to read and erase the fault codes (diagnostic trouble code), but you can use your phone to see if you are driving efficiently and check if you are ready for the emissions test via your iOS or Android Phones.
Other Bluetooth scanners that are highly rated work with most car models without problems you can find at obdii365.com.
Note that these cheap Bluetooth OBDII scanners only read and erase the check engine light. If you need to read and clear codes from other control units such as ABS, SRS, ETS, TCU, you need to pay more for a professional scanner such as XTUNER E3, XTUNER X500 etc.