Circuit Description
To provide the best possible combination of driveability, fuel economy and emission control, a Closed Loop air/fuel metering system is used. While in Closed Loop, the PCM monitors the heated oxygen sensor signal voltage and adjust fuel delivery based on signal voltage. A change made to fuel delivery will be indicated by the long term and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim values are around 0%; if heated oxygen sensor signal is indicating a lean condition, the PCM will add fuel, resulting in a fuel trim above 0%, 100% is maximum lean. If a rich condition is detected, the fuel trim values will be below 0%, -99% is maximum rich, indicating that the PCM is reducing the amount of fuel delivered. If an excessively lean condition is detected, the PCM will set DTC P0171.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0121, P0122, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0143, P0144, P0146, P0151, P0154, P0562, P0163, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0300, P0325, P0327, P0340, P0401, P0506, P0507, P1121, P1133, P1153, P1154, P1441, P1442, P1508 and P1509 are not set |
| • | Closed loop enabled. |
| • | Engine Coolant Temperature between 84.5°C (184°F) and 105°C (221°F). |
| • | Barometric Pressure greater than 70.8 kPa. |
| • | Mass Air Flow between 3 and 200 grams per second. |
| • | Manifold Absolute Pressure between 27 and 103.2 kPa. |
| • | Intake Air Temperature between -40°C (-40°F) and 151°C (304°F). |
| • | Engine speed between 400 and 3000 RPM. |
| • | Throttle angle less than 19.8%. |
| • | Vehicle speed less than 82 mph. |
| • | EVAP canister purge tank not full (PCM estimation). |
| • | Fuel trim cells greater than 1.04 for short term and greater than 1.12 for long term. |
Conditions for Setting the DTC
The PCM detects the average fuel trim cell values are greater than 1.04 for short term fuel trim and 1.12 for long term fuel trim for 2.5 seconds.
Action Taken When the DTC Sets
| • | The PCM will illuminate the Malfunction Indicator Lamp (MIL) after two consecutive drive trips that the diagnostic runs and fails. |
| • | The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Freeze Frame and Failure Records. |
| • | A first failure of this DTC will store in Last Test Failed but not History. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A Last Test Failed DTC will clear when the diagnostic runs and does not fail. |
| • | A History DTC will clear after forty consecutive warm-up cycles with no failures of any diagnostic test. |
| • | Use a scan tool to clear DTCs. |
| • | Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation. |
Diagnostic Aids
If the scan tool indicated the test ran and passed, the fault is not present. If the scan tool indicated that the test did not run, ensure that all the test conditions were met.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
Determines whether the fault is present.
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Freeze frame data will aid in locating a hard to find malfunction. For example, if the fault only occurs at high speed, this would be determined by monitoring the fuel trim cells. The fuel trim cell for cruise could be above 95%, which indicates a lean condition. The freeze frame will also indicate how many miles ago the condition was present.
-
If DTC P0174 is also set indicates both banks are operating lean. Inspect items that would cause both banks to operate lean.
Step | Action | Value(s) | Yes | No | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||
2 | Connect a scan tool. Are any DTCs other than P0171 and P0174 set? | -- | Diagnose other DTCs first | |||||||||||||||
Are either values less than their specified value? | 85°C (185°F) 95% LT 98% ST | |||||||||||||||||
Has this diagnostic test ran and failed this ignition cycle? | -- | Refer to Diagnostic Aids | ||||||||||||||||
Is DTC P0174 also set? | -- | |||||||||||||||||
6 | Visually/physically inspect the following items:
Was a problem found in any of the above areas? | -- | Refer to Fuel System Diagnosis | |||||||||||||||
7 | Visually/physically inspect the following items:
Was a problem found in any of the above areas? | -- | Refer to Fuel System Diagnosis | |||||||||||||||
8 | Repair or replace any faulty items found. Is the repair completed? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
