P0172
3UZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0171: System Too Lean (Bank 1)
DTC P0171 - System Too Lean (Bank 1)
DTC P0172 - System Too Rich (Bank 1)
DTC P0174 - System Too Lean (Bank 2)
DTC P0175 - System Too Rich (Bank 2)
DESCRIPTION
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 the stoichiometric air-fuel ratio. The signal from the heated oxygen sensor 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, the ECM determines this as a malfunction, illuminates the MIL and sets a DTC.
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 is then illuminated.
- If the total of the short-term fuel trim value and long-term fuel trim value is within the malfunction threshold (and ECT is more than 75°C (167°F)), the system is functioning normally.
MONITOR DESCRIPTION
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. Long-term fuel trim value is adjusted when persistent deviations in the short-term fuel trim's value are present. Also, the smoothed fuel trim learning value is adjusted when deviations from the ECM's simulated fuel injection value are present. The smoothed fuel trim learning value is a 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 malfunction threshold, the ECM interprets this as a fault in the fuel system and sets a DTC.
Example:
The smoothed fuel trim learning value is above 35% or below -35%. The ECM interprets this as a fault in the fuel system.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
TYPICAL MALFUNCTION THRESHOLDS
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT: It is possible that the malfunctioning area can be found using the Active Test Control the Injection Volume for A/F Sensor operation. The Active Test can determine if the heated oxygen sensor or other potential trouble areas are malfunctioning or not.
The injection volume can be switched to -12.5% (decrease) or +25% (increase) by the Active Test.
The Active Test procedure enables a technician to check and graph the output voltage of the heated oxygen sensors.
- Procedure:
1 Connect the Techstream to the DLC3.
2 Turn the ignition switch ON.
3 Warm up the engine by running the engine at 2500 rpm for approximately 90 seconds.
4 Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
5 Perform the Active Test while the engine is idling.
Standard:
The heated oxygen sensor reacts in accordance with the 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 heated oxygen sensor (sensor 1) output has a few seconds of delay and the heated oxygen sensor (sensor 2) output has a maximum of 20 seconds of delay.
If the vehicle is short on fuel, the air-fuel ratio becomes lean and the DTCs will be recorded.
HINT:
- Read freeze frame data using the Techstream. 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.
- A high heated oxygen sensor (sensor 1) voltage (0.55 V or more) indicates a rich air-fuel ratio.
- A low heated oxygen sensor (sensor 1) voltage (0.4 V or less) indicates a lean air-fuel ratio.
PROCEDURE
1. CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174, P0175)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON and turn the tester ON.
(c) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(d) Read the DTCs.
Result:
B -- GO TO RELEVANT DTC CHART
A -- Continue to next step.
2. CHECK CONNECTION OF PCV HOSE
OK:
PCV hose is connected correctly and is not damaged.
NG -- REPAIR OR REPLACE PCV HOSE
OK -- Continue to next step.
3. CHECK AIR INDUCTION SYSTEM
(a) Check the air induction system for vacuum leaks.
NG -- REPAIR OR REPLACE AIR INDUCTION SYSTEM
OK -- Continue to next step.
4. PERFORM ACTIVE TEST USING TECHSTREAM (A/F CONTROL)
(a) Perform the Active Test Control the Injection Volume for A/F Sensor with the Techstream and check the heated oxygen sensor status.
Standard voltage:
Heated oxygen sensor reacts in accordance with the increase and decrease of injection volume:
+25% -> Rich output: More than 0.55 V
-12.5% -> Lean output: Less than 0.4 V
HINT: L: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor almost always indicates 0.4 V or less (lean).
R: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor almost always indicates 0.5 V or more (rich).
D -- INSPECT HEATED OXYGEN SENSOR
C -- INSPECT FUEL INJECTOR
B -- CHECK FOR EXHAUST GAS LEAKAGE
A -- Continue to next step.
5. READ VALUE USING TECHSTREAM (COOLANT TEMP)
(a) Connect the Techstream to the DLC3.
(b) Enter the following menus: Powertrain / Engine and ECT / Data List / Coolant Temp.
(c) Read the Coolant Temp value when the engine is cold and warmed up.
Standard:
ECT when the engine is cold: Same as ambient temperature
ECT when the engine is warmed up: 75 to 95°C (167 to 203°F)
NG -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR
OK -- Continue to next step.
6. READ VALUE USING TECHSTREAM (MAF)
(a) Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.
(b) Allow the engine to idle until the ECT reaches 75°C (167°F).
(c) Read the MAF value at idle rpm.
Standard:
MAF at idle rpm: 4.6 to 5.6 g/sec. (shift lever is in N position and A/C is OFF)
NG -- REPLACE MASS AIR FLOW METER
OK -- Continue to next step.
7. CHECK FUEL PRESSURE
(a) Check the fuel pressure Testing and Inspection.
NG -- REPAIR OR REPLACE FUEL SYSTEM
OK -- Continue to next step.
8. CHECK FOR EXHAUST GAS LEAKAGE
NG -- REPAIR OR REPLACE EXHAUST SYSTEM
OK -- Continue to next step.
9. CHECK FOR SPARK AND IGNITION
HINT: If the spark plugs or ignition system malfunction, engine misfire may occur. The misfire counter can be read with the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Misfire / Cylinder #1 Misfire Count to #8.
NG -- REPAIR OR REPLACE IGNITION SYSTEM
OK -- Continue to next step.
10. INSPECT FUEL INJECTOR
HINT: If the injectors are malfunctioning, engine misfire may occur. The misfire counter can be read with the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Misfire / Cylinder #1 Misfire Count to #8.
NG -- REPLACE FUEL INJECTOR
OK -- Continue to next step.
11. INSPECT HEATED OXYGEN SENSOR
(a) Disconnect the H9 and H10 sensor connectors.
(b) Measure the resistance of the heated oxygen sensor.
Standard resistance:
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
12. INSPECT EFI RELAY (Marking: EFI)
(a) Remove the EFI relay from the engine room No. 2 relay block.
(b) Measure the resistance of the EFI relay.
Standard resistance:
NG -- REPLACE EFI RELAY
OK -- Continue to next step.
13. CHECK WIRE HARNESS (HEATED OXYGEN SENSOR (SENSOR 1) - ECM)
(a) Disconnect the H9 and H10 sensor connectors.
(b) Disconnect the E2 and E4 ECM connectors.
(c) Measure the resistance of the wire harness side connectors.
Standard resistance:
NG -- REPAIR OR REPLACE HARNESS AND CONNECTOR
OK -- Continue to next step.
14. REPLACE HEATED OXYGEN SENSOR
NEXT -- Continue to next step.
15. PERFORM CONFIRMATION DRIVING PATTERN
- (a) Connect the Techstream to the DLC3.
- (b) Switch the tester from normal mode to check mode Check Mode Procedure.
- (c) Allow the engine to idle until the ECT reaches 75°C (167°F).
- (d) Allow the vehicle to run at 40 km/h (25 mph) or more for 25 seconds or more.
- (e) Allow the engine to idle for 30 seconds or more.
- (f) Perform steps (d) and (e) at least 3 times.
HINT: If a malfunction exists, the MIL will be illuminated on the multi-information display.
NOTE:
If the conditions in this test are not strictly followed, you should perform steps (d) and (e).
If you do not have the Techstream, turn the ignition switch OFF after performing steps (c) and (f), and then perform steps (c) and (f) again.
- (g) Allow the engine to idle for 30 seconds.
NEXT -- END