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Home >> Pontiac >> 2001 >> Aztek Base, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P0171: Fuel Trim System - Lean >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
  2. Ensure no other DTCs are set. Start and operate engine at idle and at normal operating temperature, and in closed-loop. Using scan tool, record the LONG TERM FUEL TRIM data. Turn engine off. Turn ignition on, with engine off. Review FREEZE FRAME/FAILURE RECORDS and record displayed data for this DTC. If scan tool indicates that Long Term Fuel Trim is greater than 23 percent, go to next step. If Long Term Fuel Trim is not greater than 23 percent, see DIAGNOSTIC AIDS .
  3. Start and operate engine at idle. Using scan tool, observe HO2S parameters. If scan tool indicates that values are within 200-800 millivolts and fluctuating, go to next step. If values are not within 200-800 millivolts or not fluctuating, go to step  5.
  4. Turn engine off. Check vacuum hoses for splits, kinks, and proper connections. Ensure vehicle has sufficient fuel in tank. If fuel pressure is too low, this DTC may set. Repair as necessary. After repairs, go to step  7. If no problem is found, go to step  6.
  5. Turn engine off. Check HO2S for proper installation. Ensure harness connectors and wires are secured and not contacting exhaust system. Check for HO2S 2 circuits for short to each other. Repair as necessary. After repairs, go to step  7. If no problem is found, diagnose fuel system. See BASIC FUEL SYSTEM CHECKS (GASOLINE) in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  6. Operate engine at idle. Check for missing, loose or leaking exhaust components forward of HO2S. Check for vacuum leaks at intake manifold, throttle body or injector "O" rings. Check air induction system and air intake ducts for leaks. Check AIR system for leaks, improper air delivery or shut-off valve not closing. Check crankcase ventilation system for leaks. Repair as necessary. After repairs, go to next step. If no problem is found, diagnose for engine mechanical problem.
  7. After repairs, use scan tool to reset the Long Term Fuel Trim. After resetting fuel trim, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running this DTC. See CODE ENABLE CRITERIA . If DTC runs and passes, go to next step. If DTC resets, go to step  2.
  8. Using scan tool, observe the stored information and CAPTURE INFO. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are displayed, system is okay.
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