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 (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicate a lean condition, the FT values will be above 0 percent. If the HO2S indicate a rich condition, the FT values will be below 0 percent. The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain an Air/Fuel Ratio of 14.7:1. The FT 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. 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 FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and load. If the ECM detects an excessively rich condition, DTC P0172 sets.
This diagnostic procedure supports the following DTC:
DTC P0172 Fuel Trim System Rich
• | DTCs P0030, P0036, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0201-P0204, P0220, P0222, P0223, P0300, P0411, P0412, P0418, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P0506, P0507, P1106, P1107, P1114, P1115, P1133, P1134, P1516, P1680, P1681, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, P2176, P2430, P2431, P2432, P2433, P2440, P2444 are not set. |
• | The engine is in CL 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 mass air flow (MAF) is between 1-512 g/s. |
• | 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 fuel level is more than 10 percent. |
• | DTC P0172 runs continuously once the above conditions have been met. |
• | The long term FT weighted average value is less than a calibrated value. |
• | The above condition is present for more than 2 minutes. |
• | 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. |
• | 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. |
• | Fuel contamination, such as water and alcohol, will affect the FT. |
• | 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 Testing for Intermittent Conditions and Poor Connections . |
The number below refers to the step number on the diagnostic table.
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 DTC P0172 also set? | -- | Go to Step 3 | |||||||||||
3 |
Is the Long Term FT parameter less than the specified value? | -18% | 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? | 20-900 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 | ||||||||||
Inspect for the following:
Did you find and correct the condition? | -- | Go to Step 9 | ||||||||||||
9 |
Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
Important: DO NOT clear the 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 | In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the Conditions for Running and setting DTC P0420, and verify that DTC P0420 runs and passes. Refer to DTC P0420 . Does the DTC run and pass? | -- | 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? | -- | System OK |