Change Car Glow Plugs Mercedes-Benz 200 - 500

Glow plugs are used in diesel engines to preheat the combustion chamber before starting, particularly in cold weather. Unlike petrol engines that use spark plugs to ignite the fuel, diesel engines rely on compression ignition. Modern glow plugs also remain active after starting to reduce emissions and noise during the warm-up phase.

Generally, glow plugs last between 80,000 and 160,000 km. Symptoms of failing glow plugs include: difficulty starting in cold weather, white or grey exhaust smoke on start-up, rough idle during warm-up, the glow plug warning light remaining illuminated, and increased fuel consumption.

Via the EOBD diagnostic system, faulty glow plugs will trigger fault codes (typically P0380–P0384 for glow plug circuit faults). Individual glow plug resistance can be measured with a multimeter (typically 0.5–2 ohms for a good plug).

Difficulty level 3/5: intermediate. Glow plugs can seize in the cylinder head over time due to heat and corrosion, making removal difficult and risking breakage. Key steps: warm the engine first, apply penetrating oil, use the correct glow plug socket, unscrew carefully (do not force — a broken glow plug requires specialist extraction).