Low-pressure
Mercedes-Benz/Renault diesel EGR filter clean
CM reader, Tim Baker, looks at a 2017 Mercedes-Benz C200 with the OM626 (Renault R9M) diesel engine with an illuminating Engine Management Light (EML).
With the Engine Management Light (EML) illuminated, this Mercedes-Benz was checked for error codes. P0401 – Exhaust Gas Recirculation Flow insufficient detected.
The vehicle owner said that the car had been to a Mercedes-Benz dealership some time previously and they “had to work on a sensor”. As luck would have it, the owner had kept the invoice, and the detail recorded the same error code we had – and the report indicated that the EGR filter was replaced.
I wanted to begin by retracing the steps of the dealer repair. The error code was the same, and because the labour amount on the dealer invoice was reasonable, this suggested that the repair must have been completed within an hour – so the filter must be located somewhere accessible. Seemed like a good place to start.
It appears that two EGR circuits are employed on this engine: low-pressure and high-pressure. The high-pressure EGR valve may be found under the air inlet duct adjacent to the engine bay bulkhead on the inlet side of the engine at point ‘D’.
The low-pressure EGR valve is located adjacent to the turbo at position ‘E’.
We began work by removing the inlet air duct ‘A’. The MAF sensor is connected to ‘A’ at the junction with ‘B’. Disconnect the harness connection to the MAF sensor.
Here is a caution for air duct ‘B’. This is a hard plastic duct and has no flexibility. The joint between the MAF sensor and duct ‘B’ has no rubber or flexible section, and you may find that the duct ‘B’ has shrunk with age. With duct ‘B’ being of hard plastic, I found it difficult to initially remove ‘A’ and impossible to reconnect ‘B’ to the MAF sensor when reassembling the air inlet duct. Clever design. As this duct ages, it may shrink sufficiently to cause it to split open at either end.
On duct ‘B’ there is a rubber support mounting midway along the unit adjacent to the bulkhead. When I came to remove this, I found it had already been broken away from ‘B’, with one of the cable clip mounting points for one of the sensors attached to ‘B’.
Before removing ‘B’, loosen the jubilee clip at the connection with the EGR mixer at position ‘F’. Disconnect the crankcase breather hose and all harness connections to the sensors installed in ‘B’.
