SW1 L4-1.9L SOHC VIN 8 (1996)
The linear EGR system consists of a linear EGR valve, the PCM and its associated wiring. The PCM directly controls the ground for the EGR valve
when certain conditions have been met. Voltage is supplied by the UHJB to the EGR valve when the ignition is turned On. When the PCM grounds the
valve, a diagnostic feedback signal can determine if the valve had actually moved. Since the correct feedback voltage is possible, but the passage has
restricted flow, P0401 was implemented.
DTC PARAMETERS
EGR flow restrictions are diagnosed during a deceleration. The EGR valve is commanded closed during a normal deceleration. To run the P0401 test the
valve is opened during deceleration and a change in MAP is expected. If the change in MAP is below a threshold it indicates flow is restricted.
DTC P0401 will set if a calculated value compared to an engine speed vs barometric pressure determines there is a restriction in EGR flow when:
