Troubleshooting
DTC P0174 System Too Lean (Bank 2)CIRCUIT DESCRIPTION
DTC Detection 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 heated oxygen sensor indicates whether the air-fuel ratio is RICH or LEAN compared to the ideal theoretical value, triggering a reduction in the fuel volume if the air-fuel ratio is RICH, and an increase in the fuel volume if it is LEAN.
The long-term fuel trim is the overall fuel compensation carried out in long-term to compensate for a continual deviation of the short-term fuel trim from the central value, due to individual engine differences, wear overtime and changes in the using environment.
If both the short-term fuel trim and the long-term fuel trim are LEAN or RICH beyond a certain value, it is detected as a malfunction and the MIL lights up.
HINT:
- When 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 long-term fuel trim value is within ±25% (75°C) or more, the system is functioning normally.
Wiring Diagram:
Step 1 - 4:
Step 5 - 8:
Step 9 - 11:
Step 12 - 14:
Step 15 - 19:
Step 20 - 21:
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
The narrowing down the trouble area is possible by performing ACTIVE TEST of the following "A/F CONTROL" (heated oxygen sensor or another can be distinguished).
a. Perform ACTIVE TEST by handheld tester (A/F CONTROL).
HINT: "A/F CONTROL" is an ACTIVE TEST which changes the injection volume to -12.5% or +25%.
Case 1 - 4:
1. Connect the hand-held tester to the DLC3 on the vehicle.
2. Turn the ignition switch ON.
3. Warm up the engine with the engine speed at 2,500 rpm for approx. 90 sec.
4. Select the item "DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/A/F CONTROL".
5. Perform "A/F CONTROL" when idle condition (press the right or left button).
Result: Heated oxygen sensor reacts in synchronizing with increase and decrease of injection volume (+25% -> rich output: More than 0.55 V, -12.5% -> lean output: Less than 0.4 V)
NOTE: However, there is a few second delay in the sensor 1 (front sensor) output. And there is about 20 seconds delay in the sensor 2 (rear sensor).
The following procedure of A/F CONTROL enable that to check its output (show its graph indication) of heated oxygen sensor.
To display the graph indication. Select and push the "YES or NO" button 2 data "O2S B1S1 and O2S B1S2" or "O2S B2S1 and O2S B2S2" and press button "4" after selecting "ACTIVE TEST A/F CONTROL/USER DATA".
HINT:
- If different DTCs that are related to different system are output simultaneously while terminal E2 is used as a ground terminal, terminal E2 may be open.
- Read freeze frame data using the hand-held tester or the OBD II scan tool, 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.
- A high heated oxygen sensor (sensor 1) voltage (0.55 V or more) could be caused by a rich air fuel mixture. Check for conditions that would cause the engine to run rich.
- A low heated oxygen sensor (sensor 1) voltage (0.4 V or less) could be caused by a lean air fuel mixture. Check for conditions that would cause the engine to run lean.
CONFIRMATION DRIVING PATTERN
a. Connect the hand-held tester to the DLC3.
b. Switch the hand-held tester from the "normal mode" to "check mode".
c. Start the engine and let the engine idle for 100 seconds or more.
d. Drive the vehicle at 40 km/h (25 mph) or more for 20 seconds or more.
e. Let the engine idle for 20 seconds or more.
f. Let the engine idle for 30 seconds.
HINT: If a malfunction exists, the MIL will light up during step (f).
NOTE:
If the conditions in this test are not strictly followed, detection of the malfunction will be impossible.
If you do not have the hand-held tester, turn the ignition switch OFF after performing steps (c) to (f), then perform steps (c) to (f) again.
CHECK FOR INTERMITTENT PROBLEMS
Hand-held tester only:
By putting the vehicle's ECM in the check mode, the 1 trip detection logic is possible instead of the 2 trip detection logic and the sensitivity to detect open circuits is increased. This makes it easier to detect intermittent problems.
1. Clear the DTCs.
2. Set the check mode.
3. Perform a simulation test.
4. Check the connector and terminal.
5. Handle the connector.