W204 & W212 OBD Pro

Full description

Read your transmission and engine data straight from its control units.
It supports OM646, OM651, M274, M271 Kompressor, M271 CGI engines,
5G-Tronic, 7G-Tronic, and 7G-Tronic (UDS) transmissions.

W204 CDI connects to your car through an ELM327-compatible Bluetooth OBD adapter and goes beyond standard OBD readouts by querying manufacturer-specific diagnostic blocks. This lets you monitor values on your phone that are normally visible only on professional diagnostic equipment.

WHAT IT SHOWS

Current gear — See which gear you are in on a large, readable display.
Selector lever position — P, R, N and D tracked in real time.
Transmission oil temperature — The single most important indicator of transmission health. Watching where oil temperature goes under heavy load, while towing, or on long climbs is valuable for transmission longevity.
Engine coolant temperature — The actual degree reading, unlike the simplified gauge on your dashboard.
Torque converter lockup — The gear display turns green when lockup engages. Converter slip speed is shown below it, so you can observe when and under which conditions lockup occurs.
Injector correction values — The balancing correction (µs) applied by the engine control unit for each of the four cylinders. The spread between cylinders gives an early indication of injector behaviour.

ALERT SYSTEM

Set your own upper limits for coolant and transmission oil temperature. When a limit is exceeded you get an audible and visual warning. After you acknowledge it the dialog will not reappear; only a periodic audible reminder continues until the value returns to a safe range — designed this way so it never blocks your screen while driving.

You can also define a separate threshold for injector imbalance, or turn that alert off entirely. The alarm sound can be chosen from four options and previewed in settings.

SUPPORTED VEHICLES

Engines: OM646 and OM651 diesel engines
Transmissions: 5G-Tronic and 7G-Tronic automatics

The app was developed for these engine and transmission combinations and verified on an actual vehicle. Some values may not be available on cars with different engine or transmission hardware.

REQUIREMENTS

ELM327-compatible Bluetooth OBD-II adapter
Vehicle OBD-II port (below the steering column)

COMING SOON

DPF (particulate filter) soot load and regeneration status

DIAGNOSTIC LOGGING

A session log is recorded on every connection and can be shared as a file. These logs make it easier to investigate an issue or compare values over time.

IMPORTANT NOTES

This app is a diagnostic and monitoring tool; it is not a substitute for professional fault diagnosis. Values are read from the vehicle's own control units, but some scales and thresholds were determined by observation. Consult a qualified workshop before acting on them.

Do not focus on the screen while driving. The app never writes any data to the vehicle — it only reads.

This is an independent project with no official affiliation with, partnership with, or endorsement by Mercedes-Benz AG. Brand and model names are used solely to indicate compatibility.