Test Description

The number below refers to the step number on the diagnostic table.

10: If the conditions were not corrected, a worn CAM, a worn intake, or exhaust valves or the engine mechanical failure may be at fault.

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	IMPORTANT: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system (TCS) indicators until any fuel trim fault are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators. Install the scan tool. Turn ON the ignition. Observe the Freeze Frame/Failure Records parameter with a scan tool and record the displayed data for this DTC. Start and idle the engine at normal operating temperature in the Closed Loop. Observe the Long Term FT parameter. Does the scan tool indicate that the Long Term fuel trim is more than the specified value?	18.8%	Go to Step 4	Go to Diagnostic Aids
4	Operate the engine at idle. Observe the heated oxygen sensor (HO2S) 1 sensor parameter with a scan tool. Does the scan tool indicate that the HO2S 1 voltage 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: Vacuum hoses for leaks, splits, kinks, and proper connections-Refer to Emission Hose Routing Diagram . Ensure that the vehicle has sufficient fuel in the tank. If the fuel pressure is too low, this DTC may set. Refer to Fuel System Diagnosis . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis . Any lean fuel injectors-Refer to Fuel Injector Diagnosis (w/J39021 or w/Tech 2) or Fuel Injector Diagnosis (w/CH47976) . Did you find and correct the condition?	-	Go to Step 11	Go to Step 10
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. Refer to Altitude Versus Barometric Pressure . The MAP sensor parameter should be within the range specified for your altitude. Does the MAP indicate the correct barometric pressure?	-	Go to Step 7	Go to Manifold Absolute Pressure Sensor Diagnosis
7	Turn OFF the engine. Inspect both HO2S for proper installation. Refer to Heated Oxygen Sensor 1 Replacement and Heated Oxygen Sensor 2 Replacement . Ensure that the electrical connectors and wires are secured and not contacting the exhaust system. Did you find and correct the condition?	-	Go to Step 11	Go to Step 8
8	Test the HO2S 1 low signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	-	Go to Step 11	Go to Step 9
9	Test for a short between the signal circuit and the low reference circuit or ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	-	Go to Step 11	Go to Fuel System Diagnosis
10	Operate the engine at idle. Inspect for the following conditions: Missing, loose, or leaking exhaust components, from the HO2S forward-Refer to Symptoms - Engine Exhaust . Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings Air induction system and the air ducts for leaks or for a missing air filter element-Refer to Air Cleaner Assembly Replacement and Air Cleaner Inlet Duct Replacement . Evaporative canister purge lines plugged or obstructed Properly functioning fuel injectors-Refer to Fuel Injector Diagnosis (w/J39021 or w/Tech 2) or Fuel Injector Diagnosis (w/CH47976) . Crankcase ventilation system for leaks-Refer to Crankcase Ventilation System Inspection/Diagnosis . Did you find and correct the condition?	-	Go to Step 11	Go to Symptoms - Engine Mechanical
11	IMPORTANT: Reset the Long Term Fuel Trim with the scan tool Fuel Trim Reset function after any of the above repairs. 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 in 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 12
12	In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the conditions for running and setting DTC P0420 and verify that P0420 runs and passes. Refer to DTC P0420 . Does the DTC run and pass?	-	Go to Step 13	Go to DTC P0420
13	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