GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Classic 🢒 DTC 🢒 DTC P0172

Circuit Description

The powertrain control module (PCM) 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 Loop and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During Closed Loop, the PCM adds HO2S inputs and level of purge to calculate the short and long term fuel trim adjustments. If the HO2S indicate a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicate a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the HO2S voltage signals. The 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. This DTC is continuously monitored during engine operation. If the PCM detects an excessively rich condition, DTC P0172 sets.

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 , P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0141, P0201-P0204, P0300, P0301-P0304, P0326, P0336, P0340, P0341, P0442, P0446, P0452, P0453, P0455, P0481, P0496, P0502, P0503, P0506, P0601, P0602, P0604, P0606, P1133, P1621 are not set.
    • The engine is in Closed Loop status.
    • The engine coolant temperature (ECT) is between 60-115°C (140-239°F).
    • The intake air temperature (IAT) is between -25 to +115°C (-13 to +239°F).
    • The manifold absolute pressure (MAP) is more than 26 kPa (3.8 psi).
    • The vehicle speed is less than 132 km/h (82 mph).
    • The engine speed is between 550-3,600 RPM.
    • The barometric pressure (BARO) is more than 72 kPa (10.4 psi).
    • DTC P0172 runs continuously once the above conditions are met.

Conditions for Setting the DTC
    • The average long term fuel trim value is below -46 percent.
    • The above condition is present for 16 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 and alcohol will affect the fuel trim.
    • The system will go rich if the injectors are supplying too much fuel.
    • Use a scan tool in order to review the Failure Records. If an intermittent condition is suspected , refer to Intermittent Conditions .

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 P0172 also set?

--

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

Go to Step 3

3
  1. Install a scan tool.
  2. Review the Freeze Frame/Failure Records and record the displayed data for this DTC.
  3. Select Fuel and Emission data list.
  4. Start the engine.
  5. Observe the Long Term FT parameter with a scan tool.

Is the Long Term FT less than the specified value?

-46%

Go to Step 4

Go to Diagnostic Aids

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

Is the MAP sensor parameter within the specified range?

19-42 kPa

Go to Step 5

Go to DTC P0106

5
  1. Operate the engine at idle.
  2. Observe the heated oxygen sensor (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 6

Go to Step 7

6
  1. Turn OFF the engine.
  2. Visually and physically inspect the following items:
    3. • 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
    • For objects blocking the throttle body

Did you find and correct the condition?

--

Go to Step 9

Go to Step 8

7
  1. Turn OFF the engine.
  2. Inspect for the following conditions:
    3. • The HO2S for proper installation
    • Ensure that the 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:

    • 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 properly. Refer to Fuel Injector Solenoid Coil Test .
    • Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?

--

Go to Step 9

Go to Symptoms - Engine Mechanical in Engine Mechanical

9

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

  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?

--

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 - Vehicle in Vehicle DTC Information

System OK