Description & Operation
The exhaust gas recirculation (EGR) system is used to lower the emission levels of oxides of nitrogen (NOx) that form during the combustion process. NOx levels are based on the amount of oxygen in the combustion chamber, and the length of time that combustion temperatures exceed 816C (1,500F). The EGR system lowers the combustion temperatures, thus lowering the level of NOx.
The EGR valve is designed to supply EGR to the engine. The EGR valve consists of a sealed bobbin and coil assembly, or solenoid. Inside the solenoid is a sleeve-armature assembly that contains a pintle and valve, two seals, retaining washers, a seal spring, and armature spring, and a bearing. The bearing seals the pintle valve shaft from the exhaust chamber. Also, a shield, held in place by a compression spring, deflects exhaust gas from the shaft and armature.
The powertrain control module (PCM) uses the pintle valve to control the EGR flow into the engine. Exhaust gas is routed from the intermediate exhaust pipe to the valve through a feed pipe. When the PCM commands the EGR valve open, the exhaust flows through the EGR valve, past the pintle and into the engine via the crossover water pump housing. When the throttle valve opens, the exhaust gas mixes with the incoming air. When the combination of air/fuel/exhaust gas is burned in the chamber, a portion of the heat energy is absorbed by the exhaust gas. This helps to lower the level of NOx emissions.
The PCM monitors the pintle position using the signal from the EGR pintle position sensor. The sensor is an integral part of the EGR valve. The PCM supplies the pintle position sensor with a 5-volt reference and a ground. The pintle position sensor provides a signal voltage to the PCM. By monitoring the voltage on the signal line, the PCM is able to determine if the EGR valve responds properly to commands from the PCM. As the EGR valve position changes, the pintle position signal voltage will change. With the EGR valve closed, the signal voltage is near 0 volts. However, the pintle position signal voltage increases as the EGR valve opens.
Too much EGR flow tends to weaken combustion, causing the engine to run rough and/or stall. With too much EGR flow at idle, cruise, or cold operation, any of the following conditions may occur:
DTC P0300 Misfire Detected
If the EGR valve is stuck open, the engine may not run. Too little or no EGR flow allows combustion temperatures to get too high during acceleration and load conditions. This could cause:
Poor fuel economy. EGR flow diagnosis is included in the DTC P0401 diagnostic table. Pintle position error and control circuit diagnosis is covered in DTCs P0403, P0404, P0405, and P1404. If EGR DTCs are encountered, refer Diagnostic Trouble Code (DTC) List in the appropriate section.