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Diagnostic Procedures

  1. If QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed and any other DTCs are present, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS  . For DTCs P0171 or P0174, go to next step.
  2. Identify Trigger DTC For FREEZE FRAME DATA -  Read Freeze Frame Data. If DTC P0171 or P0174 data is stored in Freeze Frame Data, go to next step. If data from any other DTC is stored in Freeze Frame Data (meaning a more recent DTC is stored), repair other stored DTC(s) first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  .
  3. Verify Current Input Signal Status -  With KOER, access ECT V, MAF V, TP V and VSS PIDs. Observe signals. If signals are within specification during KOER, go to next step. If any signal is far out of specification during KOER, inspect suspect sensor and check for excessive resistance in related wiring harness. Repair or replace as necessary. After repair, go to step  14 .
  4. Verify Current Input Signal Status Under Trouble Condition -  Access ECT V, MAF V, TP V and VSS PIDs while simulating Freeze Frame Data conditions. Observe signals. If all signals are okay, go to next step. If any signal has drastic changes, inspect suspect sensor and related wiring harness. Repair or replace as necessary. After repair, go to step  14 .
  5. Verify Current Input Signal Status Of Front HO2S -  For DTC P0171, access O2S11 PID. For DTC P0174, access O2S21 PID. For either DTC, check PID under the following accelerator pedal conditions in Park:
    • Depress accelerator suddenly (rich condition). Voltage reading should be more than 0.45 volt.
    • Release accelerator suddenly (lean condition). Voltage reading should be less than 0.45 volt.
    If voltage reading is okay, inspect air intake system for leaks. Check from air cleaner to throttle body, from throttle body to dynamic chamber, from dynamic chamber to intake manifold, and vacuum hoses. Repair as necessary. After repair, go to step  14 . If no leaks are present, inspect exhaust system for leaks. Repair as necessary. If no exhaust leaks are present, replace faulty HO2S. After repair, go to step  14 .
  6. Inspect MAF V PID -  With KOER, access MAF V PID. Observe voltage. Verify voltage changes quickly with engine RPM. If voltage reading is okay, go to next step. If voltage reading is not okay, replace faulty MAF/IAT sensor. After repair, go to step  14 .
  7. Inspect For Excessive Air Suction Of Intake Air System -  Visually inspect air intake system for damaged or loose parts. If no problem is found, go to next step. If a problem is found, repair or replace as necessary. After repair, go to step  14 .
  8. Inspect Fuel Line Pressure -  Turn ignition off. Connect a fuel pressure gauge to vehicle. With KOER fuel pressure should be 30-65 psi (207-448 kPa). If fuel pressure reading is within specification, go to step  12 . If fuel pressure reading is not within specification, go to next step.
  9. Inspect Fuel Pump Circuit -  Turn ignition off. Inspect fuel pump circuit for open or poor connection. If circuit is okay, go to next step. If circuit is not okay, repair or replace as necessary. After repair, go to step  14 .
  10. Inspect Fuel Line From Fuel Pump To Fuel Delivery Line -  Visually inspect fuel lines for damage or leakage. If any fuel leaks are found, replace fuel line. After repair, go to step  14 . If no leaks are found, go to next step.
    11. NOTE: Low pressure side fuel filter is located at bottom of fuel pump module inside fuel tank.
    Fig 1: Identifying High Pressure Side Fuel Filter
    G00193648Courtesy of MAZDA MOTORS CORP.
  11. Inspect Fuel Filter -  Inspect fuel filters. If high pressure side fuel filter is plugged, replace faulty fuel filter. See Fig 1 . After repair, go to step  14 . If low pressure side fuel filter is stained or has foreign material, clean fuel filter and tank. After repair, go to step  14 . If fuel filters are okay, replace fuel pump. After repair, go to step  14 .
  12. Inspect Engine Compression -  Inspect engine compression. See MECHANICAL INSPECTION under PRELIMINARY INSPECTIONS & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. If engine compression is okay, go to next step. If engine compression is not okay, repair engine as necessary.
  13. Inspect Fuel Injector Operation -  Remove injector from suspected bank. Swap injector with an injector from other bank. With KOER, check fuel trim. If injector bank which has suspect injector now indicates lean, turn ignition off. Replace faulty fuel injector. After repair, go to next step. If injector bank which has suspect injector does not indicate lean, go to next step.
  14. Drive Cycle -  Reconnect all electrical connectors. Using scan tool, clear DTC memory. Perform HO2S MONITOR REPAIR VERIFICATION DRIVE CYCLE  or FUEL OR MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE  in MONITOR REPAIR VERIFICATION DRIVE CYCLES under DRIVE CYCLE PROCEDURES. Using scan tool, retrieve DTCs. If same DTC is not present, go to next step. If same DTC is present, replace faulty PCM. After repair, go to next step.
  15. Verify Trouble Shooting Of DTCs Completed -  Make sure all electrical connectors are reconnected. Clear DTCs from PCM memory using scan tool. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If any DTC is present, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no DTCs are present, test is complete.
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