Exhaust Gas Recirculation (EGR) Control

Exhaust Gas Recirculation (EGR) Control:

The Exhaust Gas Recirculation (EGR) System removes exhaust gas from the exhaust manifold and pipes it back to the combustion chambers, where it can be burned again. This helps to reduce Oxides Of Nitrogen (NOx) emissions, by reducing combustion temperatures. The EGR valve meters the amount of exhaust gas that is allowed to return to the combustion chambers. The PCM controls the EGR valve, dictating when operation begins and ends, along with determining the amount of exhaust gas that can be efficiently recycled. The EGR valve consists of a solenoid, a pintle, and a pintle position sensor. By energizing the solenoid, the PCM causes the pintle to open and allows exhaust gas to pass through the valve. The solenoid is connected to ignition voltage. The PCM controls the solenoid by grounding the control circuit. By switching the ground on and off, the PCM creates a variable Pulse Width Modulated (PWM) signal that opens the pintle at different rates and to different positions.

The pintle position sensor allows the PCM to monitor the actual position of the pintle, thus enabling it to correct pintle position errors. The sensor is a type of potentiometer, or variable resistor, which provides feedback voltage that is proportional to pintle position. The PCM provides the sensor with 5 volts and a ground. The signal circuit provides the feedback to the PCM. Pintle position is measured in counts, from 0 to 255, with 0 being full closed and 255 full open. However, in practice these limits will not be reached. To compensate for this, the PCM computes a normalized pintle position.