P0401

DTC P0401

CIRCUIT DESCRIPTION
The engine control module (ECM) uses the mass air flow (MAF) sensor signal to calculate the amount of exhaust gas recirculation (EGR) flow. The ECM will control the EGR valve vacuum control solenoid and the EGR vacuum vent solenoid to allow vacuum to operate the EGR valve. The EGR control system uses vacuum from a belt driven mechanical pump called a vacuum pump. Diesel engines do not create enough engine vacuum on their own to allow the EGR gases into the combustion process. When the ECM commands the EGR valve to open, the EGR throttle valve will be commanded closed. The EGR throttle valve creates a restriction of incoming fresh air to the engine in order to create engine vacuum. If the ECM detects a calibrated difference between the desired MAF rate and the actual MAF rate during EGR system operation, DTC P0401 sets.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0405, P0406, P0489, P0490, P0500, P0651, P2142, P2144, and P2145 are not set.
- The PCM is not in the Reduced Engine Power mode.
- The Engine Run Time parameter is more than 5 seconds.
- The BARO parameter is more than 72 kPa.
- The Engine Speed parameter is between 610-820 RPM and is steady within 50 RPM for more than 3 seconds.
- The ECT Sensor parameter is between 60-100°C (140-212°F).
- The Calculated Fuel Rate parameter is between 3-20 mm(3).
- The power take off (PTO) is disabled, if equipped.
- The IAT Sensor parameter is more than 0°C (32°F).
- The APP Indicated Angle parameter is less than 1 percent.
- The Ignition 1 Signal parameter is between 11-18 volts.
- The Vehicle Speed Sensor parameter is less than 0.40 km/h (0.25 mph).
- All of the above conditions are met for more than 3 seconds.

CONDITIONS FOR SETTING THE DTC
- The PCM detects a calibrated difference between the expected MAF rate and the actual MAF rate during EGR system operation.
- The PCM detects no difference between the expected EGR vacuum sensor signal and the actual EGR vacuum sensor signal.
- The above conditions are met for more than 4 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
Inspect the MAF sensor for proper operation. An inaccurate MAF sensor signal may cause this DTC to set. Refer to Scan Tool Data List. Scan Tool Data, Normal Values and Definitions

If the condition is determined to be intermittent, refer to Intermittent Conditions. Diagnostic Strategies

TEST

Steps 1-4:

Steps 5-8:

Steps 9-11: