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DTC P0171/16555 - System Too Lean (Bank 1)

NOTE: DTC is set when mixture is so lean that Heated Oxygen Sensor (HO2S) control cannot enrich mixture further.
  1. Start engine and let it idle. Inspect intake system for leaks between Mass Airflow (MAF) sensor and cylinder head. Repair as necessary. Erase DTC memory and test drive vehicle. See CLEARING DTCS in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets, go to next step. If an intake leak is not found, go to next step.
  2. Inspect secondary air injection system operation. Repair as necessary. Erase DTC memory and test drive vehicle. See CLEARING DTCS in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets, go to next step. If secondary air injection system is operating properly, go to next step.
  3. Check MAF sensor circuit. See DTC P0102/16486 and P0103/16487. Repair MAF sensor circuit as necessary. Erase DTC memory and test drive vehicle. See CLEARING DTCS in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets, go to next step. If MAF sensor circuit is operating properly, go to next step.
  4. Disconnect test box. Test drive vehicle for performance problems. If problem occurs only at full acceleration, replace fuel filter. Erase DTC memory and test drive vehicle. See CLEARING DTCS in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets or if other performance problem(s) exist, go to next step.
  5. If engine output is impaired at lower throttle openings or vehicle jerks at lower throttle openings, turn engine off. Check fuel injectors and circuit. See 2.0L or 2.8L under FUEL INJECTORS & CIRCUIT under FUEL SYSTEM in SYSTEM/COMPONENT TESTS - GASOLINE article. Repair fuel injectors and circuit as necessary. Erase DTC memory and test drive vehicle. See CLEARING DTCS  in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets, go to next step. If fuel injectors and circuit are operating properly, go to next step.
  6. Inspect fuel injectors for poor electronic connection or dirty/clogged injectors. Repair as necessary. Erase DTC memory and test drive vehicle. See CLEARING DTCS in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets, go to next step. If electronic connection and injectors are okay, go to next step.
  7. Replace pre-catalyst HO2S. Erase DTC memory and test drive vehicle. See CLEARING DTCS in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets, go to next step.
  8. Replace faulty ECM. Test drive vehicle. Recheck DTC memory and verify DTC does not reset. If DTC resets, repeat testing procedure.
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