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Home >> Mazda >> 2003 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 26 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0171: Fuel Trim, Too Lean >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

WARNING: This page is about a different car, the 2002 Mazda Protege5 and 2002 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn ignition off. Connect scan tool to DLC-2. Turn ignition on, engine off. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check service bulletins for repair information related to this DTC. If repair information is not available, go to next step. If repair information is available, perform diagnosis and repair as necessary. After repair, go to step  19.
  2. Turn ignition off, then start engine. Using scan tool, check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If no other DTCs are present and no driveability problems are present, go to next step. If a driveability problem is present, go to step  7. If a misfire DTC is present, go to step  7. If any other DTCs are present, go to appropriate DTC trouble shooting procedure.
  3. Check if DTC P0171 is present in FREEZE FRAME DATA. If DTC P0171 is present, go to next step. If any other DTC is present that triggered freeze frame data, go to appropriate DTC trouble shooting procedure.
  4. Start engine and allow to idle. Using scan tool, access ECT, MAF, TP and VS PIDs. Ensure all PID data is within specification. See PIN VOLTAGE CHARTS . If all PID data is within specification, go to next step. If any PID data is not within specification, diagnose and repair suspect sensor or related wire harness as necessary. Refer to WIRING DIAGRAMS article. After repair, go to step  19.
  5. Inspect FREEZE FRAME PID data from step  4 while operating vehicle under freeze frame data conditions. If there is no input signal which causes drastic changes, go to next step. If any input signal causes drastic changes, diagnose and repair suspect sensor or related wire harness as necessary. Refer to SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE, PROTEGE5 & 626 article. After repair, go to step  19.
  6. Using scan tool, access O2S11 PID. O2S11 PID value should be more than .45 volt during acceleration (rich condition) and less than .45 volt during deceleration (lean condition). If PID reading is okay, check for vacuum leaks due to cracked, damaged or loose components between air cleaner and throttle body, throttle body and dynamic chamber, and between dynamic chamber and intake manifold. Also check for cracked, damaged or loose vacuum hoses. Repair as necessary. After repair, go to step  19. If PID reading is not as specified, check for exhaust leaks up stream of front HO2S. If no exhaust leaks are present, replace front HO2S. Repair as necessary. After repair, go to step  19.
  7. Start engine. Using scan tool, access MAF PID. Depress accelerator pedal to Wide Open Throttle (WOT) and release to race engine. MAF PID voltage reading should respond quickly to changes in engine RPM. If MAF PID response is as specified, go to next step. If MAF PID response is not as specified, replace Mass Airflow (MAF) sensor. After repair, go to step  19.
  8. Inspect intake-air system and all vacuum lines for leaks. If no leaks are found, go to next step. If any leak is found, repair as necessary. After repair, go to step  19.
    NOTE: During next procedure, if engine will not start, inspect fuel line pressure with ignition on.
  9. Turn ignition off. Check fuel line pressure with engine running. See FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. Fuel line pressure should be 30-36 psi (2.1-2.6 kg/cm2 ). If fuel pressure is more than specified, go to next step. If fuel pressure is less than specified, go to step  11. If fuel line pressure is as specified, go to step  13.
  10. Disconnect vacuum hose from fuel pressure regulator. If vacuum is present at end of hose, check fuel pump maximum pressure. See FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. Also check fuel return hose for clogging. If any problem is found, repair or replace suspected parts. If no problem is found, replace fuel pressure regulator. Repair as necessary. After repair, go to step  19. If no vacuum is present at hose, check vacuum hose routing. If vacuum hoses are okay, replace Pressure Regulator Control (PRC) solenoid valve. Repair as necessary. After repair, go to step  19.
  11. Check fuel pump maximum pressure. See FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If maximum pressure is 64-92 psi (4.5-6.5 kg/cm2 ), go to next step. If maximum pressure is not as specified, check for open or poor connection in fuel pump circuit. If fuel pump circuit is okay, replace fuel pump. After repair, go to step  19.
    NOTE: Fuel delivery pipe may also be referred to as fuel rail.
  12. Check for leaks in fuel system from fuel pump to fuel delivery pipe. If any leaks are found, replace leaking fuel line. After repair, go to step  19. If no leaks are found, check for restriction or clogging at high pressure fuel filter. If restriction is present, replace high pressure fuel filter. Check for foreign material or staining inside low pressure fuel filter. If foreign material is found in low pressure fuel filter, clean fuel tank and low pressure fuel filter. If fuel filters and fuel tank are okay, replace fuel pressure regulator. Repair as necessary. After repair, go to step  19.
  13. Start engine and allow to idle. Check ignition coil operation at each cylinder with timing light. If timing light does not flash at each cylinder, go to next step. If timing light flashes at all cylinders, go to step  17.
  14. Turn ignition off. Check high-tension leads for corrosion, poor connection and damage. If high-tension leads are okay, go to next step. If problem is found with high-tension leads, replace high-tension leads. After repair, go to step  19.
  15. Disconnect ignition coil 3-pin harness connector. Turn ignition on, engine off. Measure voltage between ground and ignition coil 3-pin harness connector terminal "A" (Black/Blue wire). If battery voltage is present, go to next step. If battery voltage is not present, repair open circuit in Black/Blue wire between ignition switch terminal "IG1 and ignition coil 3-pin harness connector terminal "A". See WIRING DIAGRAMS article. After repair, go to step  19.
  16. Check ignition coil resistance. See EXCEPT B2300, B3000, B4000 & TRIBUTE under IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If coil resistance is okay, go to next step. If coil resistance is not as specified, replace faulty ignition coil. After repair, go to step  19.
  17. Check engine compression. See MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. Engine compression should be a minimum of 119 psi (8.4 kg/cm2 ) at 300 RPM with a maximum variation of 28 psi (2 kg/cm2 ). If compression is as specified, go to next step. If compression is not as specified, repair as necessary. After repair, go to step  19.
  18. Check fuel injector operation at suspect cylinder(s). See FUEL CONTROL under FUEL SYSTEM in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE, PROTEGE5 & 626 article. If no problem is found, go to next step. If fuel injector is faulty, replace suspect fuel injector(s). After repair, go to next step.
  19. Reconnect all connectors. Turn ignition on, engine off. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Perform DRIVE MODE 1 - PCM ADAPTIVE MEMORY , DRIVE MODE 2 - EGR MONITOR REPAIR VERIFICATION  and DRIVE MODE 3 - HO2S, HO2S HEATER & TWC REPAIR VERIFICATION  under SELF-DIAGNOSTIC SYSTEM. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If DTC P0171 is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article. After repair, go to next step. If same DTC P0171 is not present, go to next step.
  20. Cycle ignition switch from off to on. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. 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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