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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 P0420: Low Catalyst Efficiency Bank 1, Or DTC P0430: Low Catalyst Efficiency Bank 2 >> 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. 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. Diagnose any other DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Ensure TWC is an original equipment part. Check TWC for dents or discoloration caused by excessive heat. Ensure rattle caused by internal catalyst damage does not exist. If a problem is found, repair as necessary and go to step  6. If no problems are found, go to next step.
  4. Check exhaust system for leaks, damage, loose or missing hardware. If a problem is found, repair as necessary and go to step  7. If no problems are found, go to next step.
  5. Ensure HO2S No. 3, bank 1 is securely installed and that harness is not damaged or contacting exhaust system. If a problem is found, repair as necessary and go to step  7. If no problems are found, go to next step.
  6. Replace affected TWC. Check for possible engine misfire DTC or engine mechanical problem, and go to next step.
  7. Read and record FAIL RECORDS data for DTC P0420 or DTC P0430. Clear DTCs. Start engine and allow coolant temperature to reach 140°F (60°C). Run engine while monitoring scan tool IAC RPM control function to maintain MAF sensor range at 8-50 grams per second for at least 2 minutes. Go to next step.
  8. Using scan tool, monitor TWC MONITOR TEST COUNTER while operating vehicle within conditions required to set DTC. Read SPECIFIC DTC. If scan tool displays DTC P0420 or DTC P0430 TEST RAN AND PASSED, repair is complete. If scan tool does not display DTC P0420 or DTC P0430 TEST RAN AND PASSED, return to step  2.
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