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DTC P0171 Fuel Trim System Too Lean: Troubleshooting

TROUBLESHOOTING CHART

Step Action Value(s) Yes No
1 Perform an On-Board Diagnostic (OBD II) System Check.
Was the check performed?		 - Go to Step 2 Go to "ON-BOARD DIAGNOSTIC (OBD II) SYSTEM CHECK :"
2
  1. Install the scan tool to the Data Link Connector (DLC).
  2. Turn the ignition ON.

Are any component related Diagnostic Trouble Codes (DTCs) set?		 - Go to APPLICABLE DTC TABLE  Go to Step 3
3 With the engine running, operate the vehicle until the LOOP STATUS indicates closed.
Is the Long Term Fuel Trim value below the specified value?		 25% Go to Step 4 Go to Step 5
4
  1. Turn the ignition switch ON, with the engine OFF.
  2. Review the Freeze Frame data and note the parameters.
  3. Operate the vehicle within the Freeze Frame conditions and Conditions for Setting The DTC as noted.

Does the Long Term Fuel Trim value go below the specified value while operating under the specified conditions?		 25% Go to Step 16 Go to Step 5
5 Visually/physically check the following items:
  • Vacuum hoses for splits, kinks and improper connections.
  • Crankcase ventilation oil/air separator for proper installation.
  • Exhaust system for corrosion, leaks, loose or missing hardware.
  • Oxygen sensor 1 (O2S1) is installed securely and the pigtail harness is not contacting exhaust manifold or engine.
  • Fuel for excessive water, alcohol, or other contaminants.
  • Engine Control Module (ECM) and sensor grounds are clean, tight, and in their proper locations.

Do any of the above checks isolate a condition requiring repair?		 - Go to Step 7 Go to Step 6
6
  1. Disconnect the Manifold Absolute Pressure (MAP) sensor electrical connector.
  2. Operate the vehicle in Closed Loop while monitoring the Long Term Fuel Trim value.

Is the Long Term Fuel Trim value below the specified value?		 25% Go to Step 15 Go to Step 9
7
  1. Repair the malfunction found in Step 5.
  2. Recheck the Long Term Fuel Trim value while operating the engine.

Is the Long Term Fuel Trim value below the specified value?		 25% Go to Step 8 Go to Step 9
8 Lean condition is not present.
Does a driveability problem exist?		 - Go to "SYMPTOM DIAGNOSIS TABLE :" Go to Step 16
9
  1. Visually/physically inspect the following items for vacuum leaks:
    • Intake manifold.
    • Throttle body.
    • Injector O-rings.
  2. Repair any leaks found as necessary.

Is the repair complete?		 - Go to Step 16 Go to Step 10
10 Allow the engine to idle.
Are the Idle Air Control (IAC) counts above the specified value?		 5 Go to Step 11 Go to Step 12
11 Check the fuel for excessive water, alcohol, or other contaminants and correct the contaminated fuel condition if present.
Is the repair complete?		 - Go to Step 16 Go to Step 13
12 Check the IAC valve performance. Refer to "DTC P0506 IDLE SPEED RPM LOWER THAN DESIRED IDLE SPEED :" or "DTC P0507 IDLE SPEED RPM HIGHER THAN DESIRED IDLE SPEED :" and repair as necessary.
Is the repair complete?		 - Go to Step 16 Go to Step 13
13
  1. Connect a fuel pressure gauge to the fuel system.
  2. Turn the ignition OFF for at least 10 seconds.
  3. Turn the ignition ON, with the engine OFF. The fuel pump will run for approximately 2-3 seconds. It may be necessary to cycle the ignition switch ON more than once to obtain maximum fuel pressure.
  4. Note the fuel pressure with the fuel pump running. The pressure should be within the specified value. When the fuel pump stops, the pressure may vary slightly then hold steady.

Is the fuel pressure steady and does the fuel pressure hold?		 379~393 kPa (55~57 psi) Go to Step 14 Go to "FUEL SYSTEM DIAGNOSIS :"
14
  1. Start and idle the engine at normal operating temperature.
  2. The fuel pressure noted in the above step should drop by the indicated value.

Does the fuel pressure drop by the indicated value?		 21-69 kPa (3-10 psi) Go to "FUEL INJECTOR BALANCE TEST :" Go to "FUEL SYSTEM DIAGNOSIS :"
15 Replace the MAP sensor.
Is the action complete?		 - Go to Step 16 -
16
  1. Using the scan tool, clear the Diagnostic Trouble Codes (DTCs).
  2. Start the engine and idle at normal operating temperature.
  3. Operate the vehicle within the Conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic has run and passed?		 - Go to Step 17 Go to Step 2
17 Check if any additional DTCs are set.
Are any DTCs displayed that have not been diagnosed?		 - Go to APPLICABLE DTC TABLE  System OK
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