DTC P0171 Fuel Trim System Lean. Oldsmobile Intrigue 1999

For 1990-2009 cars only

Makes 🢒 Oldsmobile 🢒 1999 🢒 Intrigue 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P0171 Fuel Trim System Lean

Circuit Description

To provide the best possible combination of driveability, fuel economy, and emission control, a closed loop air/fuel metering system is used. While in closed loop, the powertrain control module (PCM) monitors the HO2S 1 signal and adjusts fuel delivery based upon the HO2S signal voltage. A change made to fuel delivery is indicated by the long and short term fuel trim values which may be monitored with a scan tool. Ideal fuel trim values are around 0%. if the HO2S signals are indicating a lean condition the PCM adds fuel, resulting in fuel trim values above 0%. If a rich condition is detected, the fuel trim values are below 0%, indicating that the PCM is reducing the amount of fuel delivered. If an excessively lean condition is detected, the PCM sets DTC P0171.

The PCM's maximum authority to control long term fuel trim allows a range between -23% and +16%. The PCM's maximum authority to control short term fuel trim allows a range between -11% and +20%. The PCM monitors fuel trim under various operating conditions (fuel trim cells) before determining the status of the fuel trim diagnostic. The fuel trim cells are weighted (assigned a relative importance) as follows:

•	Idle, purge commanded (Cell 10 - approximately 10%).

•	Deceleration, purge commanded (Cell 1 - approximately 15%).

•	Normal driving, purge commanded (Cell 2 - approximately 25%).

•	Normal driving, no purge commanded (Cell 6 - approximately 45%).

•	Idle, no purge commanded (Cell 9 - approximately 5%).

The vehicle may have to be operated in all of the above conditions before the PCM determines fuel trim status. The amount that fuel trim deviates from 0% in each cell and the amount that each cell is weighted directly affects whether or not the vehicle must be operated in all of the cells described above to complete the diagnostic.

Conditions for Running the DTC

•	None of the following DTCs are present:

•	Throttle position (TP) sensor DTCs

•	Evaporative emissions (EVAP) DTCs

•	Intake air temperature (IAT) sensor DTCs

•	Manifold absolute pressure (MAP) sensor DTCs

•	Exhaust gas recirculation (EGR) pintle position DTCs

•	Engine coolant temperature (ECT) sensor DTCs

•	Crankshaft position (CKP) sensor DTCs

•	Camshaft position (CMP) sensor DTCs

•	Vehicle speed sensor (VSS) DTCs

•	Heated oxygen sensor (HO2S) DTCs

•	Mass air flow (MAF) sensor DTCs

•	Misfire DTCs

•	IC/Bypass DTCs

•	Fuel trim DTCs

•	Fuel injector circuit DTCs

•	The closed loop commanded air/fuel ratio is between 14.5 and 14.8

•	The ECT is between 20°C (68°F) and 110°C (230°F).

•	The IAT is between -18°C (0°F) and 70°C (158°F).

•	The BARO is more than 70 kPa.

•	The MAP is between 15 kPa and 85 kPa.

•	The throttle angle is less than 95%.

•	The vehicle speed is less than 82 mph.

•	The MAF is between 3 g/s and 150 g/s.

•	The engine speed is between 600 and 4000 RPM.

Conditions for Setting the DTC

•	Long term fuel trim is at or near maximum authority of +16%.

•	Short term fuel trim is at or near maximum authority of +20%.

•	All of the conditions are met in Fuel Trim Cells 1, 2, 5, 6, 9 and/or 10.

Action Taken When the DTC Sets

•	The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has run and failed.

•	The PCM stores the conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC

•	The PCM turns the MIL off during the third consecutive trip in which the diagnostic has run and passed.

•	The history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.

•	The DTC may be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids

Inspect for the following conditions:

•	Inspect the heated oxygen sensor wiring. The sensor pigtail may be routed incorrectly and contacting the exhaust system.

•	Verify that the PCM to engine block grounds are clean, tight, and in the proper locations. Refer to Ground Distribution Schematics in Electrical Diagnosis.

•	Test the fuel pressure. The system goes lean if the pressure is too low. The PCM may compensate for some decrease. However, if fuel pressure is too low, a DTC P0171 may be set.

Refer to Fuel System Pressure Test .

•	Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F) .

•	Inspect for any vacuum leaks. Inspect for the following conditions:

-	Any disconnected or damaged vacuum hoses.

-	An incorrectly installed or malfunctioning crankcase ventilation valve.

-	Any vacuum leaks at the throttle body, the EGR valve, and the intake manifold mounting surfaces.

•	Inspect for exhaust leaks. An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing the system to appear lean. Inspect for exhaust leaks that may cause a false lean condition to be indicated. Refer to Exhaust System Inspection .

•	Disconnect the MAF sensor and note if the lean condition is corrected. If the lean condition is corrected by disconnecting the sensor, replace the MAF sensor. Refer to Mass Airflow Sensor Replacement .

•	Test for fuel contamination. Water, even in small amounts, may be delivered to the fuel injectors. The water may cause a lean exhaust to be indicated. Excessive alcohol in the fuel may also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

•	Inspect for a faulty connection at the PCM. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connections.

•	Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 1 display on the scan tool while moving connectors and wiring harnesses related to the engine harness. A change in the display indicates the location of the malfunction.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description

The number(s) below refer to the step number(s) on the Diagnostic Table.

DTCs other than P0171 may indicate that a condition is present which may cause a lean condition. If this is the case, repairing the condition which caused the other DTC will most likely correct the DTC P0171.

If the DTC P0171 test passes while the Fail Records conditions are being duplicated, the lean condition is intermittent. Refer to Diagnostic Aids for additional information on diagnosing intermittent conditions.

DTC P0171 - Fuel Trim System Lean

Step	Action	Value(s)	Yes	No
1	Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Are any DTCs set other than P0171?	--	Go To Applicable DTCs	Go to Step 3
3	Start and run the vehicle in closed loop. Use a scan tool in order to observe the L.T. Fuel Trim and S.T. Fuel Trim. Are the displayed values more than the specified value?	+15%	Go to Step 5	Go to Step 4
4	Review and record the scan tool Fail Records data. Clear the DTC P0171 and operate the vehicle to duplicate the Fail Records conditions. Monitor the scan tool Specific DTC info for DTC P0171 while operating the vehicle to duplicate the Fail Records conditions. Continue operating the vehicle until the DTC P0171 test runs and note test result Does the scan tool indicate DTC P0171 Failed This Ign?	--	Go to Step 5	Go to Diagnostic Aids
5	Visually and physically inspect the vacuum hoses for splits, kinks, and improper connections. Refer to Emission Hose Routing Diagram . If a problem is found, repair as necessary. Was a problem found?	--	Go to Step 23	Go to Step 6
6	Visually and physically inspect the crankcase ventilation (PCV) valve for proper installation. Refer to Crankcase Ventilation System Inspection . If a problem is found, repair as necessary. Was a problem found?	--	Go to Step 23	Go to Step 7
7	Inspect the throttle body inlet screen for damage or for the presence of foreign objects which may alter the airflow sample through the mass air flow (MAF) sensor. If a problem is found, repair as necessary. Refer to Throttle Body Assembly Replacement . Was a problem found?	--	Go to Step 23	Go to Step 8
8	Start the engine and note the idle quality. Is a high or unsteady idle being experienced?	--	Go to Step 9	Go to Step 11
9	With the engine idling, observe the Idle Air Control display on the scan tool. Is the displayed value more than the specified value?	5 counts	Go to Step 11	Go to Step 10
10	Visually and physically inspect the throttle body, the intake manifold, the EGR valve, and the EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. Was a problem found?	--	Go to Step 23	Go to Step 11
11	Test the idle air control (IAC) system operation. Refer to the Idle Air Control (IAC) System Diagnosis . If a problem is found, repair as necessary. Was a problem found?	--	Go to Step 23	Go to Step 12
12	Test the fuel for excessive water, alcohol, or other contaminants. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . Was a problem found?	--	Go to Step 23	Go to Step 13
13	Visually and physically inspect the PCM injector grounds, power grounds and sensor grounds to ensure that they are clean, tight, and in their proper locations. If a problem is found, repair as necessary. Refer to Repair Procedures in Wiring Repairs in Wiring Systems.. Was a problem found?	--	Go to Step 23	Go to Step 14
14	Perform the Evaporative Emissions Control (EVAP) System Check. Refer to Evaporative Emission Control System Diagnosis . If a problem is found, repair as necessary. Was problem found?	--	Go to Step 23	Go to Step 15
15	Perform the Fuel System Pressure Test. Refer to Fuel System Pressure Test . If a problem is found, repair as necessary. Was problem found?	--	Go to Step 23	Go to Step 16
16	Visually and physically inspect the intake manifold, injector O-rings, EGR adapter, EGR valve and the EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. Was a problem found?	--	Go to Step 23	Go to Step 17
17	Visually and physically inspect the exhaust manifold for leaks and loose or missing hardware. If a problem is found, repair as necessary. Was a problem found?	--	Go to Step 23	Go to Step 18
18	Disconnect the MAF sensor electrical connector. Operate the vehicle in closed loop while monitoring the S.T Fuel Trim displayed on the scan tool. Does S.T Fuel Trim decrease to near the specified value?	0%	Go to Step 21	Go to Step 19
19	Check the fuel injector operation. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F) . If a problem is found, repair as necessary. Was a problem found?	--	Go to Step 23	Go to Step 20
20	Visually and physically inspect the HO2S to ensure that the sensor is installed securely and that the HO2S pigtail and wiring harness are not contacting the exhaust or otherwise damaged. If a problem is found, repair as necessary. Refer to Repair Procedures in Heated Oxygen Sensor Wiring Repairs . Was a problem found?	--	Go to Step 23	Go to Diagnostic Aids
21	Inspect the MAF sensor screen for foreign objects, debris, or damage. Is the MAF sensor screen OK?	--	Go to Step 22	Go to Step 23
22	Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the repair?	--	Go to Step 23	--
23	Review and record the scan tool Fail Records data. Clear the DTC P0171. Operate the vehicle to duplicate the Fail Records conditions. Monitor the scan tool Specific DTC info for DTC P0171 while operating the vehicle to duplicate the Fail Records conditions. Continue operating the vehicle until the DTC P0171 test runs and note test result. Does the scan tool indicate DTC P0171 Failed This Ign?	--	Go to Step 2	System OK