What is the Mercedes Benz DAS / Star
Most automobile manufacturers have their own diagnostic tool to query and report faults codes for their branded cars. The MB diagnostic system is known as Star Diagnosis System or SDS (often shortened to just Star). There are other names and acronyms associated with the system:
DAS Diagnosis Assistance System
Xentry Xentry (it is not an acronym)
Originally, the MB diagnostic tool was call HHT (Hand Held Terminal) to work on cars produced between the late 1980s and the early 2000s. By todays standards, it was a very basic and somewhat unsophisticated tool.
The next generation of diagnostic tools from MB was DAS. It came out in the early 2000s to better handle the growing number of controllers used in current cars. This system is the primarily focus of this article. DAS was a significant advancement over the HHT. DAS can talk with each controller within the car, read sensor data, control functions (ie: raising or lower windows, turn on headlights, etc.), and report real time operating data such as from the running engine. Additionally, DAS is required when a controller is replaced to add the necessary coding to the controller so that it matches the car, or to update the coding when retrofits / changes have been carried out.
The next and most current generation of MB diagnostic tool, Xentry, is for cars produced from about 2005 (varies with model) the R171 uses Xentry.
For some MB models produced during the early 2000s, portions of the car are diagnosed using HHT and other portions DAS for us, this means the R170.
As cars have become more sophisticated and expanded in the number of onboard control modules (each controller is a micro-computer with all controllers interconnected through multiple wired networks within the car), the diagnostic tools used to interface with cars have had to also become more sophisticated. Additionally, controllers have greater ability to monitor all functions, record and compare each function to manufacturer specifications to determine on a real time basis whether a component is performing as designed or has a fault.
In addition to the various different diagnostic software tools, the Star system has had several hardware iterations too. The hardware is generally known as C3, C4, and C5 and are the multiplexer in the system.
(Unlike a cheaper scanning tool, DAS / Xentry needs the multiplexer, or MUX, to access all of the individual car ECUs and modules). Each iteration of the hardware improved on connectivity with the car and faster data transfer speed between the car and the tool. The complete Star tool consists of two primary components, a multiplexer (muxer) and a computer (laptop, handheld tablet, or such). The muxer connects to the car with an interface cable that connects from the OBDII. (Star kits typically come with several cables as some older cars and other types of vehicles do not have an OBDII connection port, ie the earlier R170s.) The muxer is then connected to a computer (laptop, handheld tablet, or such) by either a serial cable (C3 system), networking cable (C4 or ), or wirelessly (C4 or C5) .
A side note here the C3 systems are generally easier to setup and use as they dont have the extra networking overhead to worry about this may not be an issue for some people, but for others it can be a real stumbling block.
The computer uses proprietary software to access and deliver the data coming through the muxer. HHT, DAS and Xentry are the names of the three generations of the software. Each controller will report all events or faults. The Star system allows for those faults to be investigated to better understand what is occurring. As the investigation goes deeper, Star provides pictures, operating parameters, and specific tests so that it can be determined if a component is within specification or needs to be replaced/repaired, and also links to WIS (Workshop Information System for further detailed instructions relating to the job at hand more on this shortly).
As an example for this write up, a Star DAS diagnostic session was run on a 2006 SLK 350. As mentioned, Star actually has three different diagnostic tools HHT, DAS and Xentry. At the start of a diagnostic session, the software determines based on the car to be tested, which of those three software tools to use. In the stated example, the system ran DAS to query the car and report back any faults. The result of the session shows a stored fault code 9101 Fan N22/7b1 (In-car temperature sensor). When that fault is selected from the fault reporting screen for further investigation, the following screen is shown:
This screen shot has a picture of component N22/7, which is the Convenience Automatic Climate Control (C-AAC) in-dash control unit (pics of front, back, and electrical connections). The fault is listed as the Fan N22/7b1, which is a sub component of N22/7. It is the small fan that circulates interior air over the temp sensor that is located behind the center horizontal slots of the in-dash A/C unit. It is this temp sensor that determines how much heating or cooling is needed in the car.
The left side of the screen shows the necessary steps to determine whether this fan is functioning. As shown, the fan speed is reported at 12rpm while the spec is 500rpm. The next step would be to select F4 No as the measured value of 12rpm does not match the spec of 500rpm. When F4 is selected, the next screen will state that the control unit N22/7 is defective (the small fan and other parts within the control unit are not serviceable) and needs to be replaced since the fan is not pulling air over the temp sensor in the in-dash unit and thus can not tell what the temp is within the interior of the car.
This is a simple example as to the depth the Star system goes to report faults of every kind within the car. In many cases, there will be several tests for a conclusive diagnosis of the fault. Each test clearly lists and values that should be found.
Additionally, integrated within Star are other MB tools. While using Star you can also access WIS (Workshop Information System complete in-depth service and repair manuals) and EPC (Electronic Parts Catalog). One other tool is Star Finder that will provide a photo and location of every component, sensor, switch, and connector (yes, every connector) within the car this is a REALLY hand tool.
As an example, if Star reports a short in connector X23/6 Vario Roof Limit Switch Connector, Star Finder will provide you with this picture of that specific connector as shown here:
Star is also used when components are replaced. Many components like a SAM (Signal Acquisition Module), DCM (Door Control Module), ECU (Engine Control Module), and others, typically need to be coded to the car. This coding links the module to the car and the specific options and features of that car. The Star system is needed to complete this necessary coding so the replacement module will function properly. If the new control module did not know the options, features, and other functions of the car, it would not know how to interact with the other controllers.
Star provides access to many common functions and features that can either be switch on/off or tweaked to the owners needs or local geographic needs for operating the car. Many of these functions and tweaks can be reviewed in this thread: https://www.slkworld.com/das-star-coding/188241-common-easy-do-das-tweaks.html
The Star system is not the only tool that can read fault codes of your SLK or other MB cars. Although, it is the only system that can communicate with every controller and operate through the controller to test and diagnose faults. More generic code readers either read only the faults of a few major controllers or limited to only the engine fault codes. Some scanners can not actually clear codes, but simply report them. None of these other scanners provides diagnostic solutions or can code new controllers to the car.
The Star system is a fully integrated solution to determine faults, troubleshoot, locate components, sensors, and connectors, provide a solution to remove the fault, and assist with the installation of new components through required computer coding of that new component.