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Home >> Toyota >> 2001 >> Sienna CE >> Repair and Diagnosis >> External Pages >> Different car >> Section 125 (Engine Control System Self Diagnostics (2UZ-FE)) >> Diagnostic Tests >> DTC P0171, DTC P0172, DTC P0174 &/Or DTC P0174 >> Diagnosis & Repair

Diagnosis & Repair

WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check for any loose or defective PCV valve hose connections. PCV valve is located on top of passenger's side valve cover near front corner of valve cover. If PCV valve hose connections are okay, go to next step. If PCV valve hose connections are defective, repair or replace components as necessary.
  2. Ensure engine oil dipstick, oil filler cap, PCV system and all other air induction system components are intact and operating properly. If problem does not exist, go to next step. If problem exists, repair as necessary.
  3. Check operation of fuel injectors. See FUEL CONTROL under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. Fuel injector volume should be .20-.25 oz. (60-73 cc) within 15 seconds and difference in volume between each fuel injector should be less than .04 oz. (13 cc). Fuel injectors should not leak more than one drop every 12 minutes. If fuel injectors are okay, go to next step. If fuel injectors are defective, replace fuel injectors as necessary.
  4. Check Mass Airflow (MAF) meter and Engine Coolant Temperature (ECT) sensor. MAF meter may also be referred to as airflow meter. See AIRFLOW METER and ENGINE COOLANT TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - V6 & V8 article. If MAF meter and ECT sensor are okay, go to next step. If MAF meter or ECT sensor is defective, replace components as necessary. See MASS AIRFLOW METER and ENGINE COOLANT TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
  5. Check ignition system by performing spark test. See SPARK TEST under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - V6 & V8 article. If ignition system operates properly and spark exists, go to next step. If ignition system does not operate properly and spark does not exist, repair ignition system as necessary.
  6. Check fuel pressure. See FUEL PRESSURE under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - V6 & V8 article. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, repair fuel system as necessary.
  7. Check exhaust system for leaks. If no exhaust leak exists, go to next step. If exhaust leak exists, repair exhaust system as necessary.
  8. Connect Toyota hand-held tester or scan tool to Data Link Connector (DLC3) at driver's side of instrument panel. See Figure. Start engine and maintain engine speed at 2500 RPM for about 90 seconds to fully warm oxygen sensor. Allow engine to idle.
  9. Using hand-held tester or scan tool, monitor oxygen sensor output voltage with engine idling. Heated oxygen sensor output should alternate between less than 0.4 volt and more than 0.55 volt. If voltage is as specified, go to step  17. If voltage is not as specified, go to next step.
  10. Turn ignition off. Disconnect HO2S 4-pin connector. See Figure. Measure resistance between HO2S 4-pin connector terminals No. 2 (+B) and No. 1 (HT). Make note of measurement. Then, measure resistance between HO2S 4-pin connector terminals No. 1 (HT) and No. 4 (E1). See HO2S HEATER RESISTANCE SPECIFICATIONS . If resistance is within specification, go to next step. If resistance is not within specification, replace HO2S. See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
  11. Remove EFI relay from engine room relay box. See Figure. Test relay. See EFI RELAY under MODULES, MOTORS, RELAYS & SOLENOIDS in SYSTEM & COMPONENT TESTING article. If relay is bad, replace it. If relay is Ok, reinstall relay and go to next step.
  12. Remove glove box for access to ECM with electrical connectors still installed on ECM. See Figure. Check continuity between ECM and HO2S connectors at terminals listed below. See Figure and Figure .
    • ECM 35-pin connector E5 terminal No. 5 (HT1B) and HO2S (Bank 1 Sensor 2) terminal No. 1. Continuity should exist.
    • ECM 35-pin connector E5 terminal No. 29 (OX1B) and HO2S (Bank 1 Sensor 2) terminal No. 3. Continuity should exist.
    • ECM 35-pin connector E5 terminal No. 25 (HT2B) and HO2S (Bank 2 Sensor 2) terminal No. 1. Continuity should exist.
    • ECM 35-pin connector E5 terminal No. 21 (OX2B) and HO2S (Bank 2 Sensor 2) terminal No. 3. Continuity should exist.
    • ECM 35-pin connector E5 terminal No. 5 (HT1B) and body ground. Continuity should not exist.
    • ECM 35-pin connector E5 terminal No. 29 (OX1B) and body ground. Continuity should not exist.
    • ECM 35-pin connector E5 terminal No. 25 (HT2B) and body ground. Continuity should not exist.
    • ECM 35-pin connector E5 terminal No. 21 (OX2B) and body ground. Continuity should not exist.
  13. If continuity is as specified, replace HO2S. Then, go to next step. See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article. If continuity is not as specified, repair wiring as necessary. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article.
  14. Using Toyota hand-held tester or scan tool, clear DTCs from ECM. Perform test drive confirmation and then go to next step. See TEST DRIVE CONFIRMATION .
  15. Recheck for DTCs. If DTCs P0171, P0172, P0174 and/or P0175 does not exist, go to next step. If DTCs P0171, P0172, P0174 and/or P0175 exist, replace ECM. ECM is located behind glove box. See Figure. Then, perform test drive confirmation and then go to next step. See TEST DRIVE CONFIRMATION .
  16. Verify if vehicle ran out of fuel. If vehicle ran out of fuel, DTCs P0171, P0172, P0174 and/or P0175 was caused by the vehicle running out of fuel. If vehicle did not run out of fuel, problem is intermittent. Check for defective connections or intermittent problem in wiring. ECM is located behind glove box. See Figure.
  17. Using Toyota hand-held tester or scan tool, clear DTCs from ECM. Perform test drive confirmation and then go to next step. See TEST DRIVE CONFIRMATION .
  18. Recheck for DTCs. If DTCs P0171, P0172, P0174 and/or P0175 does not exist, go to step  20. If DTCs P0171, P0172, P0174 and/or P0175 exist, replace HO2S. See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article. Then, go to next step.
  19. Recheck for DTCs. If DTCs P0171, P0172, P0174 and/or P0175 does not exist, go to next step. If DTCs P0171, P0172, P0174 and/or P0175 exist, replace ECM. ECM is located behind glove box. See Figure. Then, perform test drive confirmation and then go to next step. See TEST DRIVE CONFIRMATION .
  20. Verify if vehicle ran out of fuel. If vehicle ran out of fuel, DTCs P0171, P0172, P0174 and/or P0175 was caused by the vehicle running out of fuel. If vehicle did not run out of fuel, problem is intermittent. Check for defective connections or intermittent problem in wiring. See Figure.
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