DTC P0171 Fuel Trim System Lean Bank 1. Chevrolet Caprice 1996

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 Caprice 🢒 DTC 🢒 DTC P0171 Fuel Trim System Lean Bank 1

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 PCM monitors the heated oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery will be indicated by the Long and Short Term Fuel Trim values. Short Term Fuel Trim values change rapidly in response to the HO2S signal voltages. These changes fine tune engine fueling. Long Term Fuel Trim values change in response to trends in Short Term Fuel Trim. Long Term Fuel Trim makes coarse adjustments to fueling in order to re-center and restore control to Short Term Fuel Trim. Short and Long Term Fuel Trim can be monitored with a scan tool. Ideal fuel trim values are around 0%. A positive Fuel Trim value indicates that the PCM is adding fuel to compensate for a lean condition. A negative Fuel Trim value indicates that the PCM is reducing the amount of fuel to compensate for a rich condition. If an excessively Rich or Lean condition is detected, the PCM will set a DTC. The long term fuel trim diagnostic parameter is an average of several of the long term speed load learn cells which are selected based on speed and load.

Conditions for Setting the DTC

•	DTCs P0100, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0200, P0300, P0372, P0441, P0443, P0500, P0601, P1133, P1153, P1351, P1361, P1371, P1415, P1416, P1441 not set.

•	Engine Coolant Temperature between 60°C (120°F) and 115°C (239°F).

•	Fuel system operating in Closed Loop.

•	Fuel trim enabled.

•	Barometric Pressure greater than 70 kPa.

•	Mass Air Flow between 5 grams per second and 100 grams per second.

•	Manifold Absolute Pressure between 20 kPa and 90 kPa.

•	Intake Air Temperature between -30°C (-22°F) and 150°C (302°F).

•	EVAP Canister purge not enabled or EVAP Canister purge duty cycle greater than 75%.

•	Engine speed between 500 RPM and 4000 RPM.

•	TP Sensor angle less than 75%.

•	Vehicle speed less than 121 km/h (75 mph).

•	The PCM detects the average Long Term Fuel Trim cell values are above a predetermined threshold.

•	All above conditions met for approximately 10 seconds.

Action Taken When the DTC Sets

•	The PCM will illuminate the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails, if the diagnostic fails under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed.

•	The first time the diagnostic fails, the PCM will record operating conditions in Failure Records.

•

The second consecutive drive trip that this diagnostic fails [under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed], this information will be stored in Freeze Frame. Any data previously stored in Freeze Frame will be copied into Failure Records and Freeze Frame will be overwritten by this DTC. The only exception to this is if a Misfire DTC was already recorded in Freeze Frame. In this case, the Misfire data stays in Freeze Frame and the Fuel Trim data will be updated in Failure Records.

Conditions for Clearing the MIL/DTC

•	The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail within the same conditions that the DTC last failed.

Important: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than three drive trips. Review Freeze Frame/Failure Records for the last failure conditions.

•	A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.

•	PCM battery voltage is interrupted.

•	Using a Scan tool.

Diagnostic Aids

•	If a DTC P0171 cannot be duplicated, it may have been caused by the customer running the vehicle out of fuel.

•	A fuel delivery malfunction will cause this DTC to set. Thoroughly inspect all items that can cause a lean condition.

•	For intermittents, refer to Symptoms

Test Description

Number(s) below refer to step numbers on the diagnostic table.

Determines whether the fault is present. For any test that requires probing the PCM or a component harness connector, must use the Connector Test Adapter Kit J 35616-A. Using this kit will prevent damage to the harness connector terminals.

Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed.

If DTC 174 is also set indicates both banks of the engine are operating lean. Inspect items that would cause both banks to operate lean.

A vacuum leak will cause DTCs P0171 and P0174 to set at the same time. Inspect all areas of the engine for a vacuum leak. Also inspect PCV valve for being the correct one for this application. Make sure the engine oil fill cap is in place and that its tight. Check that the engine oil dip stick is fully seated.

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Important: If any DTCs are set (Except P0171 and P0174) refer to those DTCs before proceeding with this diagnostic.

Install the scan tool.
Start and idle the engine until normal operating temperature is reached.
Fuel system in Closed Loop.
Using a scan tool, monitor LT FT Bn 1 and ST FT Bn 1 display on the Fuel Trim Data List.

Is the LT FT and the ST FT less than the specified values indicated?

22% LT

10% ST

Go to Step 3

Go to Step 4

Turn the ignition ON, engine OFF, review Freeze Frame and/or Failure Records data for this DTC and note parameters.
Turn the ignition OFF for 15 seconds.
Start the engine and operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in Freeze Frame/Failure Records as possible. Special operating conditions that need to be met before the PCM will run this diagnostic, where applicable, are listed in Conditions for Setting the DTC.
Using the scan tool, select DTC, Specific, then enter the DTC number which was set.

Does the scan tool indicate that this diagnostic failed this ignition?

Go to Step 4

Refer to Diagnostic Aids

Is DTC P0174 also set?

Go to Step 5

Go to Step 6

Visually/physically inspect the following items:

•	Vacuum hoses for splits, kinks and proper connections. Refer toUnder Hood Vacuum Hose Routing Diagrams.

•	Throttle body, intake manifold and EGR valve for vacuum leaks.

•	Crankcase ventilation valve and/or system for leaks.

•	Contaminated fuel. Refer to Crankcase Ventilation System .

•	PCM and sensor grounds are clean tight and in proper locations.

•	Air induction system after MAF sensor for vacuum leaks.

•	Engine mechanical failure. Refer to Engine General Information.

Was a problem found in any of the above areas?

Go to Step 7

Go to Fuel System Diagnosis

Visually/physically inspect the following items:

•	Bank 1 exhaust leaks, missing or loose exhaust hardware.

•	Bank 1 HO2S 1 is installed securely and electrical connector not contacting exhaust system or ignition wires.

•	Engine mechanical failure. Refer toEngine General Information.

•	Vacuum leaks that will only affect bank 1 (Intake manifold, injector "O" rings, etc.)

Was a problem found in any of the above areas?

Go to Step 7

Go to Fuel System Diagnosis

Repair or replace any faulty items found.

Is the action complete?

Go to Step 8

Using the scan tool, select DTC, Clear Info.
Start the engine and idle at normal operating temperature.
Select DTC, Specific, then enter the DTC number which was set.
Operate the vehicle within the conditions for setting this DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?

Go to Step 9

Go to Step 2

Using the scan tool, select Capture Info, Review Info.

Are any DTCs displayed that have not been diagnosed?

Go to the applicable DTC table

System OK