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 a Closed Loop operation, the Powertrain Control Module (PCM) monitors the oxygen sensor signal voltage and adjusts the fuel delivery based on 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, or 0 percent. If the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in fuel trim values above 128, that is, from 0 percent to 100 percent. If you detect a rich condition, the fuel trim values will be below 128, or from 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 Setting the DTC

• | DTC's P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0300, P0301, P0302, P0303, P0304, P0325, P0335, P0341, P0342, P0401, P0404, P0405, P0502, P0503, P0506, P0507, P0601, P0602, P1404, P1133, and P1441, not set.

• | Intake Air Temperature (IAT) is between -25°C (-13°F) and 115°C (175°F).

• | Engine Coolant temperature is between 60°C (140°F) and 115°C (239°F).

• | Engine speed is between 550 RPM and 3400 RPM (Auto)

• | Engine speed is between 850 RPM and 3400 RPM (Man)

• | Vehicle speed is below 72 mph (116 km/h).

• | MAP is above 26 kPa.

• | BARO is greater than 72 kPa.

• | EVAP purge is not occurring.

• | Fuel Trim Index is below 70 (-46%).

• | Above conditions present for 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 two out of 80 ignition cycles.

| Or

• | The MIL will illuminate after two 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 MIL/DTC

• | The MIL turns OFF after three consecutive ignition cycles during which the diagnostic runs without a fault present under the Freeze Frame conditions that existed when the DTC failed.

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

• | Clear the MIL/DTCs with a scan tool.

### 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).

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

- | Backed out terminals

- | Improper mating

- | Broken locks

- | Improperly formed electrical connectors

- | 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.

• | Contaminated crankcase

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

• | Check for a restricted intake manifold.

• | Check for a restricted exhaust system.

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

### Test Description

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

1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

2. A clogged air cleaner filter element restricts the airflow coming into the engine. This step checks the condition of the air cleaner filter.

3. A leaky fuel injector can cause a rich condition and set DTC P0172. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) for further diagnosis.

4. 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 | 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 |

1. Turn ON the ignition switch leaving the engine OFF.
2. Install a scan tool.

Are there any component related DTCs set?

--

Go to Component DTC table

Go to Step 3

3 |

1. Start the engine.
2. Allow the engine to reach the normal operating temperature.
3. Operate the vehicle while in a Closed Loop operation.

Is the Fuel Trim Index above the specified value?

-46%

Go to Step 4

Go to Step 5

4 |

1. Turn OFF the engine leaving the ignition switch ON.
2. Review the Freeze Frame data and record the parameters.
3. Start the engine.
4. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting the DTC as specified.

Is the Fuel Trim Index above the specified value while operating under the specified conditions?

-46%

Go to Step 21

Go to Step 5

5 |

1. Turn OFF the ignition switch.
2. Visually and physically check the air cleaner filter element for excessive dirt or for any foreign objects which may block the airflow. Refer to Air Cleaner Element Replacement .
3. Replace the air cleaner filter element if necessary.

Did the air cleaner filter require a replacement?

--

Go to Step 21

Go to Step 6

6 |

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

• | Collapsed

• | Restricted

2. Repair the air intake system if necessary.

Did the air intake system require a repair?

--

Go to Step 21

Go to Step 7

7 |

1. Inspect the throttle body inlet for damage or for any foreign objects which may partially block the airflow.
2. Correct any problem that is present.

Did the inspection of the throttle body reveal a condition requiring a repair or a replacement?

--

Go to Step 21

Go to Step 8

8 |

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

• | Throttle bore

• | Throttle plate

• | IAC passages

2. If a problem is present, repair the problem as necessary.

Did the inspection reveal a condition requiring a repair?

--

Go to Step 21

Go to Step 9

9 |

1. Start the engine with the vehicle in P or N and with the A/C OFF.
2. Verify the idle quality.

Is the engine experiencing a low or an unsteady idle?

--

Go to Step 10

Go to Step 12

10 |

1. Idle the engine.
2. Verify the IAC counts with the engine idling.

Are the IAC counts below the specified value?

100

Go to Step 12

Go to Step 11

11 |

1. Turn OFF the ignition switch.
2. Disconnect the MAP sensor electrical connector.
3. Start the engine.
4. Operate the vehicle while in a Closed Loop operation. (you may have to drive the vehicle to get Closed Loop operation.)

Does the Fuel Trim Index increase above the specified value?

-46%

Go to Step 20

Go to Step 12

12 |

1. Turn OFF the ignition switch.
2. Refer to DTC P0506 Idle Speed Low or DTC P0507 Idle Speed High in order to check the IAC valve performance.
3. If a problem is present, repair the problem as necessary.

Did the inspection reveal a condition requiring a repair?

--

Go to Step 21

Go to Step 13

13 |

1. Disconnect the vacuum hose from the fuel pressure regulator.
2. Inspect the hose for the presence of fuel.
3. If any fuel is present in the vacuum hose, replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement (SFI) .

Did the fuel pressure regulator require a replacement?

--

Go to Step 21

Go to Step 14

14 |

1. Turn ON the ignition switch leaving the engine OFF.
2. Slowly depress the accelerator pedal.

Does the throttle position display increase steadily and evenly from the minimum voltage at closed throttle to the maximum voltage at wide-open throttle?

--

Go to Step 15

Go to Step 19

15 |

1. Perform the Fuel System Diagnosis .
2. If the table isolates a problem, repair the problem as necessary.

Did the table isolate a problem requiring a repair?

--

Go to Step 21

Go to Step 16

16 |

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

Was a problem isolated that required a repair?

--

Go to Step 21

Go to Step 17

17 |

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 the table isolates a problem, repair the problem as necessary.

Did the table isolate a problem requiring a repair?

--

Go to Step 21

Go to Step 18

18 |

1. Turn OFF the ignition switch.
2. Remove and visually/physically inspect the O2S 1 for any silicon contamination. This contamination will be indicated by a powdery white deposit on the portion of the O2S 1 sensor exposed to the exhaust stream.
3. If there is contamination present on the O2S 1 sensor, find the source of the contamination and repair.

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

4. Replace the contaminated O2S 1 sensor. Refer to the Oxygen Sensor Replacement .

Was there contamination present?

--

Go to Step 21

Go to Diagnostic Aids

19 |

1. Turn OFF the ignition switch.
2. Check the TP sensor mounting screws. Tighten or replace the screws if the screws are loose or missing.
3. If the screws are OK, replace the TP sensor. Refer to the Throttle Position Sensor Replacement .

Is the action complete?

--

Go to Step 21

--

20 |

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

Is the action complete?

--

Go to Step 21

--

21 |

1. Clear the DTCs with the scan tool.
2. Start the engine.
3. Idle the engine at the normal operating temperature.
4. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 22

Go to Step 2

22 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK