P0404A EGR Position Sensor Rationality Failure

NAME OF CODE
EGR Position Sensor Rationality failure

SET CONDITION
The EGR flow or valve movement is not what is expected.

THEORY OF OPERATION
The EGR solenoid assembly consists of a spring loaded potentiometer that rests on the EGR valve pintle, and an EGR solenoid that when actuated will either open or close the EGR valve, allowing more or less exhaust to be diverted to the intake manifold. As the pintle moves, the EGR position sensor provides approximately a 0.8 - 4.3 volt signal to the PCM. The voltage is directly proportional to the valve opening. For a given set of conditions, the PCM knows the ideal EGR flow for optimum NOx and fuel economy as function of the pintle position. If the PCM determines an EGR flow to be not optimal, the PCM will adjust the duty cycle of the EGR solenoid, either opening or closing the EGR valve.

POSSIBLE CAUSES
- EGR valve actuator failure
- Sticky EGR valve actuator
- Loose EGR valve actuator
- Blocked EGR valve actuator
- EGR position sensor failure