TAR

Yesterday I received the most unwelcomed (and unexpected) diagnosis that my EIS would need to be replaced on my '05 CLK cabrio. The car has been the most reliable and enjoyable Benz I have owned, so this development was a disappointment, for sure. What I would like to better understand is what causes the EIS to become problematic.

Background: My car was asymptomatic until driving on Wednesday when I suddenly loss climate control, window function, turn signals, use of all dash function, and the auxiliary radiator fan ran constantly. I had never experienced any reason to believe that a problem was looming prior to the symptoms being manifested on Wednesday. Got the car to the dealership where the cause was identified, and I received the bad news yesterday.

Aside from the cost of repairs, I have a need to better understand EIS. I have a basic understanding of its purpose. I do not understand what causes it to fail.

TIA.

bbirdwell

Read this for description. Repair company but out of the USA.
http://www.ogsmechanics.com/tutorial...er-key-module/

Rudeney

The EIZ (also called EZS) is sort of the master control unit for the CAN bus. The CAN bus is like a computer network that runs throughout the car, much like an Ethernet cable network in your home or office. I allows the devices in your car to communicate with any other device in your car each of thee devices being separately wired to one another. \

For example, on your driver's door, you have buttons for all the windows, the seat controls, memory, a power mirror, lights, and locks. Add in KeylessGO and you have a door handle sensor, lock button, and antenna. In other words, that door is full of electronics. But each of those does not connect to its own wire coming out of the door. Instead, there is a door controller, basically a computer, in the door that all of those connect to. The controller connects to the car's CAN bus with two wires. When you press one of the seat buttons, the door control sends a signal across the CAN bus. All devices "hear" it, but only the seat controller "listens" and operates the appropriate motor.

Multiply this against all the different buttons and functions all over the car and you can see that the CAN bus is a very busy network. Not only that, there are two CANs - one for the engine and drive authorization systems, and another for "consumers" liek the interior luxury features (power/heated seats, lights, etc.). The EIS is the "router" that allows the cabin CAN bus to send signals to the engine CAN bus and vice-versa. For example, the ACC (climate control) has to deal with internal controls and the ventilation fan (cabin CAN) but also it needs to tell the ECU to spin up the engine suction fan and activate the compressor (engine CAN).

Symptoms of a bad EIS are often starting (drive authorization) issues, but also, if the two CANs can't communicate, then that's usually the EIS at fault. As that linked article mentions, it uses a Motorola CPU that can fail, but also, I think the CAN connections to the circuit board can fail. This may be reparable by someone with good electronics skills, but, the sure-fire solution is to replace it with a factory-fresh part with dealer coding.

TAR

Thank you for your explanations. I have a much better appreciation of the EIS now than prior to reading your responses. Picking the car up this morning from the dealership. Hope it all goes well!