Troubleshooting
DTC P0172 SYSTEM TOO RICH (BANK 1)CIRCUIT DESCRIPTION
DTC Detecting Condition:
The Fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim includes the short-term fuel trim and long-term fuel trim.
The 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 air fuel ratio sensor is approximately proportional to the existing air-fuel ratio. 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.
The long-term fuel trim compensates for 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 environment.
If both the short-term fuel trim and the long-term fuel trim 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 comes on.
- If the total of the short-term fuel trim value and the long-term fuel trim value is within ±35% (75 °C or more), the system is functioning normally.
- The air fuel ratio sensors (bank 1, 2 sensor 1) output voltage and the short-term fuel trim value can be read using the OBD II scan tool or the hand-held tester.
- The ECM controls the voltage of AFR+, AFL+, AFR- and AFL- terminals of ECM to the fixed voltage. Therefore, it is impossible to confirm the air fuel ratio sensor output voltage without OBD II scan tool or hand-held tester.
- OBD II scan tool (excluding hand-held tester) displays the one fifth of the air fuel ratio sensors (bank 1, 2 sensor 1) output voltage which is displayed on the hand-held tester.
Wiring Diagram:
Step 1 - 5:
Step 6 - 8:
Step 9:
Step 9 (continued) - 11:
Step 12 - 13:
Step 14 - 18:
Step 19:
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
The narrowing down the trouble area is possible by performing ACTIVE TEST of the following "A/F CONTROL" (oxygen sensor or another can be distinguished).
a. Perform ACTIVE TEST by hand-held tester (A/F CONTROL).
HINT: "A/F CONTROL" is an ACTIVE TEST which changes the injection volume to -12.5 % or +25 %.
1. Connect the hand-held tester to the DLC3 on the vehicle.
2. Turn the ignition switch ON.
3. Warm up the engine with the engine speed at 2,500 rpm for approx. 90 sec.
4. Select the item "DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/A/F CONTROL".
5. Perform "A/F CONTROL" when idle condition (press the right or left button).
Result: Air fuel ratio sensor and oxygen sensor reacts in synchronizing with increase and decrease of injection volume (+25 % rich output: 1 V, -12.5 % lean output: 0 V)
NOTE: However, there is a few second delay in the sensor 1 (front air fuel ratio sensor) output. And there is about 20 seconds delay in the sensor 2 (rear oxygen sensor).
The following procedure of A/F CONTROL enable that to check its output (show its graph indication) of air fuel ratio sensor and oxygen sensor.
To display the graph indication. Select and push the "YES or NO" button 2 data "AFS B1 S1 and O2S B1 S2" or "AFS B2S1 and O2S B2S2" and press button "4" after selecting "ACTIVE TEST/ A/F CONTROL/USER DATA".
HINT: Read freeze frame data using the hand-held tester or the 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
Hand-held tester only:
By putting the vehicle's ECM in the check mode, the 1 trip detection logic is possible instead of 2 trip detection logic and sensitivity the 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.
CONFIRMATION DRIVING PATTERN
1. Connect the hand-held tester to the DLC3. (*1)
2. Switch the hand-held tester 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 (25 mph) or more for 40 seconds or more. (*3)
5. Let the engine idle for 10 seconds or more. (*4)
6. Perform steps (*3) to (*4) 12 times. (*5)
HINT: If a malfunction exists, the MIL will light up on the multi information display during step. (*5)
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 hand-held tester, turn the ignition switch OFF after performing steps from (*2) to (*5), then perform steps from (*2) to (*5) again.