Diagnostic Aids

WARNING: This page is about a different car, the 2007 Isuzu i-370, 2007 GMC Canyon, and 2007 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.

The current cell can be observed using a scan tool.
A malfunctioning MAF sensor can cause a rich condition and set this DTC.
If an intermittent condition is suspected, refer to Intermittent Conditions .

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	IMPORTANT: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system (TCS) indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators. Are any DTCs other than DTC P0172 also set?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle	Go to Step 3
3	Turn the ignition ON. Observe the Freeze Frame/Failure Records parameter with a scan tool and record the displayed data for this DTC. Start and operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions observed from the Freeze Frame/Failure Records. Observe the Long Term FT parameter. Does the scan tool indicate that the Long Term fuel trim is less than the specified value?	-21%	Go to Step 4	Go to Diagnostic Aids
4	Slowly operate the engine from idle to 3,000 RPM while observing the HO2S 1 and HO2S 2 parameters with a scan tool. Does the scan tool indicate that the heated oxygen sensor (HO2S) voltages are 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 air flow (MAF) sensor for blockage-Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . The 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 Resonator and Outlet 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 9	Go to Step 8
6	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 9	Go to Step 7
7	Test the HO2S high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	-	Go to Step 9	Go to Fuel System Diagnosis
8	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/CH47976) or Fuel Injector Diagnosis (w/J39021 or w/Tech 2) . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) . Did you find and correct the condition?	-	Go to Step 9	Go to Symptoms - Engine Mechanical
9	IMPORTANT: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim. Turn ON the ignition, with the engine OFF. IMPORTANT: DO NOT clear the codes with the engine running. The codes may reset in the same ignition cycle. 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 10
10	To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420. Refer to DTC P0420 . Did you complete the procedure?	-	Go to Step 11	Go to DTC P0420
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