P0174
DTC P0174
CIRCUIT DESCRIPTION
The powertrain control module (PCM) 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 PCM determines fuel delivery based on sensor signals without oxygen sensor input. During Closed Loop the PCM adds oxygen sensor inputs and level of purge to calculate Short and Long Term fuel trim adjustments. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. The values for the Short Term fuel trim change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term fuel trim makes coarse adjustments in order to maintain an Air/Fuel Ratio of 14.7:1. 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 fuel trim diagnostic is based on an average of cells currently being used. The PCM selects the cells based on the engine speed and engine load. If the PCM detects an excessively lean condition, DTC P0174 sets.
DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0174 Fuel Trim System Lean Bank 2
CONDITIONS FOR RUNNING THE DTC
- DTCs P0050, P0056, P0059, P0060, P0068, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0120, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0300, P0401, P0403, P0404, P0405, P0406, P0430, P0442, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0462, P0463, P0464, P0506, P0507, P1153, P1154, P1404, P1516, P2101, P2107, P2108, P2119, P2120, P2125, P2135, P2138, P2A03, P2A04 are not set.
- The engine is in Closed Loop status.
- Fuel Trim Learn is enabled.
- The engine coolant is between 38.5-121°C (101.3-250°F).
- The intake air temperature (IAT) is between -38.5 and +140°C (-37.3 and +284°F).
- The manifold absolute pressure (MAP) is between 15-99 kPa (2.1-28.8 psi).
- The vehicle speed is less than 132 km/h (82 mph).
- The engine speed is between 525-5,600 RPM.
- The barometric pressure (BARO) is more than 70 kPa (10.1 psi).
- The idle purge is enabled.
- The mass air flow (MAF) is between 1-150 g/s.
- The fuel level is more than 10 percent.
- The scan tool special functions are not active.
CONDITIONS FOR SETTING THE DTC
- The average Long Term fuel trim is above 18.8 percent.
- The above condition is present for more than 2 minutes.
- This diagnostic runs continuously.
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
- The system will go lean if an injector is not providing enough fuel.
- A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel.
- Excessive resistance in the ignition 1 voltage and/or the fuel injector circuits may cause the following symptoms:
- A lean condition
- Misfire
- Rough idle
- Fuel contamination, such as water and alcohol, will effect the fuel trim.
- Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics
- This DTC may set due to poor idle characteristics as a result of uncontrolled fueling caused by an open or high resistance in the HO2S 1 low signal circuit. Before replacing any component, ensure that this condition does not exist.
TEST
