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Message: <blockquote data-quote="CC&#039;S95GT" data-source="post: 1075495" data-attributes="member: 10547">PO401Circuit Description The PCM tests the EGR system during deceleration by momentarily commanding the EGR valve to open while monitoring the Manifold Absolute Pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set DTC P0401.The number of test samples required to accomplish this may vary according to the amount of detected flow error.Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows twelve test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.Conditions for Setting the DTC <ul> <li data-xf-list-type="ul">No TP sensor, Vehicle Speed Sensor, injector circuit, Misfire, IAT sensor, MAP sensor, Idle speed, EGR Pintle Position sensor, ECT sensor, CKP sensor, or MAF sensor DTCs set.</li> <li data-xf-list-type="ul">The AC status does not change.</li> <li data-xf-list-type="ul">The transaxle range does not change.</li> <li data-xf-list-type="ul">TP angle is less than 1% (deceleration).</li> <li data-xf-list-type="ul">Engine coolant temperature is greater than 75Â°C (167Â°F).</li> <li data-xf-list-type="ul">Engine speed is between 1000 RPM and 1250 RPM.</li> <li data-xf-list-type="ul">IAC position is steady.</li> <li data-xf-list-type="ul">MAP steady between 15 and 70 kPa.</li> <li data-xf-list-type="ul">Vehicle speed is greater than 25 mph during deceleration.</li> <li data-xf-list-type="ul">BARO sensor greater than 70 kPa.</li> <li data-xf-list-type="ul">MAP changes monitored during EGR flow test indicate insufficient EGR flow.</li> <li data-xf-list-type="ul">The vehicle will need to be driven above 50 mph, and then allowed to decelerate. When the vehicle is decelerating while meeting all of the criteria listed above, the PCM will enable the test to run. When the test runs, you will see the Desired EGR parameter and the Actual EGR position on the scan tool change from 0 to a calibrated value above 0.</li> </ul>Action Taken When the DTC Sets <ul> <li data-xf-list-type="ul">The PCM will illuminate the MIL during the first trip in which the diagnostic test has been run and failed.</li> <li data-xf-list-type="ul">The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.</li> </ul>Conditions for Clearing the MIL/DTC <ul> <li data-xf-list-type="ul">The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.</li> <li data-xf-list-type="ul">The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.</li> <li data-xf-list-type="ul">The DTC can be cleared by using a scan tool.</li> </ul></blockquote>