Troubleshooting

DTC P0175 SYSTEM TOO RICH (FUEL TRIM) (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 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.

Long-term fuel trim compensates the deviation from the central value of the short-term fuel trim stored 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 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 long-term fuel trim value is within ±35 % (80 °C (176 °F) or more), the system the system is functioning normally.
- The A/F sensor (bank 1, 2 sensor 1) output voltage and the short-term fuel trim value can be read using the OBD II scan tool or LEXUS hand-held tester.
- The ECM controls the voltage of the AFR+, AFL+, AFR- and AFL- terminals of the ECM to the fixed voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without OBD II scan tool or LEXUS hand-held tester.
- OBD II scan tool (excluding LEXUS hand-held tester) displays the one fifth of the A/F sensor output voltage which is displayed on the LEXUS hand-held tester.

Wiring Diagram:

Step 1 - 2:

Step 3 - 7:

Step 8:

Step 9 - 12:

INSPECTION PROCEDURE

CHECK FOR INTERMITTENT PROBLEMS

LEXUS hand-held tester only:
By putting the vehicle's ECM in the 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.
1. Clear the DTC.
2. Set the check mode.
3. Perform a simulation test.
4. Check the connector and terminal.
5. Handle the connector.

Confirmation Driving Pattern:

CONFIRMATION DRIVING PATTERN
1. Connect the LEXUS hand-held tester to the DLC3.
2. Switch the LEXUS hand-held tester from the normal mode to the check mode.
3. Start the engine and warm it up with all the accessory switches OFF.
4. Drive the vehicle at 60 - 120 km/h (38 - 75 mph) and engine speed at 1,400 - 3,200 rpm for 3 - 5 minutes.

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

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 (c) and (d), then perform steps (c) and (d) again.