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DTC P0401 - INSUFFICIENT EXHAUST GAS RECIRCULATION (EGR) FLOW DETECTED
CAUTION:If ECM replacement is instructed in following testing, always ensure ECM connectors and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction.
The EGR system recirculates exhaust gas through intake system to reduce combustion temperature and NOx emissions. The amount of EGR valve opening is regulated by the EGR vacuum modulator according to engine load. Vacuum source to valve is controlled by the Vacuum Switching Valve (VSV), which is controlled by ECM.
The EGR valve is closed (VSV on) under the following conditions:
Engine is not warmed up.
Vehicle under deceleration.
Light engine load.
DTC is set when EGR temperature sensor value does not exceed ambient air temperature by more than 104 F (40 C) after vehicle is operated for 3 to 5 minutes (50 MPH or more). Possible causes are:
EGR valve stuck closed.
VSV short circuit.
EGR temperature sensor open circuit.
EGR vacuum hose disconnected.
Friday, February 27th, 2009 AT 5:17 PM