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Home >> Buick >> 2004 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls (DTC P0140 To P0496) >> Engine Controls Diagnosis >> DTC P0401 >> Test Description
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Test Description

The number below refers to the step number on the diagnostic table.

  1. 2:  MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.
DTC P0401

Step Action Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Controls Component Views  or  Powertrain Control Module (PCM) Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? Go to Step 2  Go to Diagnostic System Check - Engine Controls
2  Is DTC P0107 or P0108 also set? Go to Diagnostic Trouble Code (DTC) List Go to Step 3 
3 Inspect the exhaust system for leaks, restrictions, and for modification of original equipment manufacture (OEM) parts.
Did you find and correct the condition?		 Go toStep 7  Go to Step 4 
4 Inspect for a vacuum leak between the EGR valve and the intake manifold.
Did you find and correct the condition?		 Go to Step 7  Go to Step 5 
5
  1. Remove the EGR valve. Refer to Exhaust Gas Recirculation (EGR) Valve Replacement .
  2. Inspect the EGR valve pintle and the EGR valve passages for leaks or for restrictions. Refer to Exhaust Gas Recirculation (EGR) System Cleaning orExhaust Gas Recirculation (EGR) Valve Replacement .
Did you find and correct the condition?		 Go toStep 7  Go toStep 6 
6
  1. Remove the EGR valve inlet pipe from the exhaust manifold. Refer to Exhaust Gas Recirculation (EGR) Pipe Replacement .
  2. Inspect the exhaust manifold EGR port and the EGR valve pipe for a restriction.
Did you find and correct the condition?		 Go toStep 7  Go to Diagnostic Aids
7
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
  5. Observe the EGR Flow Test Count parameter on the scan tool. 9-12 EGR Flow Test Counts may be necessary to pass this DTC after the DTCs have been cleared.
Did the DTC fail this ignition?		 Go toStep 2  Go to Step 8 
8 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 Go to Diagnostic Trouble Code (DTC) List System OK
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