Mercedes B‑Class (W246/W247)
Common issues, typical fault codes, and how this platform behaves when things go wrong.
At a Glance
- Use live data and freeze‑frame to prioritise tests (not parts).
- Diesel variants: DPF/EGR behaviour depends heavily on driving profile.
- Petrol variants: misfires and fuel-trim drift often point to air/boost leaks or ignition.
- Best results come from a capable scan tool plus a simple step-by-step plan.
Common Issues on This Platform
- Cooling system faults (thermostat, leaks) causing temperature-related drivability issues on some engines.
- Misfires under load (often plugs/coils first; then air leaks/boost control).
- Air metering or boost leaks leading to lean running and underboost codes.
- Diesel after-treatment issues (EGR/DPF) on short-trip usage profiles.
- Battery/voltage issues can cause wide-ranging symptoms—check basics early.
Typical OBD2 Codes
These codes are common starting points. Always scan the full car and review freeze‑frame and live data before guessing parts.
- P0300 – Random/Multiple Cylinder Misfire
- P0171 – System Too Lean (Bank 1)
- P0299 – Turbo/Supercharger Underboost
- P0016 – Crankshaft/Camshaft Position Correlation
- P0420 – Catalyst Efficiency Below Threshold
- P2002 – DPF Efficiency Below Threshold
- P2463 – DPF Soot Accumulation
- P0401 – EGR Flow Insufficient
How to Approach Diagnostics
- Scan the car and record all engine-related codes, pending codes, and freeze‑frame data.
- Check battery voltage and charging health, especially if multiple unrelated codes are present.
- Confirm basic maintenance: correct plugs, correct oil, clean air filter, no obvious intake leaks.
- Use live data to monitor fuel trims, boost requested vs actual, and misfire counters while reproducing the fault.
- For diesel variants, check DPF soot load and regeneration history before condemning parts.