P0401

Circuit Description

This diagnostic test checks for an EGR system malfunction. EGR operation will cause variations in Manifold Absolute Pressure (MAP) because when the EGR valve opens, exhaust gas is drawn through it with intake manifold vacuum. When all test enable conditions are met, the test begins with the PCM cycling the EGR from OFF to ON to OFF and recording the change in MAP. The PCM then calculates the MAP error, or the difference between the actual MAP change and the MAP change that the PCM expected to see. The PCM performs this test several times to gain an average. If at least 6 tests have occurred, the PCM compares its current average MAP error to the failure limit. If the current average MAP error is 4 kPa or more, DTC P0401 is set. If the error is below the limit, EGR operation is returned to normal software control.

Conditions for Running the DTC

^ DTCs P0107, P0108, P0117, P0118, P0122, P0123, P0502, P0506, P0507, P1406, P1508 and P1509 not set.
^ Ignition voltage between 11 and 15 volts.
^ ECT between 80°C (176°F) and 110°C (230°F).
^ Vehicle speed between 20 and 70 MPH.
^ Throttle position 1 degree or less.
^ Transaxle gear has not changed in 0.3 seconds.
^ TCC has not cycled in 0.3 seconds.
^ EVAP control solenoid state has not cycled in 0.3 seconds.
^ This test has not been performed in 5 seconds.
^ A/C clutch state has not cycled in 0.3 seconds.
^ Barometric Pressure (BARO) is at least 72 kPa.
^ EGR pintle is within 95% of commanded position.
^ IAC has changed less than 1 count in the last 0. 1 seconds.

The following conditions must be met for 0.5 seconds prior to the test:

^ MAP value must not change more than 1 kPa.
^ MAP must be between 24.7 and 44 kPa.
^ EGR pintle position is 0.0 volts (EGR Off).

Conditions for Setting the DTC

When the Conditions for Running the DTC are true the EGR is turned On and held for 0.6 seconds and then turned OFF. The change in MAP during the test is compared to the expected change in MAP. If the average difference between expected and actual MAP change is greater than 4 kPa DTC P0401 will set.

Action Taken When the DTC Sets

^ The PCM disables the EGR valve.
^ PCM maintains transaxle shift adapts at current levels.
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC

^ The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
^ A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
^ A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.
^ Use a scan tool to clear DTCs.
^ Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

3. This checks for a shifted MAP sensor. An accurate indicator of the expected MAP reading for any elevation can be obtained by multiplying the local barometer reading (from the weather service) by 3.4. This will indicate the approximate MAP reading in kPa with the key ON and the engine OFF.
7. If commanding the EGR ON creates the desired increase in MAP or the vehicle stalls during the time EGR is commanded ON inspect the EGR system for intermittent restrictions, blockages and/or leaks. Also check the intake manifold bolt torque. Very slight intake leaks may cause a MAP shift. If no repair is made then the fault is intermittent and not present during testing.