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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 48 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0171 Or DTC P0174 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
  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. 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. 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. 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 should be more than 0.45 volts.
    • Release accelerator suddenly (lean condition). Voltage should be less than 0.45 volts.
    If voltage 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. 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. 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 is okay, go to next step. If voltage is not okay, replace faulty MAF sensor. Go to step  14 .

  7. Inspect For Excessive Air Suction Of Intake Air System

    Visually inspect air intake system for damage or loose parts. If a problem is found, repair or replace as necessary. Go to step  14 . If no problem is found, go to next step.

  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 is within specification, go to step  12 . If fuel pressure 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. Go to step  14 .

  10. Inspect Fuel Line From Fuel Pump To Fuel Delivery Line

    Visually inspect fuel lines for damage or leakage. If fuel lines are okay, repair or replace as necessary. Go to step  14 . If fuel lines are okay, 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. 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. 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. 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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