Symptoms: warning message on CID and KOMBI about low oil pressure:
Related error messages:
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30C4 motor oil pressure control, mechanically
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30C6 motor oil pressure sensor, plausibility
30C7 motor oil pressure system
The oil pressure (according to oil pressure map) for N43/N53 series engines is controlled by oil pressure sensor, which is located after the valve (solenoid). The valve is managed via DME by PWM and defines necessary oil pressure, accordingly to engine temperature, RPM, load.
INPA menu, intended to evaluate the oil pressure:
../F6/F2/F2
PWM, supplied to oil pressure valve, is displayed in INPA menu:
../F6/F2/F3
Note: menus are defined for INPA loader 2.023.
Oil pressure menu:
- sollwert: inquired pressure value
- istwert: measured value (attention: incorrect value. Read description below)
Management menu for oil regulation valve using PWM:
Unfortunately, the inspection of data brings disappointment: inquired value of oil pressure (sollwert) DOES NOT corresponds to measured value of oil pressure (istwert): measured value is lower than inquired value, in the same time oil pressure management PWM value typically fluctuates around 35 .. 45% mark. Oil pressure value, measured in idle, display lower than it should be – in red sector – it doesn’t look OK. Information from manufacturer – absolute zero.
Data look totally unusable – in many internet forums the idea about software mistakes is present. And again – no solution.
After little research we can confirm, that yes, there are mistakes. The mistakes are in data displaying! Measured (istwert) value is displayed with a substantial shift -1000 hPa! The most probable cause of such mistake – incorrect interpreting of relative (against atmospheric pressure) and absolute values.
So, when we are looking on the data, we have to INCREASE measured (istwert) values for 1000 hPa! Taking this in to account, it comes out (test of system and driving sessions confirmed it), that everything is OK with oil pressure stabilization – it works in closed loop mode and really maintains the inquired pressure, changing PWM of the valve!
Still significant inconvenience is present – dynamic view of data is very difficult, additionally: PWM parameter of valve management is displayed in other menu. But, if we “correct” the data displaying mistake, mentioned before, we can see, that MSD manages oil pressure, and data are reliable. Accordingly, if the error messages regarding insufficient oil pressure appear, we can “look” for situations, when the system does not manages with keeping the pressure.
Main symptoms:
-
measured value of oil pressure in some area of RPM/torque starts to “lag behind” for more than 1000 hPa (displayed values, before ‘1000 hPa’ correction);
-
the oil pressure valve is being closed significantly (PWM value drops below 20 .. 25%)
Another useful oil pressure test block can be found here:
../F9/F9
Within the test block MSD automatically checks ability to keep different oil pressures (2000/3500/5000 hPa) in idle, 2000 and 3000 RPM.
Note: once test mentioned above is enabled, just slightly press the accelerator pedal to restart the test again. This option is very useful for oil valve observation (test is proceeding even if exact INPA menu is left).
Also evaluating data of this test, we have to “increase” oil pressure value for 1000 hPa. When performing this test, it is very important to follow (also) the oil pressure valve PWM values – if the valve is being closed significantly, obviously the oil pump is not capable to maintain required pressure and/or flow.
There could be many reasons for that – problems with oil “availability” (clogged oil filter, oil suction pipe, etc.), oil pump run-out, too high oil consumption, also the defect of valve itself.
Typically – clogged filter and problems with oil supply would give higher RPM/load range (the pump will not be able to provide the necessary productivity), in turn oil pump run-out will result in problems in area of very low RPM.
It is understandable, that problems with oil pressure are ones of mechanical area, accordingly – they should be trusted to the mechanic, who can evaluate technical condition of the engine “in life”.
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