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 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 HO2S inputs are added and used by the ECM to calculate short and long term fuel trim fuel delivery adjustments. If the HO2S indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensor (O2S) indicate a rich condition, fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response to the HO2S signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the ECM detects an excessively lean condition, this DTC sets.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P2177 Fuel Trim System Lean at Cruise or Accel Bank 1 |
| • | DTC P2179 Fuel Trim System Lean at Cruise or Accel Bank 2 |
Conditions for Running the DTC
| • | Before the ECM can report DTC P2177 or P2179 failed, DTC P0101, P0121, P0122, P0123, P0133, P0153, P0221, P0222, P0223, P0336, P0338, P0443, P0458, P0459, P0461, P0462, P0463, P2066, P2067, and P2068 must run and pass. |
| • | The fuel system is in closed loop. |
| • | The long fuel trim is active. |
| • | The engine coolant temperature (ECT) is more than 60°C (140°F). |
| • | The evaporative emission (EVAP) canister purge solenoid valve is not enabled. |
| • | The intake air temperature (IAT) is less than 60°C (140°F). |
| • | The fuel level is more than 11.6 percent. |
| • | The amount of air flow into the engine is more than 7 000 grams. |
| • | DTCs P2177 and P2179 run continuously once the above conditions are met for at least 300 seconds. |
Conditions for Setting the DTC
| • | The Total Fuel Trim Avg. is more than 23 percent. |
| • | The condition exists for 4 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) at the beginning of the fourth ignition cycle, after 3 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 and related Freeze Frame data clears after 40 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
| • | A fuel system delivery condition causes this DTC to set. Thoroughly inspect all items that cause a lean condition. |
| • | Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if there is a current condition.
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If DTC P2177 and P2179 is set at the same time, this indicates that both banks of the engine are operating lean. Inspect for items that would cause both banks of the engine to operate lean.
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Disconnecting the mass air flow (MAF) sensor determines if the MAF sensor signal is skewed. If the Short Term FT parameter changes more than the specified value, there is a condition with the MAF sensor. A MAF sensor condition can cause this DTC without setting a MAF DTC. If there is a MAF sensor condition, the MAF sensor parameters will appear to be within range.
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A vacuum leak causes DTC P2177 and P2179 to set at the same time. Inspect all areas of the engine for a vacuum leak. Also inspect the positive crankcase ventilation (PCV) valve for being the correct one for this application. Make sure that the engine oil fill cap is in place and that it is tight. Verify that the engine oil dip stick is fully seated.
Step | Action | Values | Yes | No | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||||||||||||
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Important: If any DTCs are set, except P2177 or P2179 , refer to those DTCs before proceeding with this diagnostic.
Is the Total Fuel Trim Avg. less than the specified value indicated? | 23% | Go to Step 3 | Go to Step 4 | |||||||||||||||||||
3 |
Does the DTC fail this ignition cycle? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||||||||
Are both banks of the engine operating lean? | -- | Go to Step 5 | Go to Step 7 | |||||||||||||||||||
Important: Additional DTCs set with the mass air flow (MAF) sensor disconnected. Does the Short Term FT parameter for both banks of the engine change more than the specified value with the MAF sensor disconnected? | 20% | Go to DTC P0101 | Go to Step 6 | |||||||||||||||||||
Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 8 | Go to Fuel System Diagnosis | |||||||||||||||||||
7 | Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 8 | Go to Diagnostic Aids | ||||||||||||||||||
8 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 9 | ||||||||||||||||||
9 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
