Circuit Description
The engine control module (ECM) 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 ECM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During Closed Loop, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim adjustments. If the HO2S indicate a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicate 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 ECM 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 P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123 , P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0201-P0204, P0220, P0300, P0301-P0304, P0336, P0340, P0341, P0442, P0446, P0452, P0453, P0455, P0481, P0496, P0502, P0506, P0601, P0602, P0604, P0606, P060D, P060E, P062F, P0641, P0651, P0700, P1133, P1516, P1621, P2101, P2120, P2125, P2135, P2138, P2176 are not set. |
| • | The engine is in Closed Loop status. |
| • | The engine coolant temperature (ECT) is between 60-125°C (140-257°F). |
| • | The intake air temperature (IAT) is between -25 to +150°C (-13 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 400-5,700 RPM. |
| • | The barometric pressure (BARO) is more than 72 kPa (10.4 psi). |
| • | DTC P0172 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
| • | The average long term fuel trim value is below -36 percent. |
| • | The above condition is present for 16 seconds. |
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 effect the fuel trim. |
| • | The system will go rich if the injectors are supplying too much fuel. |
| • | Use a scan tool in order to review the Failure Records. 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 | |||||||||||
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 P0172 also set? | -- | Go to Step 3 | |||||||||||
3 |
Is the Long Term FT less than the specified value? | -36% | Go to Step 4 | Go to Diagnostic Aids | ||||||||||
4 |
Is the MAP sensor parameter within the specified range? | 19-42 kPa | Go to Step 5 | Go to DTC P0106 | ||||||||||
5 |
Does the scan tool indicate that the values are within the specified range and fluctuating? | 200-800 mV | Go to Step 6 | Go to Step 7 | ||||||||||
6 |
Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 | ||||||||||
7 |
Did you find and correct the condition? | -- | Go to Step 9 | Go to Fuel System Diagnosis | ||||||||||
8 | Inspect for the following:
Did you find and correct the condition? | -- | Go to Step 9 | |||||||||||
9 |
Important: DO NOT clear codes with the engine running. The codes may reset in the same ignition cycle. 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 | -- | ||||||||||
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
