Ford Escape: Engine Emission Control / Description and Operation - Engine Emission Control - System Operation and Component Description

System Operation

Exhaust Gas Recirculation (EGR) Systems

The EGR system controls the NOX emissions. Small amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air to fuel charge. The combustion chamber temperature is reduced, lowering NOX emissions

Exhaust Gas Recirculation (EGR) System — Differential Pressure Feedback

The EGR system consists of an electric motor EGR valve integrated assembly, a MAP sensor, differential pressure feedback EGR sensor, PCM , EGR cooler, exhaust pressure (EP) sensor, and exhaust gas recirculation temperature bank 1, sensor 2 (EGRT12). Operation of the system is as follows:

• The EGR system receives signals from the engine ECT or CHT sensor, TP sensor, CKP sensor, and the MAP sensor to provide information on engine operating conditions to the PCM . The engine must be warm, stable, and running at a moderate load and RPM before the EGR system is activated. The PCM deactivates the EGR during idle, extended wide open throttle (WOT), or whenever a concern is detected in an EGR component or EGR required input. The PCM calculates the desired amount of EGR for a given set of engine operating conditions.

• The EP sensor measures the exhaust pressure by comparing the EP sensor calibrated value to the actual EP sensor value. The EP sensor is used primarily to determine EGR cooler effectiveness and is also used for converting EGR flow to EGR valve position.

• The EGRT12 sensor measures the exhaust gas temperature downstream of the EGR cooler and is monitored by comparing the EGRT sensor calibrated value to the actual EGRT sensor value. The EGRT12 sensor is primarily used for EGR flow caluculation and is also used for EGR cooler diagnostics.

• The monitor checks the electric EGR valve circuits for opens and shorts. The monitor compares the differential pressure feedback EGR sensor to a calibrated value and the electric EGR valve commanded position to determine if EGR flow is present.

• The monitor checks for the differential pressure feedback EGR sensor for opens and shorts. The differential pressure feedback EGR sensor hoses are tested for connection and restriction at idle. The PCM commands the EGR valve closed and the monitor tests for the differential pressure feedback EGR sensor to indicate no flow is present. The PCM commands the EGR valve open and the monitor tests the differential pressure feedback EGR sensor voltage to indicate flow is present. The stop start option on some vehicles requires the hose tests to run during off idle conditions.

• The intake manifold pressure is higher when the EGR is flowing than when it is not flowing. When the exhaust gas is delivered into the intake manifold, the MAP sensor reading increases.

• The exhaust manifold provides a source of exhaust gas to the EGR cooler, EGR orifice tube and EGR valve.

• The EGR cooler is monitored by comparing the EGRT12 and EP sensors calibrated value to the actual EGRT12 and EP sensor values. Under cooling and over cooling conditions are monitored.

Positive Crankcase Ventilation (PCV) System

The PCV system circulates crankcase gases through the intake air system into the engine where they are burned. The PCV system regulates the amount of ventilated air and blowby gases to the intake manifold.

The PCV system equipped with a removable PCV valve, a PCV valve integral to the valve cover, or a crankcase ventilation oil separator, as part of the PCV system. The PCV system on some vehicles will include a crankcase pressure sensor to detect a disconnection of the fresh air hose.

The PCV systems comply with OBD PCV monitoring requirements to prevent accidental disconnection from the valve cover. For more information about the PCV monitor and crankcase pressure sensor, refer to PCV System Monitor in this section.

Positive Crankcase Ventilation (PCV) System Monitor

The PCV system monitor consists of a modified PCV system design. The PCV system is designed to prevent accidental disconnection. High retention force molded plastic lines are used from the valve cover to the intake manifold. The diameter of the lines and the intake manifold entry fitting are increased so that disconnection of the lines may cause an engine to stall. In the event the vehicle does not stall if the line between the intake manifold and PCV system is disconnected, the vehicle has a large vacuum leak that causes the vehicle to run lean at idle. The lean condition illuminates the MIL and stores a lean bank 1 or bank 2 DTC .

The PCV monitor sets a DTC if the PCV vacuum hose is disconnected, or if a large air leak between the throttle body (TB) and intake valves is present. An idle speed symptom may be present when the DTC is set.

The PCV system on some vehicles will include a crankcase pressure sensor 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 fresh air hose connects the intake air system to the valve cover, with the crankcase pressure sensor mounted in the fresh air hose. The PCV monitor will detect a fresh air hose disconnection at the intake air system or the valve cover, by monitoring crankcase pressure sensor changes during engine cranking, and driving with higher intake airflow.

For additional PCV information, refer to Positive Crankcase Ventilation (PCV) System in this section

Exhaust Gas Recirculation (EGR) System Monitor

The EGR system monitor is an on board strategy designed to test the integrity and flow characteristics of the EGR system. The EGR system monitor consists of an electrical and functional test that checks the electric EGR valve and the EGR system components for correct operation.

After the vehicle has warmed up and normal EGR rates are being commanded by the PCM , the low flow check and the high flow check is carried out. The EGR flow diagnostics execute once per driving cycle and are designed to set a DTC when the total mass flow error results in an emissions increase above a calibrated level.

• The EGR system uses inputs from the ECT sensor or CHT sensor, the IAT sensor, the CKP sensor, the MAP sensor, EGRT bank 1, sensor 2 (EGRT12), exhaust pressure (EP) sensor, differential pressure feedback EGR sensor and vehicle speed to provide information about engine operating conditions to the PCM .

• The PCM uses the sensor inputs to determine the desired amount of EGR gas flow and controls the EGR valve to achieve the desired EGR flow rate.

• The EP sensor measures the exhaust pressure by comparing the EP sensor calibrated value to the actual EP sensor value. The EP sensor is used primarily to determine EGR cooler effectiveness and is also used for converting EGR flow to EGR valve position.

• The EGRT12 sensor measures the exhaust gas temperature downstream of the EGR cooler and is monitored by comparing the EGRT12 sensor calibrated value to the actual EGRT12 sensor value. The EGRT12 sensor is primarily used for EGR flow caluculation and is also used for EGR cooler diagnostics.

• The monitor checks the electric EGR valve circuits for opens and shorts. The monitor compares the differential pressure feedback EGR sensor to a calibrated value and the electric EGR valve commanded position to determine if EGR flow is present.

• The monitor checks for the differential pressure feedback EGR sensor for opens and shorts. The differential pressure feedback EGR sensor hoses are tested for connection and restriction at idle. The PCM commands the EGR valve closed and the monitor tests for the differential pressure feedback EGR sensor to indicate no flow is present. The PCM commands the EGR valve open and the monitor tests the differential pressure feedback EGR sensor voltage to indicate flow is present. The stop start option on some vehicles requires these hose tests to run during off idle conditions.

• The intake manifold pressure is higher when the EGR is flowing than when it is not flowing. When the exhaust gas is delivered into the intake manifold, the MAP sensor reading increases.

• The exhaust manifold provides a source of exhaust gas to the EGR cooler, EGR orifice tube and EGR valve.

• The EGR cooler is monitored by comparing the EGRT12 and EP sensors calibrated value to the actual EGRT12 and EP sensor values. Under cooling and over cooling conditions are monitored.

Component Description

Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor

The differential pressure feedback EGR sensor is a piezo resistive type pressure transducer that monitors the differential pressure across a metering orifice located in the orifice tube assembly. The differential pressure feedback EGR sensor receives this signal through 2 hoses referred to as the downstream pressure hose (REF signal) and upstream pressure hose (HI signal). The HI and REF hose connections are marked on the differential pressure feedback EGR sensor housing for identification (note the HI signal uses a larger diameter hose). The differential pressure feedback EGR sensor outputs a voltage proportional to the pressure drop across the metering orifice and supplies it to the PCM as EGR flow rate feedback.

Electric Exhaust Gas Recirculation (EGR) Valve

The electric EGR valve is either a water cooled or an air cooled motor and valve assembly. The motor is commanded to move in 52 discrete steps as it acts directly on the EGR valve. The position of the valve determines the rate of EGR flow. The spring works to close the valve against the motor opening force.

Exhaust Gas Recirculation (EGR) Cooler

The exhaust gases are directed through the EGR cooler to lower the exhaust gas temperature before entering the intake manifold. The EGR cooler uses engine coolant to reduce the exhaust gas temperature.

Exhaust Gas Recirculation (EGR) Orifice Tube Assembly

The EGR orifice tube assembly is a section of tubing between the exhaust manifold and the EGR valve. The assembly provides the flow path for the EGR to the intake manifold and also contains the metering orifice and 2 pressure pick up tubes. The internal metering orifice creates a measurable pressure drop as the EGR valve opens and closes. This pressure differential across the orifice is picked up by the differential pressure feedback EGR sensor which provides feedback to the PCM .

Exhaust Gas Recirculation Temperature (EGRT) Sensor

The EGRT bank 1, sensor 2 (EGRT12) is a thermistor device in which resistance changes with temperature. The EGRT 12 sensor is an input to the PCM . The electrical resistance of the sensor increases as the temperature decreases, and the resistance decreases as the temperature increases. The varying resistance changes the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

The EGRT12 sensor is primarily used for EGR flow caluculation and is also used for EGR cooler diagnostics. The EGRT12 sensor monitors the exhaust gas temperature downstream of the EGR cooler. The EGRT12 sensor is located between the EGR cooler and the EGR valve on the EGR orifice tube assembly.

Exhaust Pressure (EP) Sensor

The EP sensor measures the exhaust pressure downstream of the EGR cooler. The EP sensor signal is used primarily for EGR cooler effectiveness. The EP sensor is located between the EGR cooler and the EGR valve on the EGR orifice tube assembly.