LEMON Manuals: Even more car manuals for everyone
Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 60 (Engine Controls [Self-Diagnostics 2.3L]) >> Diagnostic Tests >> DTC P0171: Fuel Trim System - Too Lean >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
  1. If FREEZE FRAME DATA has been recorded, go to next step. If FREEZE FRAME DATA has not been recorded, record FREEZE FRAME DATA. Go to next step.
  2. Verify Related Repair Information Availability -  Check for related Service Bulletins and/or on-line repair information availability. If any related repair information is available, perform repair or diagnosis according to available repair information. If vehicle is not repaired, go to next step. If related repair information is not available, go to next step.
  3. Verify Related Pending Code Or Stored DTCs -  Turn ignition off, then on (engine off). Verify related PENDING CODE or stored DTCs. If no other DTCs are present and driveability concern is not present, go to next step. If no other DTCs are present and a driveability concern is present, go to step  8. If misfire DTC is present, go to step  8. If any other DTC is present, go to appropriate DTC trouble shooting procedure. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  4. Identify Trigger DTC For FREEZE FRAME DATA -  If DTC P0171 is present on FREEZE FRAME DATA, go to next step. If any other DTC triggered FREEZE FRAME DATA, diagnose that DTC first. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  5. Verify Current Input Signal Status (Ignition Key To On/Idle) -  Access APP, APP1, APP2, ECT, MAF, TP and VSS PIDs using WDS or equivalent. Refer to PIN VOLTAGE & PID VALUE CHART INDEX in PIN VOLTAGE CHARTS article. If all PID values are okay with engine running, go to next step. If any signal is far out of specification when engine is running, check suspected sensor for fault and excessive resistance in related wiring harnesses. Repair or replace if necessary. After repair, go to step  19.
  6. Verify Current Input Signal Status Under Trouble Condition -  Inspect same PIDs as step  5 while simulating FREEZE FRAME DATA condition. Is there any input signal which causes drastic changes, inspect suspected sensor and related wiring harnesses. Repair or replace it. After repair, go to step  19.
    7. NOTE: During following step, engine -speed may change when rust penetrating agent is sprayed on the air suction area.
  7. Verify Current Input Signal Status Of Front HO2S -  Access O2S11 for P0171 PID using WDS or equivalent. Check PID under following accelerator pedal condition (in PARK (ATX) or NEUTRAL (MTX)).
    • More Than 0.55 volt  when accelerator pedal is suddenly depressed (rich condition)
    • Less Than 0.55 volt  just after release of accelerator pedal (lean condition)
    If PID readings are okay, check for air suction at following locations due to cracks, damaged and loosening parts:
    • From air cleaner to throttle body
    • From dynamic chamber to intake manifold
    • From throttle body to dynamic chamber
    • Vacuum hoses
    Repair or replace any faulty part. After repair, go to step  19. If PID readings are not okay, visually inspect for any gas leakage between exhaust manifold and front HO2S. If there is no leakage, replace front HO2S. After repair, go to step  19.
  8. Inspect MAF PID -  Start engine. Access MAF PID using WDS or equivalent. Verify that MAF PID changes quickly according to race engine RPM. If MAF PID response is okay, go to next step. If MAF PID response is incorrect, replace MAF/IAT sensor. After repair, go to step  19.
  9. Inspect For Excessive Air Suction Of Intake Air System -  Visually inspect for looseness, cracks or damaged hoses on intake air system. If malfunction is not present, go to next step. If any malfunction is present, repair as necessary. After repair, go to step  19.
    10. NOTE: If engine won't start, inspect fuel line pressure with ignition on.
  10. Inspect Fuel Line Pressure -  Turn ignition off. Inspect fuel line pressure while engine is running. Refer to FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel line pressure is okay, go to next step. If fuel line pressure is excessive, replace fuel pump. After repair, go to step  19.
  11. Inspect Fuel Line From Fuel Pump To Fuel Delivery Pipe -  Visually inspect fuel line for any leakage. If any fuel leakage is present, replace suspect fuel line. After repair, go to step  19. If fuel leakage is not present, check low-pressure side fuel filter for foreign materials or stain inside fuel filter. If foreign materials or stain is found inside fuel filter (low-pressure side), clean fuel tank and filter. If okay, replace fuel pump unit. After repair, go to step  19.
  12. Check Ignition Coil Operation & High-Tension Lead With Timing Light -  Verify blinking condition on each cylinder using timing light at idle. If any cylinder does not show blinking condition, go to next step. If all cylinders show blinking condition, go to step  16.
  13. Check High-Tension Leads Of No Blinking Cylinder -  Turn ignition off. Inspect high-tension leads for installation condition, corrosion on terminal, open lead and damaged cover. If condition of high-tension lead is okay, go to next step. If condition of any high tension lead is not okay, replace suspect high tension lead. After repair, go to step  19.
  14. Inspect Power Supply Terminal At Ignition Coil Connector -  Disconnect ignition coil 3-pin harness connector. Turn ignition on, engine off. Check voltage at ignition coil 3-pin harness connector terminal "B" (Black/White wire) and body ground. If battery voltage is present, go to next step. If battery voltage is not present, check for open circuit in Black/White wire between ignition coil 3-pin harness connector terminal "B" and ignition switch. Repair or replace wiring harness. After repair, go to step  19.
  15. Inspect Ignition Coil Resistance -  Check ignition coil resistance. Refer to COIL PACKS under IGNITION SYSTEM in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If ignition coil resistance reading is okay, go to next step. If ignition coil resistance reading is not okay, replace ignition coil. After repair, go to step  19.
    16. WARNING: Removing radiator cap when radiator is hot is dangerous. Scalding coolant and steam may shoot out and cause serious injury. When removing radiator cap, wrap a thick cloth around cap and turn it slowly.
    NOTE: If there are any small bubbles which make engine coolant white at filler opening, air is getting in from poor sealing to head gasket or other areas between combustion chamber and engine coolant passage. Large bubbles are normal since they are remaining air coming out from engine coolant passage.
  16. Inspect Sealing Of Engine Coolant Passage -  Remove radiator cap. Perform procedure to bleed air from engine coolant, then run engine at idle. If there are any small bubbles which make engine coolant white at filler opening, repair or replace faulty parts. After repair, go to next step. If small bubbles are not present, go to next step.
  17. Inspect Variable Valve Timing Control System Operation -  Inspect variable valve timing control system operation. Refer to VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION INSPECTION  under SYSTEM TESTS. If variable valve timing control system is working properly, go to next step. If variable valve timing control system is not working properly, repair or replace suspected part according to Variable Valve Timing Control System Inspection results. After repair, go to step  19.
  18. Inspect Fuel Injector Operation -  Remove fuel injector. Inspect fuel injector operation. FUEL CONTROL under FUEL SYSTEM in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If fuel injector is operating properly, go to next step. If fuel injector is not operating properly, replace fuel injector. After repair, go to next step.
  19. Verify Trouble Shooting Of DTC P0171 Completed -  Make sure to reconnect all disconnected connectors. Turn ignition on, engine off. Clear DTC from PCM memory using WDS or equivalent. Perform MODE 1 - PCM ADAPTIVE MEMORY PRODUCE DRIVE MODE  and MODE 3 - HO2S HEATER, HO2S & TWC REPAIR VERIFICATION DRIVE MODE  under DRIVE CYCLES. Stop vehicle and access ON BOARD READINESS TEST to inspect DRIVE MODE completion status. Verify FUEL_EVAL PID changes to YES. If not, run MODE 3 - HO2S HEATER, HO2S & TWC REPAIR VERIFICATION DRIVE MODE  under DRIVE CYCLES again. Access PENDING CODE. If PENDING CODE of same DTC is not present, go to next step. If PENDING CODE of same DTC is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION article. After repair, go to next step.
  20. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If any DTCs are present, go to appropriate DTC inspection. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are present, trouble shooting is complete.
scientia non olet · About LEMON Manuals