GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Epica 🢒 Engine 🢒 Engine Controls - 2.5L (LBK) 🢒 DTC P0172 or P0175

Circuit Description

The engine control module (ECM) controls a Closed Loop air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage and adjusts the fuel delivery based on the signal voltage while in Closed Loop. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltages. These changes fine tune the engine fueling. The long term fuel trim values change in response to trends in the short term fuel trim. The long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the ECM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition. The fuel trim cells are based on the engine speed and load. If the ECM detects an excessively rich condition, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTCs:

    • DTC P0172 Fuel Trim System Rich Bank 1
    • DTC P0175 Fuel Trim System Lean Bank 2

Conditions for Running the DTC
    • DTCs P0030, P0031, P0032, P0050, P0051, P0052, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0151, P0152, P0153, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0276, P0277, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0400, P0401, P0402, P0403, P0404, P0405, P0406, P0444, P0445, P0501, P1504, are not set.
    • The engine is operating.
    • The engine coolant temperature (ECT) is more 20°C (68°F).
    • The barometric pressure (BARO) is more than 74.5 kPa.
    • The fuel system is in closed loop.
    • The EVAP canister has been purge for 240 seconds, then it is disabled for 60 seconds.
    • The DTCs run continuously once the above conditions are met.

Conditions for Setting the DTC

The accumulated value of Long Term and Short Term fuel trim cells are less than -32 percent for 60 seconds.

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 system will become rich if a fuel injector is supplying too much fuel.
    • Test for fuel contamination. Water or alcohol can effect fuel trim. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Intermittent Conditions .

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Are any DTCs other than P0172 or P0175 also set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  1. Start the engine.
  2. Observe the TP Sensor parameter with a scan tool.

Is the TP Sensor within the specified range?

2-10 %

Go to Step 4

Go to DTC P0123

4
  1. Start the engine.
  2. Allow the engine to reach the normal operating temperature and enter Closed Loop.
  3. Observe the Long Term FT and Short Term FT parameters with a scan tool.
  4. Add the percentages of the Long Term FT and Short Term FT together.

Is the percentage less than the specified value?

-32 %

Go to Step 5

Go to Diagnostic Aids

5

  1. Put the transmission in Park or Neutral position.
  2. Turn OFF all of the accessories.
  3. Allow the engine to idle.
  4. Observe the manifold absolute pressure (MAP) sensor parameter with a scan tool.

Is the MAP sensor parameter within the specified range?

19-50 kPa

Go to Step 6

Go to DTC P0106

6
  1. Operate the engine at idle.
  2. Observe the heated oxygen sensor (HO2S) 1 parameter with a scan tool.

Is the voltage within the specified range and fluctuating?

200-800 mV

Go to Step 7

Go to Step 8

7
  1. Turn OFF the engine.
  2. Inspect for the following conditions:
    3. • Splits, kinks, or improper connections at the vacuum hoses. Refer to Emission Hose Routing Diagram .
    • The air intake duct for being collapsed or restricted
    • The air filter for being dirty or restricted
    • For objects blocking the throttle body
    • Leaking vacuum fuel pressure regulator--allowing fuel into the vacuum line.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 9

8

  1. Turn OFF the engine.
  2. Inspect for the following conditions:
    3. • The correct installation of the HO2S 1
    • That the HO2S 1 electrical connectors and wires are secured and not contacting the exhaust system.
    • The HO2S signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Fuel System Diagnosis

9

Inspect for the following conditions:

    • Excessive fuel in the crankcase
    • The evaporative emissions control system for proper operation
    • The fuel system for the correct operation. Refer to Fuel System Diagnosis .
    • Ensure that all injectors are functioning correctly. Refer to Fuel Injector Balance Test with Special Tool .
    • Fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?

--

Go to Step 10

Go to Symptoms - Engine Mechanical in Engine Mechanical - 2.5L (LBK)

10
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Reset the fuel trim values with a scan tool.
  5. Operate the vehicle within the Conditions for Running 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 11

11

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK