Safety Warning

DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.

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HOMESERVICE MANUALSBUICK2006TERRAZA CXL, 3.5 L, AWDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 147 (ENGINE CONTROL SYSTEM - 3.8L - DTC P0016 TO DTC P0206)DTC P0171TEST DESCRIPTION

2006 Buick Terraza CXL, 3.5 L, AWD

Test Description

2006 Buick Terraza CXL, 3.5 L, AWDSECTION Test Description

WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

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

10: If conditions were not corrected, a worn CAM, worn intake or exhaust valves or other 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	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 HO2S 1 parameter 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: Vacuum hoses for splits, kinks and proper connections-Refer to Emission Hose Routing Diagram (L26, NU3) . 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 (With 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 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 vs 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 (MAP) Sensor Diagnosis
7	Turn OFF the engine. Inspect the HO2S for proper installation. Refer to Heated Oxygen Sensor Replacement - Position 1 . 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 for 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 intake ducts for leaks or for a missing air filter element-Refer to Air Cleaner Assembly Replacement and Air Cleaner Intake Duct Replacement . Evaporative canister purge lines plugged or obstructed Properly functioning fuel injectors-Refer to Fuel Injector Coil Test . 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	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

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.
• Brakes feel soft, pull hard to one side, or make grinding noises.
• The engine overheats, stalls repeatedly, or misfires under load.
• You are missing required tools, torque specs, or safe lifting equipment.
• You are not confident in the next step or safety outcome.