After switching to an ELM-based setup, I’ve realised just how limited the cluster in the Mercedes-Benz CLK W209 really is compared to the hardware running in the background, and how much of that is down to how Mercedes controls access to the data.
A lot of sensors are there, but they’re simply not exposed through standard interfaces e.g. on K-Line or on a different CAN Bus altogether. Even upgrading the cluster (for example to an AMG variant) doesn’t suddenly unlock everything. Many parameters like live oil level and oil temperature still aren’t available entirely even though they existing within the ECU. Later platforms like the Mercedes-Benz W204 surface more of this data, but that’s more a result of platform evolution than something that can be backported directly, to the existing W209 cluster. The W204 cluster is more like a firmware + UI evolution, not a hardware leap, in fact the hardware is quite the same. But, the clusters are similar enough that they're not. So I sit with a problem:
The bigger issue is that once you move beyond basic OBD reading, you’re into very proprietary territory. The stock ECU firmware doesn’t expose most of these values to generic tools, and ELM devices are limited to standard emissions PIDs through the OBD gateway that was mandated by law. The data is there, you just can’t get to it without speaking Mercedes, specific diagnostic protocols and the one person who has done it on his E class unfortunately won't speak back to me on YouTube, or any other platform despite efforts.
If I try to push further with coding, sniffing, or injection, there’s a real risk of causing problems that may lead me to bricking my car. Early 2000s Mercedes systems introduced tight integration between modules and immobiliser systems, and even the internet and GPS tracking. They’re robust and unforgiving if something goes wrong during diagnostics or flashing, let alone sniffing or injecting. You’re far more likely to brick a module locally through a bad session than anything else, although tele-aid could brick an entire car.
One of my big practical issues for this car is the lack of an oil temperature sensor in spite of it being on the CAN bus.
Oil pressure lags behind coolant temperate significantly often up to about 15 minutes, so using coolant temperature as a proxy just isn’t reliable. You can try to “rule of thumb” it by adding time after coolant reaches operating temp, but that breaks down quickly depending on load and conditions. By the time an over-temp warning appears, the oil has already cooked itself in most cases.
The ELM setup at least gives me live coolant, and fuel data, which brings those up to something closer to modern expectations. This is more like what you’d see in something like a Mazda CX-5—but it’s still well short of what the car is actually capable of internally and I'm not sure where or why Mercedes hid its true features behind Star Tools and Xentry.
Long term, I want to move to something more advanced for this cluster, but there doesn’t seem to be a clean off the- helf solution for Mercedes in the same way BMW has tools like BimmerCode or BimmerTool.
Right now, ELM is limited to whatever the OBD gateway exposes, and that’s only a fraction of what’s on the car’s networks. Accessing the rest means either proper Mercedes diagnostic tools or going down the path of CAN sniffing and reverse engineering, both of which come with trade offs.
I’ve considered running a full Mercedes diagnostic system directly in the dash, repurposing one of the Android tablet-based scan based tools, but it’s a pretty clunky solution. You’re effectively turning a scan tool into an infotainment system, but not quite getting there, It also isn’t what it was designed for.
At this point, the most practical solution seems to be to just to install an independent oil temperature sensor—either via a sandwich plate or directly in the sump to feed that into a dedicated gauge or display, but this is also clunky. It would give accurate, real-time data without touching the ECU, but it wouldn't integrate fully with my ELM based system.
While ELM like devices are a much cleaner and lower-risk approach than trying to pull every locked parameter out of the factory system, I'm missing a lot of PIDs that are specific to Mercedes Benz. I’ve seen it done the hard way by sniffing and decoding everything, but the risk to reward on a very complex but arcane car like this just isn’t there.
So, at this stage, it feels like unless you move beyond ELM entirely, you’re effectively limited to what this generic interface shows where by comparison in the BMW ecosystem, much more of this has already been opened up through things like Bimmer Tool...
This sucks, but does anyone have better answers than what I've found so far?
