Troubleshooting

DTC P0172 SYSTEM TOO RICH (FUEL TRIM) (BANK 1)

CIRCUIT DESCRIPTION

DTC Detecting Condition:

Fuel trim refers to the feedback compensation value compared against the basic inspection 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 form 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 check engine warning (CHK ENG) lights up.

HINT: 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 - 7:

Step 8 - 9:

Step 9 (Continued) - 12:

INSPECTION PROCEDURE

HINT: Read freed frame data using 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.

CONFIRMATION DRIVING PATTERN

Confirmation Driving Pattern:

1. Connect the hand-held tester or OBD II scan tool to the DLC3.
2. Switch the hand-held tester or OBD II scan tool from the normal mode to the check (test) mode. (*1)
3. Start the engine and let the engine idle for 60 seconds or more. (*2)
4. Drive the vehicle at 40 km/h (24 mph) or more for 40 seconds or more. (*3)
5. Let the engine idle for 10 seconds or more. (*4)
6. Preform steps (*3) to (*4)11 times. (*5)

HINT: If a malfunction exists, the MIL will light up on the multi information display during step (*5).

NOTE: It the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
If you do not have a hand-held tester, turn the ignition switch OFF after performing steps from (*2) to (*5), then perform steps from (*2) to (*5) again.

CHECK FOR INTERMITTENT PROBLEMS

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.

1. Clear the DTC.
2. Set the check mode .
3. Perform a simulation test.
4. Check the connector and terminal.
5. Handle the connector.