Vehicles using OM660.940 engine list:

Engine OM660.940

Symptoms:
- Rough idling and loss of power
- Difficulty starting, especially in cold conditions
- Excessive smoke from the exhaust
- Engine warning light illumination
- Unusual noises such as knocking or ticking

Diagnosis:
- Check for clogged fuel injectors or fuel filter issues causing poor fuel delivery
- Inspect glow plugs for proper operation, as failure affects cold starts
- Examine the EGR valve for carbon buildup leading to rough running
- Test the turbocharger for wear or boost leaks impacting engine performance
- Scan the engine control unit (ECU) for fault codes related to sensors or emissions

Fixes:
- Clean or replace fuel injectors and fuel filter to restore proper fuel flow
- Replace faulty glow plugs to improve cold start reliability
- Clean or replace the EGR valve to prevent rough idling and emissions problems
- Repair or replace the turbocharger if boost pressure is insufficient or if mechanical damage is found
- Address any sensor faults by replacing defective components and clearing ECU codes

Prevention:
- Use high-quality diesel fuel and replace fuel filters regularly to avoid injector clogging
- Perform routine maintenance on the glow plug system before cold seasons
- Regularly clean the EGR valve and intake system to prevent carbon buildup
- Monitor turbocharger health during service intervals and avoid prolonged high engine loads without proper warm-up and cool-down
- Keep the engine management system updated and promptly address warning lights to prevent further damage

By adhering to these diagnostic steps, fixes, and preventive measures, owners of Smart city-coupé and fortwo CDI models with the OM660.940 engine can maintain reliable performance and extend engine life.