With the professional Car Key ECU Test Coil, it’s very easy and convenient to test EIS and key for Mercedes-Benz / BMW / Audi / VW and other vehicles.

It can be used for the following situations.

1.EIS broken

If your EIS is broken, when you insert the key, and put the Car Key ECU Test Coil (in red), the indicator of the test coil will not be on.

2.Check if EIS and key are matched and work well:

Put the car key ECU test coil on the EIS, and insert the key into the EIS, the light will be on and keep.

Connect CGDI MB Benz EIS ELV Testing Platform Instrument Emulator to the EIS by the EIS Patch Cord

Then you can check the key status

When your key is on the vehicle start status, the indicator of the test coil is off. That means the EIS and the key are all good.

Use another key to test, the coil indicator is on, after 3 or 4 seconds, the light turns off automatically. That means the key is not matched with the EIS.

3.Key problem

Put the car key ECU test coil on the EIS, then insert the key into EIS, you can check it flash.

If the light comes on and goes off immediately, or it flashes twice, that means the key is not matched the EIS, or the key is hopping code.

FYI…

These Mercedes- Benz EIS models can work with CGDI MB Benz EIS ELV Emulator and Car Key ECU Test Coil.
204             207
212 old        212 new
166             246
209             211       169
203             463
639K Line     639 CAN Line
202           208       210
215           220       230
216 old      216 new
221 old      221 new
164 old      164 new

src: https://www.cgdishop.com/wholesale/cgdi-mb-benz-eis-elv-testing-platform-instrument-emulator.html