GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2006 🢒 G6 🢒 Engine 🢒 Engine Controls - 3.9L 🢒 DTC P1174 or P1175

DTC Descriptors

DTC P1174: Air Fuel Imbalance Bank 1

DTC P1175: Air Fuel Imbalance Bank 2

Diagnostic Fault Information

Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit/System Description

The air fuel imbalance monitor (AFIM) diagnostic detects a rich or lean cylinder to cylinder air/fuel ratio imbalance in each bank. The diagnostic monitors the pre-catalyst heated oxygen sensor (HO2S) signal's frequency and amplitude characteristics by calculating an accumulated voltage over a predetermined sample period. An imbalance is indicated when multiple samples of the accumulated voltage are consistently higher than the desired value.

Conditions for Running the DTC
    • DTCs P0030, P0036, P0050, P0053, P0059, P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0128, P0131, P0132, P0133, P0134, P0135, P0151, P0152, P0153, P0154, P0155, P0201-P0206, P0300, P0301-P0306, P0411, P0412, P0418, P0442, P0443, P0446, P0449, P0452, P0453, P0454, P0455, P0496, P1133, P1153, P1516, P2101, P2119, P2120, P2125, P2135, P2138, P2176, P2431, P2432, P2433, P2440, P2A00, P2A03 are not set.
    • The device control is not active.
    • The intrusive diagnostics are not active.
    • The engine overspeed protection is not active.
    • The power take-off (PTO) is not active.
    • The traction control is not active.
    • The fuel control is in air-fuel Closed Loop.
    • The system voltage is greater than 10 volts, or less than 18 volts.
    • The engine run time is greater than 50 seconds.
    • The engine coolant temperature (ECT) is greater than 10°C (50°F).
    • The engine speed is greater than 1,000 RPM, but less than 4,000 RPM.
    • The mass air flow is greater than 7 g/s, but less than 400 g/s.

Conditions for Setting the DTC

Multiple samples of the pre-catalyst HO2S accumulated voltage are consistently higher than the desired value.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • 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 consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive 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.

Diagnostic Aids
    • The fuel trim cylinder balance diagnostic is very sensitive to heated oxygen sensor (HO2S) design. A non-OE sensor or an incorrect part number may set a false DTC.
    • Monitoring the misfire current counters, or misfire graph, may help to isolate the cylinder that is causing the condition.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Controls Connector End Views
    •  Engine Control Module Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Troubleshooting with a Test Lamp
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Output Controls

Special Tools Required

    • J 34730-1A Fuel Pressure Gage
    •  J 39021 Fuel Injector Coil and Balance Tester
    • J 39021-210 Injector Tester Adapter Box
    •  J-39021-450 Fuel Injector Harness Adapter

Circuit/System Testing
  1. Read and record the Freeze Frame/Failure Records data taking note of the speed and load at which the DTC set.
  2. Diagnose any other DTCs that are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  3. 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.
    4. ⇒If the MAP sensor parameter is not between 19-42 kPa, refer to DTC P0106, P0107, or P0108 .
  4. Inspect the air induction system for modified, damaged, leaking, or restricted components.
  5. Inspect the crankcase ventilation system for improper operation.
  6. Inspect the vacuum hoses for splits, kinks, and improper connections.
  7. Inspect for vacuum leaks at the intake manifold, the throttle body, and the injector O-rings.
  8. Test for a restricted, damaged, leaking, or modified exhaust system from the catalytic converter forward. Refer to Symptoms - Engine Exhaust .
  9. Test the fuel injectors for improper operation. Refer to Fuel Injector Diagnosis .
  10. Test for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
  11. Test for excessive fuel in the crankcase due to leaking injectors.
  12. Test the ignition system for improper operation. Refer to Electronic Ignition (EI) System Diagnosis .
  13. Test the engine for any mechanical conditions such as sticking valves, lifters, etc., which could alter the flow into the combustion chamber. Refer to Symptoms - Engine Mechanical .

Repair Instructions

Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verify the repair under the same speed and load as noted in the Freeze Frame/Failure Records data recorded during testing.