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Home >> Isuzu >> 1998 >> Trooper S, Standard >> Repair and Diagnosis (Single Page) >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Tests W/Codes - 3.2L & 3.5L >> Self-Diagnostic Tests >> DTC P0446: EVAP Canister Vent Blocked (3.2L) >> Diagnostic Aids

Diagnostic Aids

An intermittent may be caused by a damaged, restricted or disconnected vacuum, vent or purge line. Check for 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. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If DTC P1675 is also set, diagnose DTC P1675 before proceeding. If DTC is not set, go to next step.
  3. Turn ignition on. Read and record FAIL RECORDS data for DTC P0446. Clear DTCs. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays zero in. H20, go to next step. If scan tool does not display zero in. H2O, repair faulty fuel tank sensor circuit.
  4. Zero pressure and vacuum gauges on EVAP Pressure/Purge Cart (J41413). Reinstall fuel cap. Using scan tool, command EVAP vent solenoid ON (closed). Connect EVAP pressure/purge cart to EVAP service port. Using EVAP pressure/purge cart, pressurize EVAP system to 5 in. H2O. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays 5 in. H2O, go to next step. If scan tool does not display 5 in. H2O, repair faulty fuel tank pressure sensor circuit.
  5. Maintain EVAP system pressure at 5 in. H2O. Using scan tool, command EVAP vent solenoid OFF (open). Monitor EVAP pressure/purge cart pressure gauge. If pressure decreases to zero in. H2O within 5 seconds, check for an intermittent problem, see DIAGNOSTIC AIDS. If pressure does not decrease as specified, go to next step.
  6. Disconnect vent hose, marked "AIR", from EVAP canister. Switch EVAP pressure/purge cart rotary switch to PURGE. Start engine and allow it to reach operating temperature. Monitor vacuum gauge for 5 seconds while holding engine speed at 2500 RPM. If vacuum remains at less than 30 in. H2O, go to next step. If vacuum does not remain as specified, go to step 9).
  7. Check if vent hose is between EVAP canister and EVAP solenoid is kinked, pinched or blocked. If a problem is found, repair as necessary and go to step 10). If no problem is found, go to next step.
  8. Replace EVAP vent solenoid and go to step 10).
  9. Replace EVAP canister and go to next step.
  10. Using scan tool, command EVAP vent solenoid ON (closed). With EVAP pressure/purge cart connected to EVAP service port, pressurize EVAP system to 5 in. H2O. Switch EVAP pressure/purge cart rotary switch to HOLD. Using scan tool, command EVAP vent solenoid OFF (open). If pressure decreases to zero in. H2O within 5 seconds, repair is complete. If pressure does not decrease as specified, return to step 3).
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