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Home >> Mazda >> 2003 >> MPV ES >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0171 Or DTC P0174 >> Diagnostic Procedures
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Diagnostic Procedures

  1. Record freeze frame data. Check for service bulletins and on-line information. Repair as necessary. After repair, go to next step.
  2. Verify Related Pending Code Or Stored DTCs -  Turn ignition off, then on (engine off). Verify stored DTCs. If misfire DTC is present, go to step  7. If any other DTC is present, repair that DTC first. Refer to DIAGNOSTIC TROUBLE CODE IDENTIFICATION . If no other DTCs are present, and there are no driveability problems, go to next step. If no other DTCs are present, and there are driveability problems, go to step  7.
  3. Identify Trigger DTC For Freeze Frame Data -  Verify if DTC P0171 or P0174 is present in FREEZE FRAME DATA. If DTC is present, go to next step. If DTCs are not present in FREEZE FRAME DATA, go to appropriate diagnostic procedure for DTC that is on FREEZE FRAME DATA. Refer to DIAGNOSTIC TROUBLE CODE IDENTIFICATION .
  4. Verify Current Input Signal Status (Ignition To On/Idle) -  Using scan tool, access MAF, ECT, TP and VSS PIDs. Compare readings with specifications. See PIN VOLTAGE/PID VALUE CHARTS in PIN VOLTAGE CHARTS article. If all data is within specification, go to next step. If any data is not within specification with ignition on and engine runs, inspect suspect sensor and related wire harness for excessive resistance. Refer to appropriate test in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. Repair as necessary. After repair, go to step  18.
  5. Verify Current Input Signal Status Under Trouble Condition -  Referring to FREEZE FRAME DATA, operate vehicle under same conditions as when DTC was set. Check PID data for MAF, ECT, TP and VSS. Compare readings with specifications. See PIN VOLTAGE/PID VALUE CHARTS in PIN VOLTAGE CHARTS article. If all data is within specification, go to next step. If any input causes drastic changes, inspect suspected sensor and related wire harnesses. Refer to appropriate test in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. Repair or replace as necessary. After repair, go to step  18.
  6. Verify Current Input Signal Status Of Front HO2S (Right Side, Left Side) -  Using scan tool, access O2S11 (P0171) or O2S21 (P0174) PID. Depress accelerator pedal to WOT and release to race engine. If PID reading is more than .45 volt when accelerator pedal is suddenly depressed (rich condition) and less than .45 volt just after accelerator pedal is released (lean condition), check for any air leaks caused by cracks, damaged or loose parts between:
    • Air cleaner and throttle body.
    • Throttle body and dynamic chamber.
    • Dynamic chamber and intake manifold.
    • Vacuum hoses.

    Repair or replace faulty parts as necessary. After repair, go to step  18. If PID reading is not as specified, check for exhaust leaks between exhaust manifold and front HO2S. If problem is found, repair as necessary. If no leaks are found, replace front HO2S. After repair, go to step  18.

  7. Inspect MAF PID -  Start engine. Using scan tool, access MAF PID. Depress accelerator pedal to WOT and release to race engine. Ensure MAF PID reading responds quickly according to RPM changes. If MAF PID reading responds as specified, go to next step. If MAF PID reading does not respond as specified, replace Mass Airflow (MAF) sensor. After repair, go to step  18.
  8. Inspect For Excessive Air Suction Of Intake Air System -  Check for air leaks (loose, damaged or cracked hoses on intake air system. If no leaks are found, go to next step. If any leaks are found, repair or replace faulty components as necessary. After repair, go to step  18.
    NOTE: For following procedure, if engine won't start, check fuel pressure with ignition on.
  9. Inspect Fuel Line Pressure -  Check fuel line pressure with engine running. See FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel line pressure is 61-66 psi (420-460 kPa), go to step  12. If fuel line pressure is excessively low, go to next step. If fuel line pressure is excessively high, inspect fuel pump maximum pressure and fuel return hose for clogging. Repair as necessary. If no problem is found, replace fuel pressure regulator. After repair, go to step  18.
  10. Inspect Fuel Pump Maximum Pressure -  Check fuel pump maximum pressure. See FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel pump maximum pressure is 86-116 psi (590-800 kPa), go to next step. If fuel pump maximum pressure is not as specified, check fuel pump circuit for open or poor connection. Repair as necessary. After repair, go to step  18. If no problem is found, replace fuel pump. After repair, go to step  18.
  11. Inspect Fuel Line From Fuel Pump To Fuel Delivery Pipe -  Check fuel system for any fuel leaks. If any leaks are present, replace suspect fuel line. After repair, go to step  18. If leaks are not present, check fuel filters foreign material, restriction or clogging. If high pressure filter is clogged or restricted, replace high pressure fuel filter. If foreign material or stain is found in low pressure filter, clean fuel tank and filter. If no problem is found, replace fuel pressure regulator. Repair or replace as necessary. After repair, go to step  18.
  12. Inspect Fuel Injector Operation -  Remove fuel injector from suspect bank. Swap suspect injector with injector from other bank. Start engine. If fuel trim system lean DTC is not for bank with suspect injector, go to next step. If fuel trim system lean DTC is for bank with suspect injector, replace fuel injector. After repair, go to step  18.
  13. Check Ignition Coil Operation With Spark Tester -  Using spark tester, check for Bluish spark at each ignition coil. If Bluish spark is not present at all cylinders, go to next step. If all cylinders show a Bluish spark, go to step  17.
  14. Check Secondary Ignition Coil Terminal Of No Spark Cylinder -  Turn ignition off. Check ignition coil for incorrect installation, damage or corrosion at ignition terminals, open lead and damaged cover. If no problem is found, go to next step. If any problem is found, replace faulty ignition coil. After repair, go to step  18.
  15. Inspect Power Supply Terminal At Ignition Coil Connector -  Disconnect ignition coil harness connector. Turn ignition on, engine off. Check voltage between ground and ignition coil harness connector terminal "A" (White/Violet wire). See appropriate wiring diagram under ENGINE PERFORMANCE in WIRING DIAGRAMS. If battery voltage is present, go to next step. If battery voltage is not present, repair open in White/Violet wire between ignition coil harness connector terminal "A" and ignition switch terminal "IG 1". Go to step  18.
  16. Inspect Ignition Coil Resistance -  Check ignition coil resistance. See IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If coil resistance is okay, go to next step. If ignition coil is faulty, replace ignition coil and go to step  18.
  17. Inspect Engine Compression -  Check engine compression. See MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. If compression is okay, go to next step. If compression is low, overhaul engine. Refer to appropriate MECHANICAL article in ENGINES. After repair, go to next step.
  18. Verify Trouble Shooting Of DTC P0171 Or P0174 Completed -  Reconnect all connectors. Using scan tool, clear DTC. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine and perform MODE 1 - PCM ADAPTIVE MEMORY PRODUCE DRIVE MODE  and MODE 3 - HO2S HEATER, HO2S & TWC REPAIR VERIFICATION DRIVE MODE  under DRIVE MODES. Stop vehicle and access PID/DATA MONITOR RECORDED to inspect DRIVE MODE completion status. Ensure Readiness Function Check (RFC) flag changes to OFF for FUEL SYASTEM MONITIOR. If RFC flag does not change, run DRIVE MODEs again. Access PENDING CODE. If PENDING CODE P0171 is present, replace PCM. After repair, go to next step. If DTC is not present, go to next step.
  19. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If no other DTCs are present, testing is complete. If any other DTC is present, go to applicable test and repair.
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