GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Optra 🢒 Engine 🢒 Engine Controls - 1.4L DOHC 🢒 DTC P0172

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, the ECM sets DTC P0172.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0172 Fuel Trim System Rich

Conditions for Running the DTC
    • DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0336, P0337, P0341, P0342, P0402, P0404, P0405, P0406, P0506, P0507, P1167, P1171, and P1404 are not set.
    • The engine coolant temperature (ECT) is between 70°C (158°F) and 115°C (239°F).
    • The barometric pressure is more than 72 kPa.
    • The calculated air flow is between 1.5 g/s and 45 g/s.
    • The manifold absolute pressure (MAP) sensor is between 25 kPa and 90 kPa.
    • The intake air temperature (IAT) is between -40°C (-40°F) and 120°C (248°F).
    • The engine speed is between 700 RPM and 6,000 RPM.
    • The throttle position (TP) sensor angle is less than 80 percent.
    • The vehicle speed is less than 140 km/h (87 mph).
    • The fuel system is operating in Closed Loop.
    • The ignition 1 voltage is more than 11 volts.
    • DTC P0172 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The average long term fuel trim cell values are less than -30 percent for 10 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the third 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 4 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 Intermittent Conditions .
    • Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: 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 also set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  1. Start the engine.
  2. Allow the engine to reach the normal operating temperature and enter Closed Loop.
  3. Observe the Long Term FT parameter with a scan tool.

Is the Long Term FT less than the specified value?

-30 %

Go to Step 4

Go to Diagnostic Aids

4
  1. Start the engine.
  2. Put the transmission in Park or Neutral position.
  3. Turn OFF all of the accessories.
  4. Allow the engine to idle.
  5. 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 5

Go to DTC P0107

5

  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 6

Go to Step 7

6
  1. Turn OFF the engine.
  2. Inspect for the following conditions:
    3. • Splits, kinks, or improper connections at the vacuum hoses.
    • The air intake duct for being collapsed or restricted
    • The air filter for being dirty or restricted
    • For objects blocking the throttle body

Did you find and correct the condition?

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Go to Step 9

Go to Step 8

7
  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 9

Go to Fuel System Diagnosis

8

Inspect for the following conditions:

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

Did you find and correct the condition?

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Go to Step 9

Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC)

9
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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?

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Go to Step 2

Go to Step 10

10

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