Engine
Mercedes OM651 vs OM654
Mercedes diesel comparison for C-Class, E-Class, and GLC buyers deciding between older proven diesel and newer emissions complexity.
Mercedes-Benz OM651
68
/ 100
Mercedes-Benz OM654
72
/ 100
Best used buy
Mercedes-Benz OM654
OM654 for newer, efficient cars with clean emissions data; OM651 for cheaper cars with exceptional service records and no hidden warnings.
The OM654 is the stronger modern choice when diagnostic data is clean. The OM651 can still be durable, but older examples need careful injector, timing, emissions, and battery-voltage checks.
Key differences
- OM651 has more age-related risk and a wider spread of ownership quality.
- OM654 is newer and efficient but still depends on NOx, AdBlue, DPF, and sensor health.
- OM651 value is strongest when records are unusually complete.
- OM654 purchase risk rises sharply if emissions warnings have been cleared recently.
Buyer advice
- Use Mercedes-capable diagnostics, not only generic OBD.
- Verify no AdBlue countdown, NOx history, or repeated emissions repairs.
- Check battery health before trusting electronic fault patterns.
Red flags
- AdBlue countdown
- NOx faults
- Injector correction issues
- Weak battery
- Incomplete service records