P0172
DTC P0172 SYSTEM TOO RICH (BANK 1)CIRCUIT DESCRIPTION
DTC Detection 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 the long-term fuel trim.
The short-term fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at stoichiometric air-fuel ratio. The signal from the A/F sensor indicates whether the air-fuel ratio is RICH or LEAN compared to the stoichiometric air-fuel ratio, triggering a reduction in the fuel volume if the air-fuel ratio is RICH, and an increase in the fuel volume if it is LEAN.
The long-term fuel trim is the 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 over time and changes in the using environment.
If both the short-term fuel trim and the long-term fuel trim are LEAN or RICH beyond a certain value, it is detected as a malfunction and the MIL is illuminated.
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 long-term fuel trim value is within (+) 35% (75°C), the system is functioning normally.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
Under closed-loop fuel control, fuel injection amounts that deviate from the ECM's estimated fuel amount will cause a change in the long-term fuel trim compensation value. This long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. And the deviation from the simulated fuel injection amount by the ECM affects a smoothed fuel trim learning value. The smoothed fuel trim learning value is the combination of smoothed short-term fuel trim (fuel feedback compensation value) and smoothed long-term fuel trim (learning value of the air-fuel ratio). When the smoothed fuel trim learning value exceeds the DTC threshold, the ECM interprets this as a fault in the fuel system and sets a DTC.
Example:
The smoothed fuel trim learning value is more than +35% or less than -35%. The ECM interprets this as a failure in the fuel system.
Wiring Diagram:
Step 1 - 4:
Step 5 - 8:
Step 9:
Step 9(Continued) - 11:
Step 12 - 13:
Step 14 - 18:
Step 19 - 22:
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
Narrowing down the trouble area is possible by performing ACTIVE TEST of the following "A/F CONTROL" (A/F sensor, heated oxygen sensor or other trouble areas can be distinguished).
a. Perform ACTIVE TEST by the hand-held tester (A/F CONTROL).
HINT: "A/F CONTROL" is 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:
A/F sensor reacts in accordance with increase and decrease of injection volume:
+25% -> rich output: Less than 3.0 V
-12.5% -> lean output: More than 3.35 V
Heated oxygen sensor reacts in accordance with increase and decrease of injection volume:
+25% -> rich output: More than 0.55 V
-12.5% -> lean output: Less than 0.4 V
NOTE: There is a few second delay in the A/F sensor output and there is about 20 seconds delay in the heated oxygen sensor output.
The following procedure of A/F CONTROL enables the user to check its output (show its graph indication)of A/F sensor and heated oxygen sensor.
For displaying the graph indication, enter "ACTIVE TEST/ A/F CONTROL/USER DATA", then select "AFS B1S1 and O2S B1S2" or "AFS B2S1 and O2S B2S2" by pressing "YES" button and push "ENTER" button before pressing "F4" button.
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.
- A high A/F sensor voltage could be caused by a rich air fuel mixture. Check the conditions that would cause the engine to run rich.
- A low A/F sensor voltage could be caused by a lean air fuel mixture. Check the conditions that would cause the engine to run lean.
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 the 2 trip detection logic, and the sensitivity to detect faults 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. Wiggle the harness and the connector.