PCV System Monitor - Turbocharged Engine With Map Sensor

The fresh air hose connects the Air Induction System (AIS) to the rocker cover to provide fresh, filtered clean air into the crankcase as the crankcase vapors are evacuated. The PCV valve has a spring loaded, tapered pintle and orifice that limits the amount of crankcase vapors that are inducted into the engine. The least amount of flow occurs during idle when manifold vacuum is high. As engine load increases, manifold vacuum decreases which allow more flow. Under boosted conditions, there is no flow through the PCV valve. As crankcase pressure increases, blow by vapors get pushed through the fresh air tube into the Air Induction System (AIS) where they will be inducted into the engine.

Starting in the 2015 MY, Ford will be using a Crankcase Pressure Sensor (CKCP) to detect a disconnection of the fresh air hose. A disconnection of the fresh air hose would allow the discharge of crankcase vapor into the atmosphere while the engine was under boost. The diagram below shows a schematic of the PCV system. The CKCP sensor is installed in the fresh air hose. The fresh air hose has two connection points. The connection at the AIS system is called the "Clean side" connection while the connection at the rocker cover/engine is called the "dirty side" connection.

Courtesy of FORD MOTOR CO.

Courtesy of FORD MOTOR CO.

Multiple tests are used to detect fresh air hose disconnects. Dirty side disconnects are detected during engine cranking by looking for the absence of a crankcase pressure dip or pulsation. Clean side disconnects are detected during normal driving by detecting the absence of a pressure drop at higher airflows.

Courtesy of FORD MOTOR CO.

Clean Side Monitor: 

The crankcase pressure is linearly regressed during normal driving where pressure samples are collected in higher air flow regions. Once a calibratable number of data samples are collected, the slope of the regressed line is then compared to a threshold to determine if the PCV hose is disconnected from the AIS (faulted if slope near zero). A fault will set a P04DB DTC, Crankcase Ventilation System Disconnected The CKCPM Clean Side diagnostic robustness depends on sufficient samples at high Air Mass flows (>12 lbm/min and higher range). This was the design approach chosen to mitigate the noise factors which are negligible at high air masses.

Courtesy of FORD MOTOR CO.

Dirty Side Monitor: 

The CKCP sensor expects to read a vacuum in the crankcase during the crank and run-up period. This vacuum is the result of the PCV valve opening due to the increased intake manifold vacuum during the engine run-up. This vacuum "dip" signal (along with the pressure pulsation signal) indicates that the PCV fresh air hose is connected at the dirty/crankcase side.

Different crank throttle profiles create different crank manifold pressure pull-downs. The revised 2016 MY diagnostic starts and stops looking for dip based on feedback from MAP sensor. With a "sticky at crank" PCV valve, the CKCP sensor sees more pulsation and a slight positive (rather than dip or flat) pressure indicating operating PCV. The 2016 MY diagnostic takes into account both positive and negative pressure pulsations.

During crank and run-up and prior to entering "run" mode (i.e. low manifold vacuum) the following are calculated:

• Dip Metric: the pressure signal is corrected for any senor offset and integrated.
• Pressure Pulse Metric: the pressure pulse signal amplitude is calculated.

The value is then compared to a threshold to determine if the PCV hose is disconnected from the crankcase. A fault will set a P04DB DTC, Crankcase Ventilation System Disconnected.

The CKCP sensor is checked for circuit/electrical faults (P051C/P051D). The CKCP sensor is also checked for inrange faults using an offset check prior to engine cranking and a rationality test after start. If the sensor offset is greater than a calibrated threshold just prior to engine cranking, a P051B DTC is set. The CKCP sensor is also checked for low readings when air flow rate is low. (There shouldn't be a high pressure drop across the air filter at low flows.), and also checked that high readings (There shouldn't be a condition where the pressure across the air filter gets higher than ambient pressure.).