What does it mean?
OBD II fault code P06DD is a generic trouble code that is defined as, “Engine Oil Pressure Control – Circuit Performance Problem”, or sometimes as “Engine Oil Pressure Control Circuit Performance/Stuck Off”, and is set when the PCM (Powertrain Control Module) detects that the engine oil pressure is above or below predefined allowable thresholds, given current operating conditions.
Note that allowable pressure thresholds are different for different engines, as is the time required for the code to set while the actual oil pressure deviates from the desired when the oil pressure control solenoid is in the “ON” position.
NOTE: Note that this code only applies to vehicles with variable geometry oil pumps that can be adjusted to increase or decrease the oil pressure under different operating conditions both to satisfy changing lubrication requirements and to reduce parasitic power losses. Although internal combustion engines have reached a very high level of technical sophistication, even the most advanced engines are only about 30 percent efficient*, with the other 70 percent going to waste in the form of heat.
Most of this heat is caused by internal friction and pumping losses, and although engineers have devised several highly sophisticated combustion processes to extract more energy from liquid fuels, the problem remains that friction, pumping losses, and parasitic power losses caused by ancillary equipment, and even by critical engine components, still make modern engines about 70 percent inefficient. * This figure is about 40 percent for diesel engines since diesel fuel contains more energy per unit of volume than gasoline does.
As a practical matter, modern internal combustion engines of all types and designs have reached a point where they can for all practical purposes, not be developed any further without essentially, rethinking the concept of liquid fuel combustion.
However, with the rapid pace of developments in electric vehicle technology, no car manufacturer is going to invest hundreds of billions of dollars into developing entirely new liquid fuel combustion technologies, and the engines to go with those technologies. In fact, most major car manufacturers have ceased any further development of combustion technology in favor of developing electric cars and their related technologies.
In the real world though, large-scale adoption of electric vehicles is still a decade or two away, and in the meantime, car manufacturers still have to contend with exhaust emissions regulations that become stricter every year.
So, from design, engineering, and cost perspectives, the only aspect of internal combustion engines that can still be somewhat developed is methods and ways to decrease, if not eliminate parasitic power losses caused by things like oil pumps, water pumps, radiator fans, and alternators whose output cannot be adjusted, regulated, or even turned off completely for short periods. Thus, as far as oil pumps are concerned, the problem is that their output is fixed, and tied to engine speed.
Put differently, this means that an oil pump delivers a fixed volume of oil per engine revolution, and as the engine speed increases, the pump delivers more “fixed volumes” of oil per unit of time, which increases the total volume of oil the pump delivers. However, since the oil pump has a fixed geometry, and, therefore, a fixed output per engine revolution, the oil pressure remains constant on many engines.
Again, put differently, this means that increasing the engine speed on many engines increases only the volume of oil the pump displaces, while the overall pressure remains constant, or varies very little. As a result of the above, the high amount of torque required to drive the oil pump at low engine speeds robs especially small-displacement engines of significant amounts of power.
More to the point though, the effort required to drive the oil pump also requires more fuel than is strictly necessary, which has the corollary that inc