Diagnostic Aids

WARNING: This page is about a different variant/trim than selected.

A malfunctioning MAF sensor can cause a rich condition and set this DTC.
If an intermittent condition is suspected, refer to Testing for Intermittent Conditions and Poor Connections .
This DTC may set due to poor idle characteristics. A possible cause may be uncontrolled fueling due to an open or high resistance in the HO2S 1 low signal circuit. Before replacing any component, ensure that this condition does not exist.

DTC P0172

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 P0172 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 the normal operating temperature in Closed Loop. Observe the Long Term FT parameter. Does the scan tool indicate that the Long Term fuel trim is less than the specified value?	-19.5%	Go to Step 4	Go to Diagnostic Aids
4	Operate the engine at idle. Observe HO2S 1 parameter with a scan tool. Does the scan tool indicate that the heated oxygen sensor (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: The inlet screen of the mass airflow (MAF) sensor for blockage-Refer to Mass Airflow Sensor Replacement . Vacuum hoses for splits, kinks, and proper connections-Refer to Emission Hose Routing Diagram . The air intake duct for being collapsed or restricted-Refer to Air Cleaner Inlet Duct Replacement . The air filter for being dirty or restricted-Refer to Air Cleaner Element Replacement . Objects blocking the throttle body-Refer to Throttle Body Assembly Replacement . Did you find and correct the condition?	-	Go to Step 10	Go to Step 9
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 Visually and physically inspect the following items: The 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 for 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 Step 9
9	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 Fuel System Diagnosis
10	Inspect for the following: Excessive fuel in the crankcase Saturated evaporative canister, stuck purge valve or fuel cap not sealing Excessive fuel pressure-Refer to Fuel System Diagnosis . Properly functioning fuel injectors-Refer to Fuel Injector Diagnosis (w/J39021 or w/Tech 2) or Fuel Injector Diagnosis (w/CH47976) . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel 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