Diagnostic Procedures

1998 Oldsmobile Achieva 3.1 M, 4T40E/MN4SECTION Diagnostic Procedures
  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECKΒ  . Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. After performing OBD system check, go to next step.
  2. Check if DTC P1655 is also set. If DTC P1655 is set, diagnose using P1655 tests. If DTC is not set, go to next step.
  3. Turn ignition off. Remove fuel filler cap. Turn ignition on. Using scan tool, observe fuel tank pressure. If fuel tank pressure is zero in. H2O, go to next step. If fuel tank pressure is not zero in. H2O, diagnose evaporative system.
  4. Replace fuel filler cap. using scan tool, capture FAIL RECORD data for DTC P1441 and clear DTCs. Install EVAP pressure/purge diagnostic station to EVAP service port. Using scan tool, command EVAP vent solenoid on (closed). Attempt to pressurize EVAP system using diagnostic station. If pressure reading of 5 in. H2O can be achieved, go to next step. If pressure reading of 5 in. H2O cannot be achieved, go to step 6).
  5. Maintain tank pressure at 5 in. H2O. Observe fuel tank pressure on scan tool. If fuel tank pressure is 5 in. H2O, go to next step. If fuel tank pressure is not 5 in. H2O, go to next step.
  6. Check EVAP purge and source vacuum line routing and connections at EVAP purge solenoid. Repair as necessary. After repairs, go to step 9). If routing and connections are okay, go to next step.
  7. Remove engine vacuum source line from EVAP purge solenoid. Connect a hand-held vacuum pump to engine vacuum side of EVAP purge solenoid and apply 15 in. Hg vacuum. If solenoid holds vacuum, see DIAGNOSTIC AIDS. If solenoid does not hold vacuum, go to next step.
  8. Replace EVAP purge solenoid. After replacing solenoid, go to next step.
  9. Correct EVAP purge and source vacuum line routing and connections. After repairs, go to next step.
  10. Start engine. Remove fuel filler cap. Using scan tool's output tests function, select SEAL SYSTEM and activate. Replace fuel filler cap. Turn rotary switch on diagnostic station to PURGE position. Operate engine at idle while monitoring vacuum gauge on diagnostic station for a least 10 seconds. If vacuum holds at zero in. H2O while scan tool SEAL SYSTEM function is activated, system is okay. If vacuum does not hold at zero in. Hg, repeat step 3).
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.