Troubleshooting
DTC P0172 SYSTEM TOO RICH (FUEL TRIM) (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 Heated Oxygen Sensor (HO2S) indicates whether the air-fuel ratio is RICH or LEAN compared to the stoichiometric air-fuel ratio. This variance triggers 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 short-term fuel trim varies from the central value due to individual engine differences, wear over time and changes in the operating environment. The long-term fuel trim, which controls overall fuel compensation, steadies long-term deviations of the short-term fuel trim from the central value.
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, the Malfunction Indicator Light (MIL) is illuminated and a DTC is set.
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 may be recorded.The MIL then turns on.
- If the total of the short-term fuel trim value and long-term fuel trim value is within the malfunction threshold (ECT is more than 75 °C (167 °F)), 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 a simulated fuel injection amount by the ECM affects the smoothed fuel trim learning value. The smoothed fuel trim learning value which 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 leaning value is above 40% or below -35%. The ECM interprets this as a failure in the fuel system.
Step 1 - 2:
Step 3 - 4:
Step 5 - 9:
Step 10 - 12:
Step 13 - 14:
Step 15:
INSPECTION PROCEDURE
HINT: Narrowing down the trouble area is possible by performing the A/F CONTROL on the Active Test (HO2S or other trouble areas can be distinguished).
The injection volume can be switched to -12.5 % (decrease) or +25 % (increase) by A/F Control.
The A/F CONTROL procedure enables a technician to check and graph the voltage outputs of the HO2Ss.
A/F Control Procedure:
a. Connect the hand-held tester to the DLC3 on the vehicle.
b. Turn the ignition switch ON.
c. Warm up the engine by running the engine at 2,500 rpm for approximately 90 seconds.
d. Select the item "DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL".
e. Perform A/F CONTROL at the engine idling.
Standard:
The HO2S 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: The front HO2S output has a few seconds of delay and the rear HO2S output has a maximum of 20 seconds of delay.
If the vehicle is short of fuel, the air-fuel ratio becomes LEAN and the DTCs will be recorded.
HINT: Read freeze frame data using the hand-held tester. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.