For 1990-2009 cars

Table 1: | DTC P0172 - Fuel Trim System Rich

### Circuit Description

To provide the best possible combination of driveability, fuel economy, and emission control, a closed loop air/fuel metering system is used. While in closed loop, the power train control (PCM) monitors the HO2S 1 signal and adjusts fuel delivery based upon the HO2S signal voltages. A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim values are around 0 percent if the HO2S signals are indicating a lean condition the PCM will add fuel, resulting in fuel trim values above 0 percent. If a rich condition is detected, the fuel trim values will be below 0 percent, indicating that the PCM is reducing the amount of fuel delivered. If an excessively rich condition is detected, the PCM will set DTC P0172. The PCMs maximum authority to control long term fuel trim allows a range between -30 percent and +22 percent. The PCMs maximum authority to control short term fuel trim allows a range between -27 percent and +27 percent. The PCM monitors fuel trim under various operating conditions (fuel trim cells) before determining the status of the fuel trim diagnostic. The fuel trim cells are as follows:

Cell | Purge ON | Purge OFF
--- | --- | ---
Idle (Cell 0) | X | --
Decel (Cell 1) | X | --
Normal (Cell 2) | X | --
Accel (Cell 3) | -- | --
High Flow (Cell 4) | -- | --
L.T. Fuel Trim average less than -19%
S.T. Fuel Trim less than 1%

The vehicle may have to be operated in all of the above conditions marked by an X, before the PCM determines fuel trim status. The amount of fuel trim deviates from 0 percent in each cell and the amount that each cell is used directly affects whether or not the vehicle must be operated in all of the cells described above to complete the diagnostic.

### Conditions for Running the DTC

• | No MAF, ECT, TP, MAP, CMP, CKP, IAT sensor, EVAP, EGR, HO2S, Misfire, Injector circuit, Idle speed, VSS, or IC circuit DTCs set.

• | Engine coolant temperature between 20°C (68°F) and 110°C (230°F).

• | Intake air temperature is between -18°C (0°F) and 70°C (158°F).

• | Manifold absolute pressure is between 18 kPa and 80 kPa.

• | Throttle angle is steady and less than 90 percent.

• | Vehicle speed is less than 132 km/h (82 mph).

• | Engine speed is between 600 and 4000 RPM.

• | BARO is greater than 70 kPa.

• | Air flow is between 3 gm/s and 150 gm/s.

### Conditions for Setting the DTC

• | Long term fuel trim is at or near maximum authority of -19 percent.

• | Short term fuel trim is at or near maximum authority of 1 percent.

• | All conditions have been met in the fuel trim cells.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.

• | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using the scan tool.

### Diagnostic Aids

Inspect the following items:

• | Fuel pressure high -- The system will go rich if pressure is too high. The PCM can compensate for some increase. However, if fuel pressure is too high, a DTC P0172 may be set. Refer to Fuel System Pressure Test .

• | Fuel injectors faulty -- Refer to Fuel Injector Balance Test .

• | Inspect the EVAP canister for fuel saturation. If the EVAP canister is full of fuel, check canister control and hoses.

• | Disconnect the MAF sensor and see if rich condition is corrected. If so, replace the MAF sensor. Refer to Mass Airflow Sensor Replacement .

• | Inspect for a leaking fuel pressure regulator diaphragm by checking the vacuum line to the fuel pressure regulator for the presence of fuel.

• | An intermittent TP sensor output will cause the system to go rich due to a false indication of the engine accelerating.

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

• | Loose terminal connection

- | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

• | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

• | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

### Test Description

The numbers below refer to the step numbers on the Diagnostic Table:

1. DTCs other than P0172 may indicate a condition present which may cause a lean condition. If this is the case, repairing the condition which caused the other DTC will most likely correct the DTC P0172.

2. If the DTC P0172 test passes while the Fail Records conditions are being duplicated, the rich condition is intermittent. Refer to Diagnostic Aids for additional information on diagnosing intermittent conditions.

#### DTC P0172 - Fuel Trim System Rich

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Are any DTCs set other than P0172? | -- | Go to applicable DTC table | Go to Step 3
3 |

1. Start and run vehicle in closed loop.
2. Observe L.T. FUEL TRIM and S.T. FUEL TRIM display on the scan tool data list.

Are the displayed values at or near the specified values?

• | L.T. FUEL TRIM is the first specified value.

• | S.T. FUEL TRIM is the second specified value.

-23%

-11%

Go to Step 5

Go to Step 4

4 |

1. Review and record the scan tool Fail Records data.
2. Clear the DTC P0172 and operate the vehicle to duplicate the Fail Records conditions.
3. Monitor the scan tool Specific DTC info for DTC P0172 while operating the vehicle to duplicate the Fail Records conditions.
4. Continue operating the vehicle until the DTC P0172 test runs and note test result.

Does the scan tool indicate DTC P0172 failed this ignition?

--

Go to Step 5

Go to Diagnostic Aids

5 | Visually and physically inspect the air filter element and replace it if necessary. Refer to Air Filter Element Replacement . Did the air filter require replacement? | -- | Go to Step 21 | Go to Step 6
6 | Visually and physically inspect the air intake duct for being collapsed or restricted and repair if necessary. Did your inspection reveal a condition requiring repair? | -- | Go to Step 21 | Go to Step 7
7 | Inspect the throttle body inlet screen for damage or for the presence of foreign objects which may partially block airflow through the screen and correct any problem found. Did your inspection of the throttle body reveal a condition requiring repair or replacement? | -- | Go to Step 21 | Go to Step 8
8 | Start the engine and note the idle quality. Is a low or unsteady idle being experienced? | -- | Go to Step 9 | Go to Step 11
9 | With the engine idling, observe the IAC display on the scan tool. Is IAC value less than the specified value? (Value is displayed in counts). | 100 counts | Go to Step 11 | Go to Step 10
10 |

1. Turn the ignition OFF.
2. Physically inspect the throttle body bore, throttle plate, and IAC passages for coking and foreign objects.
3. If a problem was found, repair as necessary.

Did your inspection reveal a condition requiring repair?

--

Go to Step 21

Go to Step 11

11 |

1. Perform the Idle Air Control (IAC) Valve System Check. Refer to Idle Air Control (IAC) System Diagnosis .
2. If a problem is found, repair as necessary.

Did the System Check isolate a problem requiring repair?

--

Go to Step 21

Go to Step 12

12 |

1. Disconnect the vacuum hose from the fuel pressure regulator and inspect the hose for the presence of fuel.
2. If fuel is present in the vacuum hose, replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement .

Did the fuel pressure regulator require replacement?

--

Go to Step 21

Go to Step 13

13 |

1. Turn the ignition ON, engine OFF.
2. Monitor the TP angle display on the scan tool while slowly depressing the accelerator pedal.

Does the TP angle display increase steadily and evenly from minimum value at closed throttle to maximum value at wide open throttle?

0%-100%

Go to Step 14

Go to Step 19

14 |

1. Disconnect the MAF sensor electrical connector.
2. Operate the vehicle in Closed Loop while monitoring the L.T. FUEL TRIM and S.T. FUEL TRIM display on the scan tool.

Did both values change to near the specified value?

0%

Go to Step 20

Go to Step 15

15 |

1. Perform Fuel System Pressure Test.
2. If the Pressure Test isolates a problem, repair as necessary. Refer to Fuel System Pressure Test .

Did the Pressure Test isolate a problem requiring repair?

--

Go to Step 21

Go to Step 16

16 |

1. Perform the Evaporative Emissions Control (EVAP) Canister Purge Valve System Check. Refer to Evaporative Emission Control System Diagnosis .
2. If System Check isolates a problem, repair as necessary.

Did the System Check isolate a problem requiring repair?

--

Go to Step 21

Go to Step 17

17 |

1. Perform the Injector Balance Test.
2. Refer to Fuel Injector Balance Test .

Did the Injector Balance Test isolate a problem requiring repair?

--

Go to Step 21

Go to Step 18

18 |

1. Remove and visually/physically inspect the HO2S 1 for silicon contamination. This will be indicated by a powdery white deposit on the portion of the HO2S that is exposed to the exhaust stream.
2. If contamination is evident on the HO2S, replace contaminated sensor. Refer to Heated Oxygen Sensor Replacement .

Did the sensor require replacement?

--

Go to Step 21

Go to Diagnostic Aids

19 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the action complete? | -- | Go to Step 21 | --
20 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Is the action complete? | -- | Go to Step 21 | --
21 |

1. Review and record the scan tool Fail Records data.
2. Clear the DTC P0172 and operate the vehicle to duplicate the Fail Records conditions.
3. Monitor the scan tool Specific DTC info for DTC P0172 while operating the vehicle to duplicate the Fail Records conditions.
4. Continue operating the vehicle until the DTC P0172 test runs and note test result.

Does the scan tool indicate DTC P0172 failed this ignition?

--

Go to Step 2

System OK