Troubleshooting
CIRCUIT DESCRIPTIONDTC Detecting Condition:
Fuel trim refers to the feedback compensation value compared against 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 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 over time 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 the DTC P0171 is recorded, the actual air-fuel ratio is on the LEAN side. When DTC P0172 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 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 + 38 %, the system is functioning normally.
- The oxygen sensor output voltage and the short-term fuel trim value can be read using the OBD II scan tool or TOYOTA hand-held tester.
CONFIRMATION DRIVING PATTERN
1. Connect the TOYOTA hand-held tester to the DLC3.
2. Switch the TOYOTA hand-held tester from normal mode to check mode.
3. Start the engine and let the engine idle for 100 sec. or more.
4. Drive the vehicle at 40 km/h (24 mph) or more for 20 Sec. or more.
5. Let the engine idle for 20 sec. or more.
6. Let the engine idle for 30 Sec.
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 TOYOTA hand-held tester, turn the ignition switch OFF after performing steps (3) to (6), then perform steps (3) to (6) again.
Steps 1 - 3:
Steps 5 - 7:
Steps 8 - 11:
INSPECTION PROCEDURE
HINT: Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool. Because freeze frame 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 warmed up or not, the air-fuel ratio lean or rich, etc. at the time of the malfunction.
CHECK FOR INTERMITTENT PROBLEMS
HINT:
TOYOTA 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 DTC.
b. Set the check mode.
c. Perform a simulation test.
d. Check the connector and terminal.
e. Handle the connector.