GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Rainier 🢒 Engine 🢒 Engine Controls - 5.3L 🢒 DTC P0172 or P0175

Circuit 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. During Open Loop the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During Closed Loop, the oxygen sensor inputs are added and used by the ECM to calculate short and long term fuel trim fuel delivery adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicates a rich condition, the fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response to the HO2S voltage signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. The fuel trim 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 rich condition, DTC P0172 or P0175 sets.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

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

Conditions for Running the DTC
    • DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0156, P0157, P0158, P0160, P0161, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0300, P0442, P0443, P0446, P0449, P0455, P0496, P0506, P0507, P1133, P1134, P1153, or P1154 are not set.
    • The engine coolant temperature (ECT) is between -40 and +140°C (-40 and +284° F).
    • The intake air temperature (IAT) is between -20 and +152°C (-4 and +304°F).
    • The manifold absolute pressure (MAP) is between 15-105 kPa (2.2-15.2 psi).
    • The vehicle speed is less than 132 km/h (82 mph).
    • The engine speed is between 400-6,500 RPM.
    • The barometric pressure (BARO) is more than 70 kPa (10.2 psi).
    • The mass air flow (MAF) is between 1-250 g/s.
    • The fuel level is more than 10 percent.
    • This diagnostic runs continuously when the above conditions are met.

Conditions for Setting the DTC
    • The average long term fuel trim value is below 17 percent.
    • The above condition is present for 40 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
    • Fuel contamination, such as water or alcohol will effect fuel trim.
    • A malfunctioning (MAF) sensor can cause a rich condition and set this DTC. Refer to DTC P0101 .
    • Review Failure Records with a scan tool.
    • If an intermittent condition is suspected , refer to Intermittent Conditions .

Test Description

The number below refers to the step number on the diagnostic table.

  1. An evaporative emission (EVAP) canister that is saturated will cause a rich condition.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Are any DTCs other than DTC P0172 or P0175 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 3

3
  1. Install scan tool.
  2. Start and idle the engine at the normal operating temperature in Closed Loop.
  3. Record the long term fuel trim data.
  4. Turn OFF the engine.
  5. Turn ON ignition, with the engine OFF.
  6. Review the Freeze Frame/Failure Records and record the displayed data for this DTC.

Does the scan tool indicate that the long term fuel trim is less than the specified value?

-17%

Go to Step 4

Go to Diagnostic Aids

4
  1. Operate engine at idle.
  2. Observe HO2S parameters with a scan tool.

Does the scan tool indicate that the values are within the specified range and fluctuating?

200-800 mV

Go to Step 5

Go to Step 6

5
  1. Turn OFF the engine.
  2. Visually and physically inspect the following items:
    3. • The evaporative emission (EVAP) lines and components for damage or blockage--Refer to Evaporative Emissions Hose Routing Diagram .
    • The inlet screen of the mass air flow (MAF) sensor for blockage
    • The vacuum hoses for splits, kinks, and proper connections--Refer to Emission Hose Routing Diagram .
    • The air intake duct for being collapsed or restricted
    • The air filter for being dirty or restricted
    • Inspect for objects blocking the throttle body.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

6

  1. Turn OFF the engine.
  2. Inspect the heated oxygen sensor (HO2S) for proper installation.
  3. Inspect to ensure that the electrical connectors and the wires are secure and not contacting the exhaust system.
  4. Test for continuity between the signal circuit and the low reference circuit. Refer to the following in Wiring Systems:

Did you find and correct the condition?

--

Go to Step 8

Go to Fuel System Diagnosis

7

Inspect for the following:

    • Excessive fuel in the crankcase
    • Proper operation of the fuel pressure regulator--Refer to Fuel System Diagnosis .
    • All injectors are functioning properly--Refer to Fuel Injector Solenoid Coil Test .

Did you find and correct the condition?

--

Go to Step 8

Go to Symptoms - Engine Mechanical in Engine Mechanical

8

Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.

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

9

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK