Diagnostic Aids

The system will become lean if a fuel injector is not supplying enough fuel.
A lean condition could be present during high fuel demand due to a fuel pump that does not deliver enough fuel, a plugged fuel filter, or a restricted fuel pipe.
Test for fuel contamination. Water or alcohol can effect fuel trim. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (W/O Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (W/Special Tool) .
Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Intermittent Conditions .

DTC P0171

Step	Action	Values	Yes	No
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module (ECM) Connector End Views or Engine Controls Connector End Views
1	Did you perform the Diagnostic System Check - Engine Controls?	-	Go to Step 2	Go to Diagnostic System Check - Engine Controls
2	Are any DTCs other than P0171 also set?	-	Go to Diagnostic Trouble Code (DTC) List	Go to Step 3
3	Start the engine. Allow the engine to reach the normal operating temperature and enter Closed Loop. Observe the Long Term FT parameter with a scan tool. Is the Long Term FT more than the specified value?	30 %	Go to Step 4	Go to Diagnostic Aids
4	Operate the engine at idle. Observe the heated oxygen sensor (HO2S) 1 voltage parameter with a scan tool. Is the voltage within the specified range and fluctuating?	200-800 mV	Go to Step 5	Go to Step 6
5	Turn OFF the engine. Inspect for the following conditions: Splits, kinks, or improper connections at the vacuum hoses - Refer to Emission Hose Routing Diagram . Low fuel pressure - Refer to Fuel System Diagnosis . Lean fuel injectors - Refer to Fuel Injector Coil Test . Fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (W/O Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (W/Special Tool) . Did you find and correct the condition?	-	Go to Step 9	Go to Step 8
6	Turn OFF the engine. Turn ON the ignition, with the engine OFF. Observe the manifold absolute pressure (MAP) sensor pressure parameter with a scan tool. Compare the MAP sensor parameter on the scan tool to the barometric pressure table. Refer to ALTITUDE VS BAROMETRIC PRESSURE The MAP sensor pressure should be within the range specified for your altitude. Does the MAP parameter indicate the correct barometric pressure?	-	Go to Step 7	Go to DTC P0106
7	Turn OFF the engine. Inspect for the following conditions: The correct installation of the HO2S The electrical connectors and wires are secured and not contacting the exhaust system. An open or a short to ground in the HO2S signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	-	Go to Step 9	Go to Fuel System Diagnosis
8	Operate the engine at idle. Inspect for the following conditions: Missing, loose, or leaking exhaust components Vacuum leaks at the intake manifold, throttle body, and injector O-rings Leaks at the air intake ducts Leaking crankcase ventilation system Did you find and correct the condition?	-	Go to Step 9	Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.6L (L91)
9	Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	-	Go to Step 2	Go to Step 10
10	Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed?	-	Go to Diagnostic Trouble Code (DTC) List	System OK