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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 SLS 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 DTC P0171, P0172, P0174, or P0175

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    •  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0171: Fuel Trim System Lean Bank 1

DTC P0172: Fuel Trim System Lean Bank 1

DTC P0174: Fuel Trim System Lean Bank 2

DTC P0175: Fuel Trim System Rich Bank 2

Circuit/System Description

The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicate a lean condition, fuel trim values will be above 0 percent, if the HO2S indicate a lean condition, fuel trim values will be above 0 percent, the short term FT values change rapidly in response to the HO2S signal voltage. The long term FT makes coarse adjustments in order to maintain an optimum air/fuel ratio. A memory block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and engine load. The FT diagnostic will conduct a test to determine if a rich failure actually exists, or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition.

If the ECM detects an excessively lean condition, DTC P0171 or P0174 is set. If the ECM detects an excessively rich condition, DTC P0172 or P0175 is set.

Conditions for Running the DTC

P0171, P0174

    • DTCs P0050, P0056, P0059, P0060, P0068, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0120, P0122, P0123, P0128, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0201, P0208, P0220, P0222, P0223, P0300, P0301, P0308, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P0506, P0507, P1153, P1516, P2101, P2119, P2120, P2125, P2135, P2138, P2A03, P2A04 are not set.
    • The engine speed is between 400-6,000 RPM.
    • The barometric pressure (BARO) is more than 70 kPa (10.1 psi).
    • The engine coolant temperature (ECT) is at -38 to +150°C (-36.4 to +302°F).
    • The manifold absolute pressure (MAP) is between 5-255 kPa (0.7-36.9 psi).
    • The engine coolant temperature (ECT) is at -38 to +150°C (-36.4 to +302°F).
    • The mass air flow (MAF) is between 0.5-510 g/ s.
    • The vehicle speed is less than 134 km/h (83 mph).
    • The engine is in CL status.
    • Fuel Trim Learn is enabled.
    • Not in Status of Output Control.
    • The EGR valve intrusive diagnostic tests is inactive.
    • The three-way catalytic monitor intrusive diagnostic tests is inactive.
    • The post oxygen sensor intrusive diagnostic tests is inactive.
    • The evaporative emission canister diagnosis is not in the lower of the canister test part.
    • DTC P0171 or P0174 runs continuously when the above conditions are met.

P0172, P0175

    • DTCs P0050, P0056, P0059, P0060, P0068, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0120, 0122, P0123, P0128, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0201, P0208, P0220, P0222, P0223, P0300, P0301, P0308, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P0506, P0507, P1153, P1516, P2101, P2119, P2120, P2125, P2135, P2138, P2A03, P2A04 are not set.
    • The engine speed is between 400-6,000 RPM.
    • The barometric pressure (BARO) is more than 70 kPa (10.1 psi).
    • The engine coolant temperature (ECT) is at -38 to +150°C (-36.4 to +302°F).
    • The manifold absolute pressure (MAP) is between 5-255 kPa (0.7-36.9 psi).
    • The engine intake air temperature (IAT) is at -38 to +150°C (-36.4 to +302°F).
    • The mass air flow (MAF) is between 2.89-510 g/ s.
    • The vehicle speed is less than 134 km/h (83 mph).
    • The engine is in CL status.
    • Fuel Trim Learn is enabled.
    • Not in Status of Output Control.
    • The EGR valve intrusive diagnostic tests is inactive.
    • The three-way catalytic monitor intrusive diagnostic tests is inactive.
    • The post oxygen sensor intrusive diagnostic tests is inactive.
    • The evaporative emission canister diagnosis is not in the lower of the canister test part.

Intrusive Test

    • Lack Non-Purge data prior to Purge data.
    • The long purge term FT weighted average value is less than a calibrated value.
    • The engine speed is more than 400 RPM.
    • The mass air flow (MAF) is between 2.89-510 g/ s.
    • The manifold absolute pressure (MAP) is between 5-255 kPa (0.7-36.9 psi).
    • DTC P0172 or P0175 runs continuously when the above conditions are met.

Conditions for Setting the DTC

P0171, P0174

    • The long term FT weight average value is more 100 ms than the specified value.
    • DTCs P0171, P0174 is set when the above conditions are met.

P0172, P0175

    • When performing the passive test, the long non-purge term FT weight average value is less 100 ms than the standard value.
    • When performing the intrusive tests, once the fuel test passes over 3 times, the number of a rich condition exceeds 3 times, the diagnosis fails.
    • DTC P0172, P0175 is set when the above conditions are met.

Action Taken When the DTC Sets
    • DTC P0171 P0172, P0174 and P0175 are Type B DTCs.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second ignition cycle, the control module records the operating conditions at the time the diagnosis fails. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. The control module illuminates the malfunction indicator lamp (MIL) when one of the following occurs:
       - The control module detects the same fuel trim failure during 2 consecutive ignition cycle trips.
       - The control module detects any fuel trim failure during any subsequent trip if the conditions at the time of failure meet the followings:
   • The engine load is within 20 percent of the previous test that failed.
   • The engine speed is within 375 RPM of the previous test that failed.
   • The engine coolant temperature is in the same range of the previous test that failed.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) at the beginning of the fourth ignition cycle, after 3 continuous ignition cycles that the diagnosis runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC and related Freeze Frame data clears after 40 warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Reference Information

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Emission System Information Reference

    •  Evaporative Emissions Hose Routing Diagram
    •  Crankcase Ventilation System Inspection/Diagnosis

Engine Mechanical Information Reference

    •  Symptoms - Engine Mechanical
    •  Symptoms - Engine Exhaust

Fuel System Information Reference

    •  Fuel System Diagnosis
    •  Alcohol/Contaminants-in-Fuel Diagnosis

DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Engine Control Module Scan Tool Information

Circuit/System Verification

Important: Disregard automatic 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.

    • Verify that no other DTCs are set.
       ⇒If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
    • Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.
       ⇒If the value does not vary from approximately 40 mV to approximately 900 mV, refer to the following:
      •  DTC P0131, P0132, P0137, or P0138
      •  DTC P0133, P0134, P0140, P1133, or P2A00
      •  DTC P0151, P0152, P0157, or P0158
      •  DTC P0153,P0154, P0160, P1153, or P2A03

       Important: EVAP purge enablement may cause the FT to be momentarily outside the normal range.

    • The normal short term FT parameter should be between +10 and -10 percent, with near 0 percent the optimum, the engine running at operating temperature.
    • The long term FT parameter should be between +10 and -10 percent, with near 0 percent the optimum, the engine running at operating temperature.

Circuit/System Testing

P0171 or P0174

Allow the engine to reach operating temperature. With the engine running, observe the affected long term FT parameter with a scan tool. The value should be less than approximately 24 percent with the engine running at the operating temperature.

⇒If the value is more than 24 percent, inspect for the following:
    • With the engine OFF, turn the ignition ON, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .
       ⇒If the MAP sensor does not indicate the correct barometric pressure, refer to DTC P0106 and DTC P0107 or P0108 .
    • Vacuum hoses for splits, kinks, and improper connections
    • Insufficient fuel in the tank
    • A MAF condition--Refer to DTC P0068 or P0121 or DTC P0101 or P1101 .
    • Low fuel pressure
    • Fuel contamination
    • Injector fault
    • Missing, loose, or leaking exhaust components from the HO2S forward
    • Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
    • The induction system and intake air duct for leaks or for a missing air filter element
    • A cracked or damaged EVAP canister
    • Evaporative canister purge lines plugged or obstructed
    • The crankcase ventilation system for leaks
    • The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system
    • The HO2S signal circuit open, short to ground, or short to the low reference circuit
    • The HO2S sensor 1 low signal circuit for an open circuit or high resistance
    • Malfunctioning engine components

P0172 or P0175

Allow the engine to reach operating temperature. With the engine running, observe the affected long term FT parameter with a scan tool. The value should be more than approximately -23 percent with the engine running at operating temperature.

⇒If the value is less than -23 percent, inspect for the following:
    • With the engine idling and the transmission in the Park or Neutral position, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor parameter should be between 19-42 kPa.
       ⇒If the MAP sensor parameter is not within 19-42 kPa, refer to DTC P0106 and DTC P0107 or P0108 .
    • Vacuum hoses for splits, kinks, and improper connections
    • The inlet screen of the mass air flow sensor for blockage
    • A MAF condition--Refer to DTC P0068 or P0121 or DTC P0101 or P1101 .
    • The air duct for being collapsed or restricted
    • The air filter for being dirty or restricted
    • Objects blocking the throttle body
    • Excessive fuel in the crankcase
    • The evaporative emissions control system for improper operation
    • Excessive fuel pressure
    • Improperly functioning injectors
    • Fuel contamination
    • The HO2S for proper installation and for electrical wires and connectors that may have contacted the exhaust system
    • The HO2S signal circuit shorted to voltage

Repair Instructions
    •  Air Cleaner Assembly Replacement
    •  Air Cleaner Element Replacement
    •  Evaporative Emission Canister Replacement
    •  Evaporative Emission Canister Purge Solenoid Valve Replacement
    •  Evaporative Emission Hoses/Pipes Replacement - Chassis/Canister
    •  Fuel Injector and Fuel Rail Replacement
    •  Primary Fuel Level Sensor Replacement
    •  Fuel System Cleaning
    •  Fuel Tank Draining
    •  Heated Oxygen Sensor Replacement - Bank 1 Sensor 1
    •  Heated Oxygen Sensor Replacement - Bank 1 Sensor 2
    •  Manifold Absolute Pressure Sensor Replacement
    •  Throttle Body Assembly Replacement

Repair Verification

Important: 

   • After repairing, reset the long term fuel with the scan tool Fuel Trim Reset function.
   • In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle under the conditions of running and setting DTC P0420, P0430 and verify that DTC P0420 or P0430 runs and passes.

  1. The installed or replaced components or connector during diagnosis.
  2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
  3. Turn the ignition to ON without the engine running.

    4. Important: DO NOT clear codes with the engine running. DTC may be reset in the same ignition cycle.

  4. Clear the DTC.
  5. Turn the ignition OFF for 60 seconds.
  6. Start the engine.
  7. Duplicate the Conditions for Running the DTC and use Freeze Frame/Failure Records, if applicable, in order to verify that the DTC does not reset. If the DTC resets or another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedures.