Tuesday, 17 May 2016

Engine malfunctioning without recording of fault codes

On this occasion, we are going to repair a fault that affects the BMW 3 series with M57 and M57N diesel engine.


The engine malfunctions during different operating phases, for example, while accelerating, on starting the engine from cold and/or when travelling at a constant speed at low rpm.

After carrying out a diagnostic reading, no fault code can be seen recorded relating to the engine problems.

One of the causes of this anomaly is that there is a deterioration in the fuel rail sensor connector or in the sensor wiring.


To carry out a repair, check to see if a fault code has been recorded with a diagnostic tool. Then carry out an injector correction reading to verify that one of the injectors has an incorrect value and rule out possible problems. At this point, check that on moving the pressure sensor connector by hand, the engine provides an easily perceptible positive response.

After the above results, the connection problem is shown to be in the fuel rail pressure sensor. To resolve this incident, the fuel rail pressure sensor wiring should be removed and replaced with a specific kit from the manufacturer.

The kit contains a new connector that must be connected to the sensor and the wires should be directly connected to the engine control unit (ECU), after removing the wires from terminals 20, 33 and 35.

After their removal, the brown/green wire from the sensor connector should be connected into terminal 20 of the control unit, then the blue/black wire into terminal 33 and lastly the white and yellow wire into terminal 35.

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