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DTC P0171: Fuel System Lean

NOTE: If any DTCs besides DTC P0171 and P0172 are set, diagnose them first.
  1. Connect scan tool to Data Link Connector (DLC). Start engine and allow it to reach normal operating temperature. Increase engine speed to 2000 RPM and release to idle. Repeat 5-6 times continuously while monitoring HO2S No. 1 parameter on scan tool. If display reading varies from less than 0.3 volt to greater than 0.6 volt, go to next step. If display reading is not a specified, follow procedures in DTC P0134  .
  2. Install fuel pressure gauge. Check fuel pressure at specified conditions. See FUEL PUMP PERFORMANCE table below. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to TEST B-3 under CIRCUIT TESTS in BASIC TESTING article.
    FUEL PUMP PERFORMANCE

    KOEO psi (kg/cm2 ) (1) Engine @ Idle psi (kg/cm2 )
    22.7-29.9 (1.6-2.1) 12.8-20.0 (0.9-1.4)
    (1) Key on, engine off.
  3. Check fuel injector and fuel system circuit. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. Repair as necessary. Retest system. If fuel system is okay, go to next step.
  4. Ensure engine is cool. Disconnect purge hose from EVAP canister. Start engine. Place a finger over end of disconnected hose. If no vacuum is present, go to next step. If vacuum is present, check EVAP control system. See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article. Repair as necessary. Retest system.
  5. Check MAP sensor performance. See DTC P0106  , step 4). Repair as necessary. If MAP sensor performance is okay, go to next step.
  6. Check ECT sensor performance. See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article. Repair as necessary. If ECT sensor performance is okay, go to next step.
  7. Check IAT sensor performance. See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article. Repair as necessary. If IAT sensor performance is okay, go to next step.
  8. Check TP sensor performance. Follow procedures in step 3) of DTC P0121  . Repair as necessary. Retest system. If TP sensor performance is okay, go to next step.
  9. Check CTP switch operation. See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article. Repair as necessary. If CTP switch operation is okay, go to next step.
  10. Disconnect hose from PCV valve. Start engine and let idle. Check for vacuum at PCV valve. If vacuum is not present, remove PCV valve from intake manifold. If engine runs rough or stalls, replace PCV valve. If engine does not run rough or stall, check for restriction in PCV valve intake passage. Repair as necessary. If PCV system is okay, replace PCM. Retest system.
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