P0401

DTC P0401 EGR Flow Insufficient




Circuit Description
The powertrain control module (PCM) tests the exhaust gas recirculation (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 monitors the change in MAP input signal. The PCM compares the MAP change to a RPM vs. BARO table. When the PCM interprets the change in MAP to be out of limits, the PCM will set DTC P0401. The number of test samples required to accomplish this may vary according to the severity of the 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
- No TP sensor, vehicle speed sensor (VSS), misfire, IAC, IAT sensor, MAP sensor, EGR Pintle Position sensor, ECT sensor, misfire, or automatic transmission DTCs set.
- Barometric pressure is above 75 kPa.
- Engine coolant temperature is greater than 60 °C (140 °F).
- Ignition voltage between 11.5 and 16 volts.
- Vehicle speed is greater than 24 kph (15 mph).
- IAC position is steady, changing less than 10 counts.
- A/C clutch status is unchanged.
- TCC status is unchanged.

Start Test
- TP angle is less than 1%.
- EGR duty cycle is less than 1%.
- MAP is steady, changing less than 2 kPa.
- Engine speed is between 1100 RPM and 2000 RPM.
- MAP between 10 kPa and 40 kPa.
- The test will be aborted if the vehicle speed changes by more than 16kph (10 mph), engine speed changes by more than 100 RPM or the EGR is opened less than 95% of commanded position.
- The PCM will only run the EGR test during a closed throttle condition.
- The PCM will only run the EGR test at vehicle speeds above 24 kph (15 mph).
- Several deceleration cycles will be necessary to run a sufficient number of EGR flow tests.

Diagnostic Aids
Check for the following conditions:
- Poor connection or damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the Actual EGR Position display on the scan tool while moving connectors and wiring harnesses related to the EGR valve. A change in the display will indicate the location of the fault.
- Ensure EGR valve is correctly mounted. See On-Vehicle Service.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

NOTE: If the EGR valve shows signs of excessive heat, check the exhaust system for blockage (possibly a plugged catalytic converter) using the Restricted Exhaust System Check.

Steps 1 - 4:

Steps 5 - 8:

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart
3. A malfunctioning MAP sensor can set an EGR DTC. The MAP sensor could send a constant signal which is not low enough to set a low MAP DTC. The constant signal from the MAP sensor also may not be high enough to set a high MAP DTC. This step verifies that the MAP sensor is responding.