Diagnostic Aids

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.

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	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 Air Flow (MAF) 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 Intake 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 Visually and physically inspect the following items: The HO2S' for proper installation-Refer to Heated Oxygen Sensor Replacement - Position 1 and Heated Oxygen Sensor Replacement - Position 2 . 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 10	Go to Step 7
7	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 10	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 10	Go to Fuel System Diagnosis
9	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 Coil Test . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis . Did you find and correct the condition?	-	Go to Step 10	Go to Symptoms - Engine Mechanical
10	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 11
11	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