P0401
Steps 1 - 5:
Steps 6 - 7:
DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient Detected
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 Tech 2 "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. DTC P0401 is a type A code.
Conditions for Setting the DTC
- No TP sensor, VSS, EVAP Purge, IAC, IAT sensor, MAP sensor, EGR Pintle Position sensor, ECT sensor, misfire DTCs set.
- Barometric pressure is above 72 kPa.
- Engine coolant temperature is greater than 60 °C (140 °F).
- System voltage is between 11.5 and 16 volts.
- Vehicle speed is greater than 23 kph (14 mph).
- IAC position is steady, changing less than 5 counts.
- A/C clutch status is unchanged.
Star Test
- TP angle is less than 0.8%.
- EGR duty cycle is less than 1%.
- MAP is steady, changing less than 1 kPa.
- Engine speed is between 1200 RPM and 2000 RPM.
- Compensated MAP between 10.3 kPa and 49.8 kPa.
Run Test
- Delta MAP is recorded during valve open conditions.
- EGR valve is ramped over a time interval.
Run Test will be aborted if any of the following are true:
- Vehicle speed changes by greater than 16 kph (10 mph). Engine RPM changes by greater than 100 rpm.
- EGR is opened less than 95 % of the commanded amount.
During the Start Test and the Run Test, the EGR is closed then opened. The associated change in MAP is compared with the PCM's expected change value. If the difference between the two values exceeds the PCM's internal limit, a Diagnostic Trouble Code P0401 will set. DTC P0401 is a type A code.
NOTE: Several deceleration cycles will be necessary to run a sufficient number of EGR flow tests to determine a "pass" or "fail" condition.
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate the first time the fault is detected.
- A history Diagnostic Trouble Code is stored.
- A history Diagnostic Trouble Code will clear after 40 consecutive warm up cycles without a fault.
- The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
Conditions for Clearing the DTC
- The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history Diagnostic Trouble Code will clear after 40 consecutive warm up cycles without a fault.
- Diagnostic Trouble Codes can be cleared by using the Tech 2.
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 Tech 2 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.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the Diagnostic Trouble Code 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".