Diagnostic Aids

The system may become lean if an injector is not suppling enough fuel.
Excessive resistance in the fuel injector control and/or the ignition 1 voltage circuits may cause the following symptoms:
- A lean condition
- Misfire
- Rough idle
  Refer to DTC P0201-P0208
A lean condition could be present during high fuel demand.
Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Testing for Intermittent Conditions and Poor Connections .

DTC P0171

Step	Action	Values	Yes	No
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle
2	Are any DTCs other than DTC P0171 also set?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle	Go to Step 3
3	Install the scan tool. Start and idle the engine at the normal operating temperature in Closed Loop. Record the long term fuel trim. Turn OFF the engine. Turn ON the ignition, with the engine OFF. Review the Freeze Frame/Failure Records and record the displayed data for this DTC. Does the scan tool indicate that the long term fuel trim is greater than the specified value?	24%	Go to Step 4	Go to Diagnostic Aids
4	Operate the engine at idle. Observe the HO2S parameters with a scan tool. Does the scan tool indicate that the parameter is within the specified range and fluctuating?	200-800 mV	Go to Step 5	Go to Step 6
5	Turn OFF the engine. Visually and physically inspect the following items: The vacuum hoses for splits, kinks, and proper connections-Refer to Emission Hose Routing Diagram . Ensure that the vehicle has sufficient fuel in tank. If fuel pressure is too low, this DTC may set. Refer to Fuel System Diagnosis . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool)Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) . Any lean fuel injectors-Refer to Fuel Injector Balance Test with Tech 2 . Did you find and correct the condition?	-	Go to Step 8	Go to Step 7
6	Turn OFF the engine. Inspect the heated oxygen sensor (HO2S) for proper installation. Verify the electrical connectors and the wires are secure, and not contacting the exhaust system. Test for continuity between the HO2S signal circuit and the low reference circuit. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor (HO2S) Wiring Repairs . Did you find and correct the condition?	-	Go to Step 8	Go to Fuel System Diagnosis
7	Operate the engine at idle. Inspect for any missing, loose, or leaking exhaust components forward of the HO2S. Inspect for vacuum leaks at the intake manifold, throttle body, and injector O-rings. Inspect the air induction system and the air intake ducts for leaks. Inspect the secondary air injection (AIR) system for leaks, improper air delivery, and for the shut-off valves not closing. Inspect the crankcase ventilation system for leaks. Refer to Crankcase Ventilation System Inspection/Diagnosis . Inspect the evaporative emission (EVAP) lines and components for damage or blockage. Refer to Evaporative Emissions (EVAP) Hose Routing Diagram . Did you find and correct the condition?	-	Go to Step 8	Go to Symptoms - Engine Mechanical
8	IMPORTANT: After repairs, Reset the Long Term Fuel Trim with the scan tool Fuel Trim Reset function. Turn ON the ignition, with the engine OFF. 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 9
9	Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle	System OK