Troubleshooting
DTC P0171 SYSTEM TOO LEAN (FUEL TRIM) (BANK 1)DTC P0172 SYSTEM TOO RICH (FUEL TRIM) (BANK 1)
DTC P0174 SYSTEM TOO LEAN (FUEL TRIM) (BANK 2)
DTC P0175 SYSTEM TOO RICH (FUEL TRIM) (BANK 2)
CIRCUIT DESCRIPTION
DTC Detecting condition:
Fuel trim is related to the feedback compensation value, not 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 are LEAN or RICH beyond exceed 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 lights up.
- 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 by using the OBD II scan tool or LEXUS hand-held tester.
- The ECM controls the voltage of the AF+ and AF- 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:
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, the detection of the malfunction is impossible.
If you do not have a LEXUS hand-held tester, turn the ignition switch OFF after performing steps (c) and (d) once, then perform steps (c) and (d) again.
Steps 1 - 3:
Steps 4 - 7:
Step 7 (continued) - 10:
Step 11:
INSPECTION PROCEDURE
HINT: Read freeze frame data using LEXUS hand-held tester or OBD II scan tool, as freeze frame data records the engine conditions when the 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.
CHECK FOR INTERMITTENT PROBLEMS
HINT:
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 the sensitivity to detect open circuits is increased. This makes it easier to detect intermittent problems.
a. Clear the DTC (See step 2).
b. Set the check mode (See step 3).
c. Perform a simulation test.
d. Check the connector and terminal.
e. Handle the connector.