Description
This diagnostic monitors the operation of the air/fuel ratio feedback controls. In order to provide the best possible combination of driveability, fuel economy, and emission control, the powertrain control module (PCM) uses a Closed Loop air/fuel metering system. The PCM monitors the heated oxygen sensor (HO2S) input and when in Closed Loop adjusts fuel delivery based on the HO2S information. Changes in fuel delivery will be indicated by the long term and the short term fuel trim values that are displayed on the scan tool. The ideal fuel trim value is around 0 percent. The PCM will add fuel when the heated oxygen sensor signal is indicating a lean condition. Additional fuel is indicated by fuel trim values that are above 0 percent. The PCM will reduce the amount of fuel delivered when a rich condition is indicated by the HO2S. Fuel trim values below 0 percent indicate a reduction in fuel. If the PCM detects that the long term fuel trim is more than a predetermined value, this DTC sets.
DTC Descriptors
This diagnostic procedure supports the following DTCs.
| • | DTC P0171 HO2S Fuel Trim System Lean Bank 1 |
| • | DTC P0174 HO2S Fuel Trim System Lean Bank 2 |
HO2S Indication | Short Term FT Action | Long Term FT Action | Short Term FT Response |
|---|---|---|---|
Lean Condition | Quick Increase of 1% or More | Slow Increase of 1% or More | Return to 0% |
Desired Condition | Stays Near 0% | Stays at Learned +/- Value | Stays Near 0% |
Rich Condition | Quick Decrease of -1% or Less | Slow Decrease of -1% or Less | Return to 0% |
Conditions for Running the DTC
| • | Before the PCM can report that DTC P0171 or P0174 failed, DTC P0442 must run and pass. |
| • | DTCs P0030, P0050, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0135, P0155, P0300-P0306, P0335, P0339, P0401, P0404, P0442, P0443, P0496, P1128, P1129, P2227, P2228, P2229, P2413, P2414, and P2415 are not set. |
| • | Engine coolant temperature (ECT) is more than 69°C (156°F). |
| • | Intake air temperature (IAT) is at least 0°C (32°F). |
| • | Manifold absolute pressure (MAP) is at least 24 kPa. |
| • | Engine speed is between 630-4,000 RPM. |
| • | The engine is operating in CLOSED LOOP. |
| • | The evaporative emission (EVAP) monitor is not running. |
| • | DTC P0171 and DTC P0174 run once per drive cycle when the above conditions are met. |
Conditions for Setting the DTC
The long term fuel trim of bank 1 or bank 2 is more than 18 percent.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | Inspect for a contaminated oxygen sensor. If contamination is found, determine the cause and correct the condition before replacing the HO2S. |
| • | Inspect for a damaged wiring harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the heated oxygen sensor (HO2S) bank 1 sensor 1 display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the display will indicate the location of the fault. |
| • | Inspect for fuel contamination--Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | Test for the correct fuel pressure--The fuel system will be lean if the fuel pressure is too low or the fuel filter is restricted. In order to determine the cause of DTC P0171 or DTC P0174 monitoring the fuel pressure while driving the vehicle at various road speeds may be necessary. Refer to Fuel System Diagnosis . |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step determines whether the fault is present.
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If DTC P0171 and P0174 are set at the same time, this indicates both banks of the engine are operating lean. Inspect the items that would cause both banks to operate lean.
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A vacuum leak causes DTC P0171 and P0174 to set at the same time. Inspect all areas of the engine for a vacuum leak. Also inspect the 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.
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This step tests for inadequate fuel delivery from a fuel injector. The fault may be a fuel injector or the fuel injector electrical circuit.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||||
|
Important: If any DTCs are set, except P0171 and P0174, refer to those DTCs before proceeding with this diagnostic.
Does the scan tool display less than the specified value? | 18% | 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 6 | |||||||||||
Visually and physically inspect for any of the following conditions:
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7 | |||||||||||
6 | Visually and physically inspect for any of the following conditions:
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7 | ||||||||||
7 |
Important: When you have completed the fuel system diagnosis, return to this diagnostic. Test fuel system for operating lean. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 | ||||||||||
Test the fuel injectors for any of the following conditions:
Did you find and correct a condition? | -- | Go to Step 11 | Go to Step 9 | |||||||||||
9 | Test for an intermittent and for a poor connection at the appropriate HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 | ||||||||||
10 | Replace the HO2S. Refer to the appropriate procedure: Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||||
11 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 12 | ||||||||||
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
