P0401

DTC P0401

CIRCUIT DESCRIPTION
The engine control module (ECM) controls the EGR valve opening based on the atmospheric pressure, engine speed, engine coolant temperature, intake air temperature and fuel injection quantity. The ECM controls the EGR valve by controlling the EGR DC motor. The EGR valve position is detected by the EGR position sensor, and relayed to ECM. When the proper enabling conditions are met, the ECM will open the EGR valve while monitoring the mass air flow (MAF) signal. An expected MAF difference should be detected between the closed and open positions. If the ECM detects the MAF difference less than expected, this DTC will set.

This DTC will only run once per ignition cycle within the enabling conditions.

Condition for Running the DTC
- DTCs P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0201, P0202, P0203, P0204, P0261, P0264, P0267, P0270, P0300, P0301, P0302, P0303, P0304, P0335, P0336, P0403, P0405, P0406, P0478, P0500, P0506, P0507, P0602, P0642, P0643, P1125 P1293, P2146, P2147, P2148, P2149, P2150, P2151, P2227, P2228 and P2229 are not set.
- The battery voltage is between 10-16 volts.
- The ignition switch is ON.
- The engine speed is between 700 - 800 RPM.
- The fuel injection quantity is between 5 - 40 cu.mm.
- The engine coolant temperature (ECT) is between 149-178 °F (65-92 °C).
- The intake air temperature (IAT) is between 19 -246 °F (-7-119 °C)
- The barometric pressure (BARO) is more than 10.9psi (75kPa).
- The accelerator pedal is not pressed.
- The vehicle is stationary.

Condition for Setting the DTC
- The ECM detects that the MAF amount is not within the calculated range for longer than 9 seconds during the EGR flow test. This indicates insufficient amount of EGR flow.

Action Taken When the DTC Sets
- The ECM illuminates the malfunction indicator lamp (MIL) on the second consecutive driving cycle when the diagnostic runs and fails.
- The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Freeze Frame/Failure Records on the second consecutive driving cycle when the diagnostic runs and fails.

Condition for Clearing the MIL/DTC
- The ECM turns OFF the MIL after 3 consecutive driving cycles when the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes after the key is cycled.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic after the ECM turns OFF the MIL.
- Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
- A sticking or intermittently sticking the EGR valve may set this DTC.
- A restricted EGR passage between the exhaust manifold and the EGR valve may set this DTC.

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