For 1990-2009 cars

### System Description

A Closed Loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy, and emission control. While in Closed Loop operation, the PCM monitors the oxygen sensor signal voltage and adjusts the fuel delivery based upon the signal voltage. The long term fuel trim values and the short term fuel trim values can indicate any changes to the fuel delivery. Monitor the scan tool for these changes. The ideal fuel trim values are around 128 (0 percent). If the oxygen sensor signal indicates a lean condition, the PCM will add fuel resulting in fuel trim values above 128 (0 percent to 100 percent). If you detect a rich condition, the fuel trim values will be below 128 (0 percent to -100 percent), indicating that the PCM is reducing the amount of fuel delivered. If the exhaust emissions reach an excessive level due to a lean or a rich condition, a fuel trim DTC is set.

### Conditions for Running the DTC

• | The following DTCs are not set: P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0201, P0202, P0203, P0204, P0300, P0325, P0335, P0341, P0342, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, and P1441.

• | The intake air temperature (IAT) is between -25°C and 115°C (-13°F- 175°F).

• | The engine coolant temperature (ECT) is between 60°C and 115°C (140°F - 239°F).

• | The engine speed is between 550 RPM and 3400 RPM.

• | The vehicle speed is less than 116 km/h (72 mph).

• | The manifold absolute pressure (MAP) is more than 26 kPa.

• | The barometric pressure (BARO) is more than 72 kPa.

• | An EVAP purge is not occurring.

### Conditions for Setting the DTC

• | The Fuel Trim Index is less than 70 (-46 percent).

• | The above conditions are present for more than 16 seconds.

### Action Taken When the DTC Sets

• | The Malfunction Indicator Lamp (MIL) will illuminate if the fault is active within the same conditions for 2 out of 80 ignition cycles.

| OR:

• | The MIL will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.

• | A history DTC will store.

• | The coolant fan turns on.

### Conditions for Clearing the DTC

• | The MIL turns off after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed.

• | A history DTC clears after 40 consecutive warm up cycles without a fault.

• | Use a scan tool to clear the DTCs.

### Diagnostic Aids

Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the long term fuel trim to 128 (0 percent).

• | Inspect for a poor connection at the PCM. Inspect the harness connectors for the following conditions:

- | Any backed out terminals

- | Any incorrect mating

- | Any broken locks

- | Any incorrectly formed electrical connectors

- | Any damaged terminals

- | A poor terminal-to-wire connection

• | Inspect the wiring harness for damage. If the harness appears to be OK, observe the O2S 1 display on the scan tool while moving the electrical connectors and the wiring harness related to the engine harness. A change in the display will indicate the location of the malfunction.

• | If a DTC P1404 is also set, test the 5 V reference circuits for a short to voltage.

• | Inspect for a restricted intake manifold.

• | Inspect for a restricted exhaust system.

• | A shorted 5 V reference circuit may cause a DTC P0172 to set. Test the 5 V reference sensors for abnormal readings.

### Test Description

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

1. A plugged air cleaner filter element restricts the airflow coming into the engine. This step inspects the condition of the air cleaner filter.

2. A leaky fuel injector can cause a rich condition and set DTC P0172.

3. A loose TP sensor may not set a TP sensor related DTC, but could cause the system to become rich by a higher than actual TP reading.

#### DTC P0172-Fuel Trim System Rich

Step | Action | Values | 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 other DTCs set? | -- | Go to Diagnostic Trouble Code (DTC) List/Type | Go to Step 3
3 | Operate the vehicle in Closed Loop. You may have to drive the vehicle in order to obtain Closed Loop Status. Is the Fuel Trim Index more than the specified value? | -46% | Go to Step 4 | Go to Step 5
4 | Operate the vehicle within the Freeze Frame conditions and the Conditions for Running the DTC as specified in the supporting text. Is the Fuel Trim Index more than the specified value? | -46% | Go to Step 21 | Go to Step 5
5 |

1. Turn off the ignition.
2. Visually and physically inspect the air cleaner element for excessive dirt or foreign objects which may block the airflow. Refer to Air Cleaner Element Replacement .
3. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 6

6 |

1. Visually and physically the air intake system for the following conditions:

• | Any collapsed air ducts

• | Any restrictions

2. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 7

7 |

1. Inspect the following components for damage, blockage, or foreign objects:

• | The throttle bore

• | The throttle plate

• | The IAC passages

2. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 8

8 |

1. Start and idle the engine in Park or Neutral, with the A/C off.
2. Verify the idle quality.

Does the engine have an unsteady idle or a low idle?

--

Go to Step 9

Go to Step 11

9 | Verify the IAC counts with the engine idling. Are the IAC counts less than the specified value? | 100 | Go to Step 11 | Go to Step 10
10 |

1. Turn off the ignition.
2. Disconnect the MAP sensor connector.
3. Start and operate the vehicle in Closed Loop operation. You may have to drive the vehicle in order to get Closed Loop Status.

Does the Fuel Trim Index increase to more than the specified value?

-46%

Go to Step 20

Go to Step 11

11 |

1. Turn off the ignition.
2. Test the IAC valve performance. Refer to DTC P0506 Idle Speed Low and to DTC P0507 Idle Speed High .
3. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 12

12 |

1. Disconnect the vacuum hose from the fuel pressure regulator.
2. Inspect the hose for fuel.
3. If fuel is present, replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 13

13 |

1. Turn on the ignition, leaving the engine off.
2. Use a scan tool in order to monitor the TP sensor angle.
3. Slowly depress the accelerator pedal.

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

--

Go to Step 14

Go to Step 18

14 |

1. Perform the Fuel System Diagnosis .
2. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 15

15 |

1. Perform the Evaporative Emission Control System Diagnosis .
2. If the a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 16

16 |

1. Perform the Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and the Fuel Injector Balance Test .
2. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

17 |

1. Turn off the ignition.

Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.

2. Remove the O2S 1.
3. Visually and physically inspect the O2S 1 for silicon contamination. This contamination will be indicated by a powdery white deposit on the portion of the sensor exposed to the exhaust stream.
4. If contamination is present, find and repair the source of the contamination before replacing the sensor.
5. Replace the O2S 1 sensor. Refer to O2S Replacement .

Did you complete the repair?

--

Go to Step 21

Go to Diagnostic Aids

18 |

1. Turn off the ignition.
2. Inspect the TP sensor for the following conditions:

• | Any loose or missing screws

• | A poor connection

3. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 19

19 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the repair? | -- | Go to Step 21 | --
20 |

1. Turn off the ignition.
2. Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement .

Did you complete the repair?

--

Go to Step 21

--

21 |

1. Use a scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK