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Home >> Isuzu >> 1999 >> Trooper Part Time >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Trouble Code Identification >> DTC P0401: EGR Flow Insufficient >> Diagnostic Aids

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 problem. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

  1. Perform On-Board Diagnostic (OBD) System Check. See BASIC DIAGNOSTIC PROCEDURES article. 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 CLOSED STUCK . If DTC P1404 is not set, go to next step.
  3. Start engine. Using scan tool, monitor MAP signal. Quickly press throttle half way down and release. If scan tool value does not make an immediate large change, replace MAP sensor. If scan tool value made an immediate large change, go to next step.
  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 IGN, go to last step completed in this DTC test. If scan tool does not display DTC P0401 FAILED THIS IGN, repair is complete.
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