For 1990-2009 cars

### Circuit Description

In order 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 PCM monitors the bank 1 HO2S 1 and bank 2 HO2S 1 signals 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%; if the HO2S signals are indicating a lean condition the PCM will add fuel, resulting in fuel trim values above 0%. If a rich condition is detected, the fuel trim values will be below 0%, indicating that the PCM is reducing the amount of fuel delivered. If an excessively rich condition is detected on bank 1, the PCM will set DTC P0172. The PCM s maximum authority to control long term fuel trim allows a range between -23% and +16%. The PCM s maximum authority to control short term fuel trim allows a range between -11% and +20%. 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 weighted (assigned a percentage of importance in determining the total fuel trim status for the diagnostic) as follows:

Manaul Transaxle

• | Idle, purge commanded (Cell 10 - approximately 27%)

• | Normal driving, purge commanded (Cell 2 - approxmately 18%)

• | Acceleration, purge commanded (Cell 3 - approximately 9%)

• | High Flow, purge commanded (Cell 4 - approximately 9%)

• | Normal driving, no purge commanded (Cell 6 - approximately 27%)

• | Acceleration, no purge commanded (Cell 7 - approximately 9%)

Automatic Transaxle

• | Idle, purge commanded (Cell 10 - approximately 15%)

• | Normal driving, purge commanded (Cell 2 - approxmately 25%)

• | Deceleration, no purge commanded (Cell 5 - approximately 5%)

• | Normal driving, no purge commanded (Cell 6 - approximately 40%)

• | Idle, no purge commanded (Cell 9 - approximately 5%)

### Conditions for Setting the DTC

• | No TP sensor, EVAP system, HO2S, misfire, IAT sensor, MAP sensor, Idle speed, fuel injector(s), IC/Bypass, EGR Pintle, EGR Flow, ECT sensor, CKP sensor, CMP sensor, or MAF sensor DTCs are 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 15 kPa and 85 kPa.

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

• | 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.

• | Bank 1 Long term fuel trim is at or near maximum authority of -23%

• | Bank 1 Short term fuel trim is at or near maximum authority of -11%.

• | All conditions have been met in the Fuel Trim Cells.

### Action Taken When the DTC Sets

• | The PCM will illuminate the 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 Fail Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn the MIL OFF 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 Clear Information function or by disconnecting the PCM battery feed.

### Diagnostic Aids

Check 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 injector(s) faulty - Refer to Fuel Injector Balance Test .

• | Check the EVAP Canister for Fuel Saturation. If the EVAP Canister is full of fuel, check canister control and hoses. Refer to Evaporative Emission Control System Diagnosis .

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

• | Check for a leaking fuel pressure regulator diaphragm by checking the vacuum line to the fuel pressure regulator for the presence of fuel. If there is fuel in the vacuum line, refer to Fuel Pressure Regulator Replacement .

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

• | Poor connection at the PCM - Inspect harness connectors for the following conditions:

- | Backed out terminals.

- | Improper mating.

- | Broken locks.

- | Improperly formed or damaged terminals.

- | Poor terminal to wire connection.

• | Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the affected HO2S display on the scan tool while moving connectors and wiring harnesses related to the engine harness. A change in the display will indicate the location of the fault.

Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.

### Test Description

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

1. DTCs other than P0172 and P0175 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/P0175.

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

#### DTC P0172 - Fuel Trim System Rich Bank 1

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to the Powertrain On Board Diagnostic (OBD) System Check
2 | Are any DTCs set other than P0172 and P0175? | -- | Go to the other DTCs first. | Go to Step 3
3 |

1. Start and run vehicle in closed loop.
2. Observe Bank 1 L.T. Fuel Trim and Bank 1 S.T. Fuel Trim display on the scan tool Eng 1 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/P0175 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 | Is DTC P0175 also set? | -- | Go to Step 6 | Go to Step 18
6 | Visually and physically inspect the air filter element and replace it if necessary. Did the air filter require replacement? | -- | Go to Step 22 | Go to Step 7
7 | 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 22 | Go to Step 8
8 | 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 22 | Go to Step 9
9 | Start the engine 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, observe the Idle Air Control display on the scan tool. Is Idle Air Control value less than the specified value? Value is specified in Counts. | 100 | Go to Step 12 | Go to Step 11
11 |

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

Did your inspection reveal a condition requiring repair?

--

Go to Step 22

Go to Step 12

12 |

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

Did the Idle Air Control (IAC) Valve Check isolate a problem requiring repair?

--

Go to Step 22

Go to Step 13

13 |

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 .

Was the problem found?

--

Go to Step 22

Go to Step 14

14 |

1. Turn ON the ignition switch.
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% to 100%

Go to Step 15

Go to Step 20

15 |

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

Did both values change to near the specified value?

0%

Go to Step 21

Go to Step 16

16 |

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

Did the Fuel System Pressure Test isolate a problem requiring repair?

--

Go to Step 22

Go to Step 17

17 | Perform the EVAP Control System Diagnosis. Refer to Evaporative Emission Control System Diagnosis . If this isolates a problem, repair as necessary. Was a problem found? | -- | Go to Step 22 | Go to Step 18
18 |

1. Perform the Fuel Injector Balance Test.
2. If this isolates a problem, repair as necessary. Refer to Fuel Injector Balance Test .

Did the Fuel Injector Balance Test isolate a problem requiring repair?

--

Go to Step 22

Go to Step 19

19 |

1. Remove and visually/physically inspect the Bank 1 HO2S 1 and the Bank 2 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 Bank 1 or Bank 2 HO2S, replace the contaminated sensor(s).

Did sensors require replacement?

--

Go to Step 22

Go to Diagnostic Aids

20 |

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. Refer to Throttle Position Sensor Replacement .

Is the action complete?

--

Go to Step 22

--

21 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Is the action complete? | -- | Go to Step 22 | --
22 |

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