Troubleshooting

P0172 - System Too Rich (Fuel Trim)
CIRCUIT DESCRIPTION

DTC Detection 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 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.

Long-term fuel trim is 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 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 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 ±25 %, the system functions normally.

Wiring Diagram:

CONFIRMATION DRIVING PATTERN

Confirmation Driving Pattern:

1. Connect the hand-held tester to the DLC3.
2. Switch the hand-held tester from the normal mode to the check (test) mode.
3. Start the engine and let the engine idle for 100 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 30 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 be impossible.
If you do not have a TOYOTA hand-held tester, turn the ignition switch OFF after performing steps (3) to (6) once, then perform steps (3) to (6) again.

Steps 1 - 5:

Steps 6 - 8:

Steps 9 - 11:

INSPECTION PROCEDURE

HINT: Read freeze frame data using TOYOTA hand-held tester or 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.

CHECK FOR INTERMITTENT PROBLEMS

TOYOTA 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 DTCs.
2. Set the check mode.
3. Perform a simulation test.
4. Check the connector and terminal.
5. Handle the connector.