For 1990-2009 cars

### Circuit Description

The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop the PCM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During Closed Loop the PCM adds HO2S inputs and level of purge to calculate short term and long term fuel trim adjustments. If the HO2S indicates a lean condition, fuel trim values will be above 0 percent . If the HO2S indicates a rich condition, fuel trim values will be below 0 percent. The values for the short term fuel trim change rapidly in response to the HO2S voltage signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term fuel trim diagnostic is based on an average of cells currently being used, but is capable of identifying a rich condition within a single cell. The PCM determines the cell based on the current engine speed and engine load. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition. If the PCM detects an excessively rich condition, DTC P0172 sets.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0172 Fuel Trim System Rich

### Conditions for Running the DTC

• | DTCs P0030, P0036, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0128, P0130-P0138, P0140, P0141, P0201-P0204, P0220, P0222, P0223, P0300, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P0506, P0507, P060D, P060E, P1101, P1106, P1107, P1114, P1115, P1133, P1134, P1380, P1381, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, P2176 are not set.

• | The engine is in Closed Loop status.

• | The engine coolant temperature (ECT) is between -7 and +120°C (+19.4 and +248°F).

• | The intake air temperature (IAT) is between -7 and +145°C (+19.4 and +293°F).

• | The manifold absolute pressure (MAP) is between 15-100 kPa (2.2-14.5 psi).

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

• | The engine speed is between 400-6,100 RPM.

• | The barometric pressure (BARO) is more than 72 kPa (10.4 psi).

• | The mass air flow (MAF) is between 1-512 g/s.

• | The fuel level is more than 10 percent.

• | DTC P0172 runs continuously when the above conditions are met.

### Conditions for Setting the DTC

• | The long term fuel trim weighted average value is less than a calibrated value.

• | The diagnostics have determined that a rich condition was not due to excessive vapor.

• | The above conditions are present for more than 2 minutes.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

• | The current cell can be observed using a scan tool.

• | A malfunctioning MAF sensor can cause a rich condition and set this DTC.

• | If an intermittent condition is suspected , refer to Testing for Intermittent Conditions and Poor Connections .

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Important: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system (TCS) indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators.

Are any DTCs other than DTC P0172 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3 |

1. Turn ON the ignition.
2. Observe the Freeze Frame/Failure Records parameter with a scan tool and record the displayed data for this DTC.
3. Start and operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions observed from the Freeze Frame/Failure Records.
4. Observe the Long Term FT parameter.

Does the scan tool indicate that the long term fuel trim is less than the specified value?

-18%

Go to Step 4

Go to Diagnostic Aids

4 | Slowly operate the engine from idle to 3,000 RPM while observing the HO2S 1 and HO2S 2 parameters with a scan tool. Does the scan tool indicate that the heated oxygen sensor (HO2S) voltages are within the specified range and fluctuating? | 200-800 mV | Go to Step 5 | Go to Step 6
5 |

1. Turn OFF the engine.
2. Visually and physically inspect the following items:

• | The inlet screen of the mass air flow (MAF) sensor for blockage--Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

• | The vacuum hoses for splits, kinks , and proper connections--Refer to Emission Hose Routing Diagram .

• | The air intake duct for being collapsed or restricted--Refer to Air Cleaner Resonator and Outlet Duct Replacement .

• | The air filter for being dirty or restricted--Refer to Air Cleaner Element Replacement .

• | Objects blocking the throttle body--Refer to Throttle Body Assembly Replacement .

Did you find and correct the condition?

--

Go to Step 9

Go to Step 8

6 |

1. Turn OFF the engine
2. Visually and physically inspect the following items:

• | The HO2S for proper installation--Refer to Heated Oxygen Sensor 1 Replacement and Heated Oxygen Sensor 2 Replacement .

• | Ensure that the electrical connectors and wires are secured and not contacting the exhaust system.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 7

7 | Test the HO2S high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Fuel System Diagnosis
8 | Inspect for the following:

• | Excessive fuel in the crankcase

• | Saturated evaporative canister, stuck purge valve, or fuel cap not sealing

• | Excessive fuel pressure--Refer to Fuel System Diagnosis .

• | Properly functioning fuel injectors--Refer to Fuel Injector Diagnosis .

• | Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?

--

Go to Step 9

Go to Symptoms - Engine Mechanical

9 | Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.

1. Turn ON the ignition, with the engine OFF.

Important: DO NOT clear codes with the engine running. The codes may reset in the same ignition cycle.

2. Clear the DTCs with a scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. Operate the vehicle within the Conditions for Running in the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 10

10 | To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420. Refer to DTC P0420 . Did you complete the procedure? | -- | Go to Step 11 | Go to DTC P0420
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK