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 Loop 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 the short and long term fuel trim adjustments. If the HO2S indicates a lean condition, the fuel trim values will be greater than 0 percent. If the HO2S indicates a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the HO2S voltage signals. The long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1 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. This DTC is continuously monitored during engine operation. 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 P0013, P0014, P0016, P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0125 , P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0201-P0206, P0220, P0300, P0301-P0306, P0326, P0327, P0341, P0446, P0483, P0496, P0502, P0503, P0506, P0507, P0601, P0602, P0604, P0606, P0641, P0651, P1133, P1516, P1680, P2101, P2120, P2125, P2135, P2138, P2176 are not set. |
| • | The engine is in a Closed Loop status. |
| • | The engine coolant temperature (ECT) is 60-125°C (140-257°F). |
| • | The intake air temperature (IAT) is -25°C to +150°C (-13°F to +302°F). |
| • | The manifold absolute pressure (MAP) is more than 26 kPa (3.8 psi). |
| • | The vehicle speed is less than 132 km/h (82 mph). |
| • | The engine speed is between 400-5,850 RPM. |
| • | The barometric pressure (BARO) is more than 70 kPa (10.2 psi). |
| • | The fuel level is more than 10 percent. |
| • | DTC P0172 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
| • | The average long term fuel trim value is below -35 percent. |
| • | The diagnostics have determined that a rich condition was not due to excessive vapor. |
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
| • | Fuel contamination, such as water and alcohol, will affect the fuel trim. |
| • | The system will go rich if the injectors are supplying too much fuel. |
| • | Using the scan tool, review the Failure Records. If an intermittent condition is suspected , refer to Intermittent Conditions . |
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||||
2 | Are any DTCs other than P0172 also set? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 3 | ||||||||||
3 |
Is the Long Term FT parameter less than the specified value? | -35% | Go to Step 4 | Go to Diagnostic Aids | ||||||||||
4 |
Does the scan tool indicate that the values are within the specified range and fluctuating? | 200-800 mV | Go to Step 5 | Go to Step 6 | ||||||||||
5 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 | ||||||||||
6 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Fuel System Diagnosis | ||||||||||
7 | Inspect for the following:
Did you find and correct the condition? | -- | Go to Step 8 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||||
8 |
Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim. Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 9 | ||||||||||
9 | Observe the Capture Info with a scan tool. Have any other DTCs not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
