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

• | DTCs 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, P0503, P0506, P0507, P0601, P1133, P1336, P1404, and P1441 are not set.

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

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

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

• | The vehicle speed is below 70 mph (113 km/h).

• | The MAP is above 27 kPa.

• | The BARO is greater than 74 kPa.

• | The EVAP purge is not occurring.

• | The Fuel Trim Index is below 75 (-54 percent).

• | The above conditions are present for 4 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

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool 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 injector can cause a rich condition and set DTC P0172. Refer to Fuel Injector Solenoid Coil Test for further diagnosis.

4. A loose TP sensor may not set a TP sensor related DTC, but may 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 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Are any component related DTCs set? | -- | Go to Component DTC table | Go to Step 3
3 |

1. Turn the ignition switch ON, with the engine running.
2. Operate the vehicle while in Closed Loop .

Is the Fuel Trim Index above the specified value?

75

Go to Step 4

Go to Step 5

4 |

1. Turn the ignition switch ON, with the engine OFF.
2. Review the Freeze Frame data and note the parameters.
3. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting The DTC as noted.

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

75

Go to Step 21

Go to Step 5

5 |

1. Visually and physically check the air cleaner filter element for excessive dirt or being plugged.
2. Replace if necessary.

Did the air cleaner filter require replacement?

--

Go to Step 21

Go to Step 6

6 |

1. Visually and physically check the air intake system for being collapsed or restricted.
2. Repair if necessary

Did the air intake system require repair?

--

Go to Step 21

Go to Step 7

7 | Inspect the throttle body inlet for damage or foreign objects which may partially block the airflow and correct any problem found. Did the inspection of the throttle body reveal a condition requiring a repair or replacement? | -- | Go to Step 21 | Go to Step 8
8 |

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

Did the inspection reveal a condition requiring a repair?

--

Go to Step 21

Go to Step 9

9 | Start the engine with the vehicle in park or neutral and A/C OFF and note the idle quality. Is a low or unsteady idle being experienced? | -- | Go to Step 10 | Go to Step 12
10 | With the engine idling. Are the IAC counts below the specified value? | 100 | Go to Step 12 | Go to Step 11
11 |

1. Disconnect the MAP sensor electrical connector.
2. Operate the vehicle while in Closed Loop.

Does the Fuel Trim Index increase above the specified value?

60

Go to Step 20

Go to Step 12

12 |

1. Refer to DTC P0506 Idle Speed Low or DTC P0507 Idle Speed High to check the IAC valve performance.
2. If a problem is found, repair 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 and inspect the hose for spits, restrictions, or 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 inspection reveal a condition requiring a repair?

--

Go to Step 21

Go to Step 14

14 |

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

Does the throttle position display increase steadily and evenly from its minimum voltage at closed throttle to its 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 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 as necessary.

Was a problem isolated that requiring a repair?

--

Go to Step 21

Go to Step 17

17 |

1. Perform the Fuel Injector Solenoid Coil Test and Fuel Injector Balance Test .
2. If the table isolates a problem, repair as necessary.

Did the table isolate a problem requiring a repair?

--

Go to Step 21

Go to Step 18

18 |

1. Remove and visually/physically inspect the O2S 1 for silicon contamination. This will be indicated by a powdery white deposit on the portion of the O2S 1 sensor exposed to the exhaust stream.
2. If contamination is present on the O2S 1 sensor, find the source of the contamination and repair and also replace the contaminated O2S 1 sensor.

Was contamination present?

--

Go to Step 21

Go to Diagnostic Aids

19 |

1. Check the TP sensor mounting screws and tighten or replace them as necessary, if they are loose or missing.
2. If the screws are OK, replace the TP sensor.

Is the action complete?

--

Go to Step 21

--

20 | Replace the MAP sensor. Is the action complete? | -- | Go to Step 21 | --
21 |

1. Using the scan tool, clear the DTCs.
2. Start the engine and idle at normal operating temperature.
3. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

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

--

Go to Step 22

Go to Step 2

22 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK