Mercedes-Benz W204 OM646 does not start when cold
W204 OM646 does not start when cold, what could be the cause?
The cause varies from car to car. Common ones are leaking injectors, a faulty glow plug relay, a coolant temperature sensor giving wrong information and the crankshaft or camshaft position sensor. The fault should be diagnosed with a diagnostic tool before replacing parts.
Why does the W204 OM646 crank but not start when cold even though there are no fault codes?
The glow plug relay can be faulty without any fault message or the glow light coming on. The temperature sensor can also report too high a temperature for a cold engine, so that glowing and fuel delivery go wrong. Check the sensor reading with a diagnostic tool when the engine is cold.
Are the raised revs and rough running of a W204 OM646 normal when cold?
After starting, a cold engine runs at higher revs for a few seconds, a little longer in frost. That is normal when the heater is not in use. If the engine stalls, runs unevenly for a long time or does not start, the fault must be investigated.