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 A/F sensor is approximately proportional to the existing air-fuel ratio, and ECM compares 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 for the deviation from the central value of the short-term fuel trim stored by each engine tolerance, and the deviation from the central value due to the passage of time and changes of 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 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 ± 35% (80 °C (176 °F) or more), the system is functioning normally.
- The A/F sensor (bank 1 sensor 1) output voltage and the short-term fuel trim value can be read using the hand-held tester or OBD II scan tool.
- The ECM controls the voltage of the terminals AF1 + and AF1- of the ECM to the fixed voltage. Therefore it is impossible to confirm the A/F sensor output voltage without hand-held tester or OBD II scan tool.
- OBD II scan tool (excluding hand-held tester) displays the one fifth of the A/F sensor (bank 1 sensor 1) output voltage which is displayed on the hand-held tester.

Wiring Diagram:

CONFIRMATION DRIVING PATTERN

Confirmation Driving Pattern:

a. Connect the hand-held tester to the DLC3.
b. Switch the hand-held tester from the normal mode to the check mode.
c. Start the engine and warm it up with all the accessory switched OFF.
d. Drive the vehicle at 60 - 120 km/h (38 - 75 mph) and the engine speed at 1,600 - 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 impossible.
- Without a hand-held tester, turn the ignition switch OFF after performing steps (c) and (d), then perform steps (c) and (d) again.

Step 1 - 4:

Step 4(continued) - 8:

Step 8(continued) - 11:

Step 11(continued) - 12:

INSPECTION PROCEDURE

HINT: Read freeze frame data using 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 warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.

CHECK FOR INTERMITTENT PROBLEMS

HINT:
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 DTCs.
b. Set the check mode.
c. Perform a simulation test.
d. Check the connector and terminal.
e. Handle the connector.