P0404

DTC P0404

CIRCUIT DESCRIPTION
The exhaust gas recirculation (EGR) valve is vacuum operated. Vacuum for the EGR valve control system is supplied by a belt driven vacuum pump. The EGR valve vacuum control solenoid and the EGR valve vacuum vent solenoid work together to control the position of the EGR valve. The engine control module (ECM) monitors the EGR vacuum sensor signal to determine the amount of vacuum that is applied to the EGR valve. The EGR throttle valve is used to create a restriction in the air intake in order to increase the engine vacuum. When the EGR valve is commanded to open, the EGR valve is commanded open, the EGR throttle valve is commanded to partially close. The increase in engine vacuum aids in the recirculation of the exhaust gases when the EGR valve is open. The ECM uses the mass air flow (MAF) sensor to calculate the amount of exhaust gas that is consumed by the engine. When the EGR valve is opened, the MAF rate will decrease. If the EGR vacuum sensor signal is lower than expected and the MAF rate is higher than expected, it is assumed that the EGR valve is not opening enough due to a vacuum problem and Diagnostic Trouble Code (DTC) P0404 sets.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0405, P0406, P0489, P0490, P0500, P0651, P2142, P2144, and P2145 are not set.
- The EGR valve vacuum control solenoid has been commanded to more than 70 percent.
- 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 ECM detects a lower than expected EGR vacuum sensor signal and a higher than expected MAF rate.
- The above condition is met for more than 8 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.

TEST

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Steps 11-13: