Troubleshooting

DTC P0174 SYSTEM TOO LEAN (A/F LEAN MALFUNCTION, BANK 2)

CIRCUIT DESCRIPTION

DTC Detecting Condition:

Fuel trim refers to the feedback compensation value compared to the basic injection time. Fuel trim includes short-term fuel trim and long-term fuel trim.

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 fuel volume if the air-fuel ratio is rich, and an increase in fuel volume if it is lean.

Long-term fuel trim is overall fuel compensation carried out long-term to compensate for continual deviation of the short-term fuel trim from the central value due to individual engine differences, wear overtime and changes in the usage environment.

If both the short-term fuel trim and 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 %, the system is functioning normally.

Wiring Diagram:

Step 1:

Step 2 - 6:

Step 7 - 9:

Step 10 - 11:

INSPECTION PROCEDURE

Confirmation Driving Pattern:

CONFIRMATION DRIVING PATTERN
1. Connect the LEXUS hand-held tester to the DLC3.
2. Switch the LEXUS hand-held tester from normal mode to check mode.
3. Start the engine and let the engine idle for 120 seconds or more
4. Drive the vehicle at 40 km/h (24 mph) or more for 20 seconds or more.
5. Let the engine idle for 20 Seconds or more.
6. Let the engine idle for 20 Seconds.

HINT: If a malfunction exists, the MIL will light up during step (6).

NOTE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
If you do not have a LEXUS hand-held tester, turn the ignition switch OFF after performing steps (3) to (6), then perform steps (3) to (6) again.

CHECK FOR INTERMITTENT PROBLEMS

HINT:
LEXUS hand-held tester only:
By putting the vehicle's ECM in check mode, 1 trip detection logic is possible instead of 2 trip detection logic and sensitivity to detect open circuits is increased. This makes it easier to detect intermittent problems.

a. Clear the DTCs.
b. Set the check mode.
c. Perform a simulation test.
d. Check the connector and terminal.
e. Handle the connector.