Mercedes OBD Codes
decoded & explained
The codes Mercedes owners actually see — misfires, EGR, catalysts and diesel-specific faults — with clear causes and fixes.
Mercedes-Benz check engine light codes
Mercedes-Benz uses standard OBD-II for engine diagnostics, so a generic scanner reads the main engine codes. Deeper diagnosis of the CDI diesel and electronic modules is done with Star/Xentry dealer tools.
Below are the P-codes most often reported on Mercedes-Benz models, including common diesel faults.
OBD-II code decoder
—
—
—
Most common Mercedes-Benz
Common Mercedes faults behind these codes.
| Code | Description |
|---|---|
| P0128 | Coolant Thermostat Below Regulating Temperature |
| P0171 | System Too Lean (Bank 1) |
| P0300 | Random/Multiple Cylinder Misfire |
| P0401 | EGR Flow Insufficient |
| P0420 | Catalyst System Efficiency Below Threshold (Bank 1) |
| P0442 | EVAP System Small Leak Detected |
| P2200 | NOx Sensor Circuit Range/Performance |
| P2463 | Diesel Particulate Filter Soot Accumulation |
Common Mercedes-Benz faults
Common Mercedes faults behind these codes.
EGR flow (P0401) — carbon buildup clogs the EGR valve on petrol and diesel models.
Thermostat stuck (P0128) — engine never reaching temperature, common on M274/M276 engines.
NOx sensor (P2200) — frequent on diesel (Bluetec) models with AdBlue systems.
DPF soot (P2463) — city driving prevents regeneration on diesel models.
Misfires (P0300) — ignition coils, spark plugs, or fuel issues.
Mercedes-Benz FAQ
Why does my Mercedes show P0401?
What is a NOx sensor fault (P2200)?
Why does my Mercedes never warm up?
Can I read Mercedes codes myself?
Is the check engine light serious on a Mercedes?
Codes vary slightly by model, year and engine. Always confirm with a proper diagnosis. Manufacturer-specific codes (P1xxx/P2xxx) may differ from generic descriptions.
Continue reading
Stop Coding Alone: OPC-Skills Gives Your AI Agent Superpowers
OpenClaw: Build Your Personal AI Assistant in Minutes
Top 20 AI Tools Every Developer Should Know in 2026
GibsonAI/memori: Structured Memory Infrastructure for Production AI Agents
Decode your Mercedes-Benz code now
Use the free decoder below, or browse the most common Mercedes-Benz codes.