Hi jimoh,
Start with this.
DTC P0401: EGR FLOW INSUFFICIENT
Circuit Description
PCM tests EGR system during deceleration by momentarily commanding EGR valve to open while monitoring Manifold Absolute Pressure (MAP) sensor signal. When EGR valve is opened, PCM monitors change in MAP sensor input signal. PCM compares MAP change to a RPM vs. BARO table. When PCM interprets change in MAP sensor to be out of limits, PCM will set DTC P0401. Number test samples required to accomplish this may vary according to severity of detected flow error. Normally, PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, PCM allows 12 test samples during first ignition cycle following a scan tool CLEAR INFO or a battery disconnect. Between 9 and 12 samples should be sufficient for PCM to determine adequate EGR flow and to pass EGR test. Conditions for setting DTC:
"Â Following DTCs are not set:
à † Throttle Position (TP) sensor.
à † Vehicle Speed Sensor (VSS).
à † MAP sensor.
à † EGR pintle position sensor.
à † Engine Coolant Temperature (ECT) sensor.
à † Misfire codes.
à † Automatic transmission codes.
" Engine coolant temperature is less than 140 °F (60 °C).
"Â Ignition voltage between 11.5 and 16.0 volts.
"Â Vehicle speed is more than 15 MPH.
"Â A/C clutch status is unchanged.
"Â Torque Converter Clutch (TCC) status is unchanged.
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Using scan tool, monitor ACTUAL EGR POSITION and wiggle harness and connectors. A change in voltage will indicate area of fault. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.
Diagnostic Procedure
1. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1404 is also set, go to DTC P1404: EGR STUCK CLOSED. If DTC P1404 is not set, go to next step.
3. Start engine and allow to idle. Using scan tool, monitor MAP signal. Quickly press throttle half way down and release. If scan tool value made an immediate large change, go to next step. If scan tool value does not make an immediate large change, replace MAP sensor.
4. Inspect exhaust system for modifications or leaks. If a problem is found, repair as necessary and go to step 7. If a problem is not found, go to next step.
5. Remove EGR valve and check pintle, valve and passages and adapter for excessive deposits or restriction. Check EGR valve gasket and pipes for leaks. If a problem is found, repair as necessary and go to step 7. If no problem is found, go to next step.
6. Remove EGR inlet and outlet pipes from exhaust and intake manifolds. Inspect manifold EGR ports and pipes for blockage. If a problem is found, repair as necessary, then go to next step. If no problem is found, check for an intermittent problem. See
DIAGNOSTIC AIDS.
7. Read and record FAIL RECORDS data for DTC P0401. Clear DTCs. Start engine and monitor system information screen while moving connectors and wiring harnesses related to EGR valve. If scan tool displays DTC P0401 FAILED THIS IGNITION, go to last step completed in this DTC test. If scan tool does not display DTC P0401, repair is complete.
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Sunday, August 29th, 2010 AT 3:54 PM
