- Air induction system
- Injector blockage
- Mass Air Flow (MAF) meter
- Engine Coolant Temperature (ECT) sensor
- Fuel pressure
- Gas leak from exhaust system
- Open or short in A/F sensor (for sensor 1) circuit
- A/F sensor (for sensor 1)
- A/F sensor heater (for sensor 1)
- Integration relay
- A/F sensor heater and integration relay circuits
- PCV valve and hose
- PCV hose connections
- ECM
| Last Modified: 11-29-2007 | 1.6 C | |
| Service Category: Engine/Hybrid System | Section: Engine Control | |
| Model Year: 2008 | Model: Sequoia | Doc ID: RM000000WC305KX |
| Title: 2UZ-FE ENGINE CONTROL: SFI SYSTEM: DESCRIPTION (2008 Sequoia) | ||
|
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 consists of both the short-term and the 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 term 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.
|
DTC No. |
DTC Detection Condition |
Trouble Area |
|---|---|---|
|
P0171 P0174 |
With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to lean side (2 trip detection logic) |
|
|
P0172 P0175 |
With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to rich side (2 trip detection logic) |
|
HINT:
- When DTC P0171 or P0174 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 is stored, 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 set. The MIL is then illuminated.
- 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 threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.
Example:
The average fuel trim learning value is +35% or more or -35% or less, the ECM interprets this as a fuel system malfunction.
MONITOR STRATEGY
|
Related DTCs |
P0171: Fuel trim lean (bank 1) P0172: Fuel trim rich (bank 1) P0174: Fuel trim lean (bank 2) P0175: Fuel trim rich (bank 2) |
|
Required Sensors/Components (Main) |
Fuel system |
|
Required Sensors/Components (Related) |
A/F sensor, Mass air flow meter, Crankshaft position sensor |
|
Frequency of Operation |
Continuous |
|
Duration |
Within 10 seconds |
|
MIL Operation |
2 driving cycles |
|
Sequence of Operation |
None |
TYPICAL ENABLING CONDITIONS
|
Monitor runs whenever following DTCs not present |
P0010, P0020 (VVT OCV) P0011 (VVT System 1 - Advance) P0012 (VVT System 1 - Retard) P0021 (VVT System 2 - Advance) P0022 (VVT System 2 - Retard) P0031, P0032, P0051, P0052 (A/F Sensor Heater - Sensor 1) P0102 - P0103 (MAF meter) P0115 - P0118 (ECT sensor) P0120 - P0223, P2135 (TP sensor) P0125 (Insufficient ECT for Closed Loop) P0335 (CKP sensor) P0351 - P0354 (Igniter) P0500 (VSS) P2440 (AIR control valve stuck open) P2441 (AIR control valve stuck close) P2444 (AIP stuck On) P2445 (AIP stuck Off) |
|
Fuel system status |
Closed loop |
|
Battery voltage |
11 V or more |
|
Either of following conditions 1 or 2 set |
- |
|
1. Engine RPM |
Below 1000 rpm |
|
2. Intake air amount per revolution |
0.26 g/rev or more |
|
Catalyst monitor |
Not executed |
TYPICAL MALFUNCTION THRESHOLDS
|
Purge-cut |
Executing |
|
Either of following conditions 1 or 2 met |
- |
|
1. Average of short-term fuel trim and long-term fuel trim |
35% or more (varies with ECT) |
|
2. Average of short-term fuel trim and long-term fuel trim |
-35% or less (varies with ECT) |
WIRING DIAGRAM
Refer to DTC P2195
.
INSPECTION PROCEDURE
HINT:
- Read freeze frame data using the Techstream. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, 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 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.
- 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
|
1. |
CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175) |
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON.
(c) Turn the Techstream ON.
(d) Enter the following menus: Powertrain / Engine / Trouble Codes.
(e) Read DTCs.
Result
|
Result |
Proceed to |
|---|---|
|
P0171, P0172, P0174 or P0175 is output |
A |
|
P0171, P0172, P0174 or P0175 and other DTCs are output |
B |
HINT:
If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.
|
|
2. |
PERFORM ACTIVE TEST USING TECHSTREAM (A/F CONTROL) |
(a) Connect the Techstream to the DLC3.
(b) Start the engine.
(c) Turn the Techstream ON.
(d) Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
(e) Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.
(f) Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
(g) Monitor the output voltages of A/F and HO2 sensors (AFS B1S1 and O2S B1S2 or AFS B2S1 and O2S B2S2) displayed on the Techstream.
Standard:
The A/F sensor reacts in accordance with increases and decreases in the fuel injection volume:
+25% = Rich output:
Less than 3.0 V
-12.5% = Lean output:
More than 3.35 V
NOTICE:
The A/F sensor has an output delay of a few seconds and the 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 |
Main Suspected Trouble Area |
|---|---|---|---|
|
1 |
|
|
- |
|
2 |
|
|
|
|
3 |
|
|
|
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.
To display the graph on the Techstream, enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/ F Sensor / A/F Control System / AFS B1 S1 and O2S B1 S2 or AFS B2 S1 and O2S B2 S2, then press the graph button on the Data List view.
Result
|
Result |
Proceed to |
|---|---|
|
Case 1 |
C |
|
Case 2 |
B |
|
Case 3 |
A |
|
|
3. |
READ VALUE USING TECHSTREAM (MAF) |
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON.
(c) Turn the Techstream ON.
(d) Enter the following menus: Powertrain / Engine / Data List / All Data / MAF and Coolant Temp.
(e) Allow the engine to idle until the Coolant Temp reaches 75°C (167°F) or more.
(f) Read the MAF with the engine in an idling condition and at an engine speed of 2500 rpm.
Standard:
MAF while engine idling: Between 4.0 g/sec. and 8.0 g/sec. (shift lever: N; A/C: OFF).
MAF at engine speed of 2500 rpm: Between 10.0 g/sec. and 20.0 g/sec. (shift lever: N; A/C: OFF).
|
|
4. |
READ VALUE USING TECHSTREAM (COOLANT TEMP) |
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON.
(c) Turn the Techstream ON.
(d) Enter the following menus: Powertrain / Engine / Data List / All Data / Coolant Temp.
(e) 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 100°C (167°F and 212°F).
|
|
5. |
CHECK PCV HOSE CONNECTIONS |
(a) Check the PCV hose connections.
OK:
PCV hose is connected correctly and is not damaged.
|
|
6. |
CHECK AIR INDUCTION SYSTEM |
(a) Check the air induction system for vacuum leak
.
OK:
No leak from air induction system.
|
|
7. |
CHECK FOR SPARKS AND IGNITION
|
|
|
8. |
CHECK FOR EXHAUST GAS LEAK |
(a) Check for exhaust gas leak.
OK:
No gas leak.
|
|
9. |
CHECK FUEL PRESSURE |
(a) Check the fuel pressure
.
|
|
10. |
INSPECT FUEL INJECTOR (INJECTION AND VOLUME) |
(a) Check the injection volume
.
|
|
11. |
INSPECT AIR-FUEL RATIO SENSOR (HEATER RESISTANCE)
|
|
|
12. |
INSPECT INTEGRATION RELAY (A/F RELAY)
|
|
|
13. |
CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)
|
|
|
14. |
REPLACE AIR FUEL RATIO SENSOR |
(a) Replace the air fuel ratio sensor
.
|
|
15. |
PERFORM CONFIRMATION DRIVING PATTERN |
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON.
(c) Turn the Techstream ON.
(d) Clear DTCs
.
(e) Switch the ECM from normal mode to check mode using the Techstream
.
(f) Start the engine and warm it up with all the accessories switched OFF.
(g) Drive the vehicle at between 60 km/h and 120 km/h (38 mph and 75 mph) and at an engine speed of between 1400 rpm and 3200 rpm for 3 to 5 minutes.
HINT:
If the system is still malfunctioning, the MIL will be illuminated during step (f).
NOTICE:
If the conditions in this test are not strictly followed, no malfunction will be detected.
|
|
16. |
CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175) |
(a) Enter the following menus: Powertrain / Engine / Trouble Codes.
(b) Read DTCs.
Result
|
Result |
Proceed to |
|---|---|
|
No DTC is output |
A |
|
P0171, P0172, P0174 or P0175 is output |
B |
|
|
|