Troubleshooting
DTC P0174 System too Lean (Bank 2)CIRCUIT DESCRIPTION
DTC Detecting Condition:
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim includes the short-term fuel trim and the long-term fuel trim.
The short-term fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at its ideal theoretical value. The signal from the A/F sensor is approximately proportional to the existing air-fuel ratio, and ECM comparing it with the ideal theoretical value, the ECM reduces fuel volume immediately if the air-fuel ratio is rich and increases fuel volume if it is lean. The long-term fuel trim compensates the deviation from the central value of the short- term fuel trim store up by each engine tolerance, and the deviation from the central value due to the passage of time and changes of using environment. If both the short-term fuel trim and the long-term fuel trim exceed a certain value, it is detected as a malfunction and the MIL lights up.
HINT:
- When the DTC P0171 or P0174 is recorded, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 is recorded, the actual air-fuel ratio is on the rich side.
- If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 or P0174 is recorded. The MIL then comes on.
- If the total of the short-term fuel trim value and the long-term fuel trim value is within ±35% (80 °C (176 °F) or more), the system is functioning normally.
- The A/F sensors (bank 1, 2 sensor 1) output voltage and the short-term fuel trim value can be read using the OBD II scan tool or hand-held tester.
- The ECM controls the voltage of AFR+, AFL+, AFR- and AFL- terminals of ECM to the fixed voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without OBD II scan tool or hand-held tester.
- OBD II scan tool (excluding hand-held tester) displays the one fifth of the A/F sensors (bank 1, 2 sensor 1) output voltage which is displayed on the hand-held tester.
MONITOR DESCRIPTION
Monitor Description:
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
Under closed-loop fuel control, fuel injection amounts that deviate from the ECM's estimated fuel amount will cause a change in the long-term fuel trim compensation value. This long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. And the deviation from the simulated fuel injection amount by the ECM affects a smoothed fuel trim learning value. The smoothed fuel trim learning value is the combination of smoothed short-term fuel trim (fuel feedback compensation value) and smoothed long-term fuel trim (learning value of the air-fuel ratio). When the smoothed fuel trim learning value exceeds the DTC threshold, the ECM interprets this as a fault in the fuel system and sets a DTC.
Example:
The smoothed fuel trim leaning value is more than +35% or less than -35%. The ECM interprets this as a failure in the fuel system.
Wiring Diagram:
Step 1 - 5:
Step 6 - 8:
Step 8 (Continued):
Step 8 (Continued) - 13:
Step 13 (Continued) - 18:
INSPECTION PROCEDURE
HINT: Read freeze frame data using OBD II scan tool or hand-held tester, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.
CONFIRMATION DRIVING PATTERN
Confirmation Driving Pattern:
1. Connect the hand-held tester to the DLC3.
2. Switch the hand-held tester from normal mode to check mode .
3. Start the engine and warm it up for 2 min. or more with all accessory switches OFF.
4. Drive the vehicle at 60 - 120 km/h (38 - 75 mph) and engine speed at 1,600 - 3,200 rpm for 3 - 5 minutes
HINT: If a malfunction exists, the MIL will light up during step (4).
NOTE: If the conditions in this test are not strictly followed, detection of the malfunction will impossible. If you do not have a hand-held tester, turn the ignition switch OFF after performing steps(3) and (4), then perform steps (3) and (4) again.
CHECK FOR INTERMITTENT PROBLEMS
Hand-held tester only:
Inspect the vehicle's ECM using check mode. Intermittent problems are easier to detect when the ECM is in check mode with hand-held tester. In check mode, the ECM uses 1 trip detection logic, which has a higher sensitivity to malfunctions than normal mode (default), which uses 2 trip detection logic.
a. Clear the DTC.
b. Set the check mode.
c. Perform a simulation test.
d. Check the connector and terminal.
e. Wiggle the harness and connector.