SFI SYSTEM (w/ Secondary Air Injection System), Diagnostic DTC:P0171, P0172
| DTC Code | DTC Name |
|---|---|
| P0171 | System Too Lean (Fuel Trim) |
| P0172 | System Too Rich (Fuel Trim) |
DESCRIPTION
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim consists of both the short-term and long-term fuel trims.
The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at stoichiometric levels. The signal from the Air-Fuel Ratio (A/F) sensor indicates whether the air-fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel ratio is rich and an increase in the fuel injection volume if it is lean.
Factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-term fuel trim compensation.
If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.
| DTC No. | DTC Detection Conditions | Trouble Areas |
|---|---|---|
| P0171 | With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to lean side (2 trip detection logic) |
|
| P0172 | With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to rich side (2 trip detection logic) |
|
Tech Tips
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When DTC P0171 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 is set, the actual air-fuel ratio is on the rich side.
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If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 may be set. The MIL is then illuminated.
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When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and the engine coolant temperature is more than 75°C [167°F]), the system is functioning normally.
MONITOR DESCRIPTION
Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the ECM's estimated fuel injection volumes also affect the average fuel trim learning value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learning value of the air-fuel ratio). If the average fuel trim learning value exceeds the malfunction thresholds, the ECM interprets this a fault in the fuel system and sets a DTC.
Example:
The average fuel trim learning value is more than +35 % or less than -35 %, the ECM interprets this as a fuel system malfunction.
WIRING DIAGRAM
Refer to DTC P2195 Click here.
INSPECTION PROCEDURE
Tech Tips
Intelligent tester only:
Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor function can help to determine whether the Air-Fuel Ratio (A/F) sensor, Heated Oxygen (HO2) sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the Control the Injection Volume for A/F Sensor operation using an intelligent tester.
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Connect an intelligent tester to the DLC3.
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Start the engine and turn the tester ON.
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Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
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On the tester, select the following menu items: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
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Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition.
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Monitor the voltage outputs of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.
Tech Tips
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The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5 % or increases the injection volume by 25 %.
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Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
| Voltage | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Note
The Air-Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2) sensor has a maximum output delay of approximately 20 seconds.
| Case | A/F Sensor (Sensor 1) Output Voltage |
HO2 Sensor (Sensor 2) Output Voltage |
Mainly Suspected Trouble Areas |
||
|---|---|---|---|---|---|
| 1 | Injection volume +25 % -12.5 % |
 |
Injection volume +25 % -12.5 % |
|
- |
| Output voltage More than 3.4 V Less than 3.1 V |
 |
Output voltage More than 0.5 V Less than 0.4 V |
 |
||
| 2 | Injection volume +25 % -12.5 % |
|
Injection volume +25 % -12.5 % |
|
|
| Output voltage Almost no reaction |
 |
Output voltage More than 0.5 V Less than 0.4 V |
|
||
| 3 | Injection volume +25 % -12.5 % |
|
Injection volume +25 % -12.5 % |
|
|
| Output voltage More than 3.4 V Less than 3.1 V |
|
Output voltage Almost no reaction |
|
||
| 4 | Injection volume +25 % -12.5 % |
|
Injection volume +25 % -12.5 % |
|
(Air-fuel ratio extremely lean or rich) |
| Output voltage Almost no reaction |
|
Output voltage Almost no reaction |
|
||
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Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.
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To display the graph, select the following menu items on the tester: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / User Data / AFS Voltage B1S1 and O2S B1S2.
Tech Tips
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Read freeze frame data using an intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air-fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
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A low A/F sensor voltage could be caused by a rich air-fuel mixture. Check for conditions that would cause the engine to run rich.
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A high A/F sensor voltage could be caused by a lean air-fuel mixture. Check for conditions that would cause the engine to run lean.
PROCEDURE
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CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 AND P0172)
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Connect an intelligent tester to the DLC3.
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Turn the ignition switch to the ON position and turn the tester ON.
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Select the following menu items: Powertrain / Engine and ECT / DTC.
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Read DTCs.
Result Display (DTC Output) Proceed To P0171 or P0172 A P0171 or P0172 and other DTCs B Tech Tips
If any DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.
B 
GO TO DTC CHART
A 
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-
CHECK PCV HOSE
OK PCV hose is connected correctly and is not damaged.
NG
REPAIR OR REPLACE PCV HOSE
OK
-
CHECK AIR INDUCTION SYSTEM
-
Check the air induction system for vacuum leakage.
OK No leakage from air induction system.
NG
CHECK AIR INDUCTION SYSTEM
OK
-
-
PERFORM ACTIVE TEST USING INTELLIGENT TESTER (A/F CONTROL)
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Connect the intelligent tester to the DLC3.
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Start the engine and turn the tester ON.
-
Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
-
On the tester, select the following menu items: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
-
Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition.
-
Monitor the voltage outputs of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.
Tech Tips
-
The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5 % or increases the injection volume by 25 %.
-
Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
Voltage Tester Display
(Sensor)
Injection Volumes Status Voltages AFS Voltage B1S1
(A/F)
+25 % Rich Less than 3.1 AFS Voltage B1S1
(A/F)
-12.5 % Lean More than 3.4 O2S B1S2
(HO2)
+25 % Rich More than 0.5 O2S B1S2
(HO2)
-12.5 % Lean Less than 0.4 Result Status
AFS Voltage B1S1
Status
O2S B1S2
A/F Condition and
A/F Sensor Condition
Misfires Suspected Trouble Areas Proceed To Lean/Rich Lean/Rich Normal - - C Lean Lean Actual air-fuel ratio lean May occur
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PCV valve and hose
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PCV hose connections
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Injector blockage
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Gas leakage from exhaust system
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Air induction system
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Fuel pressure
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Mass Air Flow (MAF) meter
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Engine Coolant Temperature (ECT) sensor
A Rich Rich Actual air-fuel ratio rich -
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Injector leakage or blockage
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Gas leakage from exhaust system
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Ignition system
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Fuel pressure
-
MAF meter
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ECT sensor
A Lean Lean/Rich A/F sensor malfunction -
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A/F sensor
B Rich Lean/Rich A/F sensor malfunction -
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A/F sensor
B Lean: During Control the Injection Volume for A/F Sensor, the A/F sensor output voltage (AFS) is consistently more than 3.35 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.
Rich: During Control the Injection Volume for A/F Sensor, the AFS is consistently less than 3.0 V, and the O2S is consistently more than 0.5 V.
Lean/Rich: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor alternates correctly.
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B 
INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here
C
PERFORM CONFIRMATION DRIVING PATTERN Click here
A
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READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)
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Connect the intelligent tester to the DLC3.
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Turn the ignition switch to the ON position and turn the tester ON.
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Select the following menu items: Powertrain / Engine and ECT / Data List / Coolant Temp.
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Read the Coolant Temp twice, when the engine is both cold and warmed up.
Standard With cold engine Same as ambient air temperature. With warm engine Between 75°C and 95°C (167°F and 203°F)
NG
REPLACE ENGINE COOLANT TEMPERATURE SENSOR
OK
-
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READ VALUE USING INTELLIGENT TESTER (MAF)
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Connect the intelligent tester to the DLC3.
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Turn the ignition switch to the ON position and turn the tester ON.
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Select the following menu items: Powertrain / Engine and ECT / Data List / MAF and Coolant Temp.
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Allow the engine to idle until the Coolant Temp reaches 75°C (167°F) or more.
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Read the MAF with the engine in an idling condition and at an engine speed of 2,500 rpm.
Standard MAF while engine idling Between 2.0 g/s and 4.5 g/s (shift position: N, A/C: OFF). MAF at engine speed of 2,500 rpm Between 8.0 g/s and 14.7 g/s (shift position: N, A/C: OFF).
NG
REPLACE MASS AIR FLOW METER
OK
-
-
CHECK FUEL PRESSURE
-
Check the fuel pressure.
NG
REPAIR OR REPLACE FUEL SYSTEM
OK
-
-
CHECK FOR EXHAUST GAS LEAKAGE
OK No gas leakage.
NG
REPAIR OR REPLACE EXHAUST SYSTEM
OK
-
CHECK SPARK AND IGNITION
Tech Tips
If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using an intelligent tester. Select the following menu items: Powertrain / Engine and ECT / Data List / Cylinder # Misfire Count (CYL #1 to CYL #4).
NG
REPAIR OR REPLACE IGNITION SYSTEM
OK
-
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
Tech Tips
If the injectors malfunction, engine misfire may occur. The misfire count can be read using an intelligent tester. Select the following menu items: Powertrain / Engine and ECT / Data List / Cylinder # Misfire Count (CYL #1 to CYL #4).
NG
REPLACE FUEL INJECTOR ASSEMBLY
OK
-
INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
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Disconnect the D33 A/F sensor connector.
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Measure the resistance between the terminals of the A/F sensor connector.
Resistance Tester Connections Specified Conditions HA1A (1) - +B (2) 1.8 to 3.4 Ω at 20°C (68°F) HA1A (1) - A1A- (4) 10 kΩ or higher -
Reconnect the A/F sensor connector.
NG
REPLACE AIR FUEL RATIO SENSOR
OK
-
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INSPECT INTEGRATION NO.1 RELAY (A/F HEATER RELAY)
-
Remove the integration relay from the engine room R/B No.1.
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Measure the integration relay (A/F HEATER relay) resistance.
Resistance Tester Connections Specified Conditions A1 - C4 10 kΩ or higher A1 - C4 Below 1 Ω
(when battery voltage applied to terminals C2 and C3)
-
Reinstall the integration relay.
NG
REPLACE INTEGRATION NO.1 RELAY
OK
-
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CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)
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Disconnect the D33 A/F sensor connector.
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Turn the ignition switch to the ON position.
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Measure the voltage between the +B terminal of the A/F sensor connector and body ground.
Voltage Tester Connections Specified Conditions +B (D33-2) - Body ground 9 to 14 V -
Turn the ignition switch to OFF.
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Disconnect the D1 ECM connector.
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Measure the resistance.
Resistance (Check for open) Tester Connections Specified Conditions HA1A (D33-1) - HA1A (D1-1) Below 1 Ω A1A+ (D33-3) - A1A+ (D1-21) Below 1 Ω A1A- (D33-4) - A1A- (D1-31) Below 1 Ω Resistance (Check for short) Tester Connections Specified Conditions HA1A (D33-1) or HA1A (D1-1) - Body ground 10 kΩ or higher A1A+ (D33-3) or A1A+ (D1-21) - Body ground 10 kΩ or higher A1A- (D33-4) or A1A- (D1-31) - Body ground 10 kΩ or higher -
Reconnect the ECM connector.
-
Reconnect the A/F sensor connector.
NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK
-
-
REPLACE AIR FUEL RATIO SENSOR
NEXT
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PERFORM CONFIRMATION DRIVING PATTERN
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Connect the intelligent tester to the DLC3.
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Turn the ignition switch to the ON position and turn the tester ON.
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Clear DTCs Click here.
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Switch the ECM from normal mode to check mode using the tester Click here.
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Start the engine and warm it up with all the accessories switched OFF.
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Drive the vehicle at between 60 km/h and 120 km/h (38 mph and 75 mph) and at an engine speed of between 1,400 rpm and 3,200 rpm for 3 to 5 minutes.
Tech Tips
If the system is still malfunctioning, the MIL will be illuminated during step (f).
Note
If the conditions in this test are not strictly followed, no malfunction will be detected.
NEXT
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CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)
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On the intelligent tester, select the following menu items: Powertrain / Engine and ECT / DTC.
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Read DTCs.
Result Display (DTC Output) Proceed To No output A P0171 or P0172 B
B
READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP) Click here
A 
END
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