2001 TOYOTA SEQUOIA O2 sensor

DI±140
± DIAGNOSTICSENGINE
334 Author: Date:
2005 SEQUOIA (RM1146U)
TYPICAL ENABLING CONDITIONS
ItSpecificationItemMinimumMaximum
The monitor will run whenever this DTC is
not presentSee page DI±18
Fuel cutOFF
EngineRunning
TYPICAL MALFUNCTION THRESHOLDS
Detection CriteriaThreshold
Time until ºengine coolant temperatureº detection temperature reaches feedback start temperature
When the temperature at the time of engine starting is
±8.34°C (17°F) or moreEngine coolant temperature is less than ºclosed±loop enable temperatureº
when 2 min. or more after engine start
When the temperature at the time of engine starting is
±19.45 to ±8.34°C (±3 to 17°F)Engine coolant temperature is less than ºclosed±loop enable temperatureº
when 5 min. or more after engine start
When the temperature at the time of engine starting is
±19.45°C (±3°F) or lessEngine coolant temperature is less than ºclosed±loop enable temperatureº
when 20 min. or more after engine start
INSPECTION PROCEDURE
HINT:

If DTC P0115, P0116, P0117, P0118 and P0125 are output simultaneously, engine coolant tempera-
ture sensor circuit may be open or short. Perform the troubleshooting of DTC P0115, P0117 or P0118
first.

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, as well as other data from the time when a malfunction occurred.
1 Are there any other codes (besides DTC P0125) being output?
PREPARATION:
(a) Connect the hand±held tester to the DLC3.
(b) Turn the ignition switch ON and push the hand±held tester main switch ON.
(c) When using hand±held tester, enter the following menu: DIAGNOSIS / ENHANCED OBD II / DTC
INFO / CURRENT CODES.
CHECK:
Read the DTCs using the hand±held tester.
RESULT:
Display (DTC output)Proceed to
P0125A
ºP0125º and other DTCsB
HINT:
If any other codes besides ºP0125º are output, perform the troubleshooting for those DTCs first.
B Go to relevant DTC chart (See page DI±58).
A

± DIAGNOSTICSENGINE
DI±141
335 Author: Date:
2005 SEQUOIA (RM1146U)
2 Inspect thermostat (See page CO±12).
CHECK:
Check the valve opening temperature of the thermostat.
OK:
Valve opening temperature is 80 to 84C (176 to 183F)
HINT:
Also check that the valve is completely closed under opening temperature as above.
NG Replace thermostat (See page CO±11).
OK
3 Check cooling system.
CHECK:
Check that there is detect in the cooling system which causes overcool, such as abnormal radiator fan opera-
tion, modified cooling system and so on.
NG Repair or replace cooling system.
OK
Replace engine coolant temperature sensor.

A20488A21045
Threshold
(75C (167F))Estimated ECT
5 sec.
Indicated coolant temp. reading
DTC set (after 2 driving cycle) ECT
Time DI±142
± DIAGNOSTICSENGINE
336 Author: Date:
2005 SEQUOIA (RM1146U)
DTC P0128 Coolant Thermostat (Coolant Temperature
Below Thermostat Regulating Temperature)
HINT:
This is the purpose of ºthermostatº malfunction detection.
CIRCUIT DESCRIPTION
If the engine coolant temperature does not reach 75°C (167°F) despite sufficient warm±up time has
elapsed.
DTC No.DTC Detection conditionTrouble Area
P0128
Condition (a), (b) and (c) are met:
(a) Cold start
(b) After sufficient warm±up time has elapsed
(c) Engine coolant temperature greater than 75°C (167°F)
Thermostat

Cooling system

Engine coolant temperature sensor

ECM
MONITOR DESCRIPTION
The ECM estimates the coolant temperature based on starting temperature, engine loads, and engine
speeds. The ECM then compares the estimated temperature with the actual ECT (Engine Coolant Tempera-
ture). When the estimated coolant temperature reaches 75C (167F), the ECM checks the actual ECT. If
the actual ECT is less than 75C (167F), the ECM will interpret this as a fault in the thermostat or engine
cooling system and set a DTC.
DICEQ±02

± DIAGNOSTICSENGINE
DI±143
337 Author: Date:
2005 SEQUOIA (RM1146U)
MONITOR STRATEGY
Related DTCsP0128Thermostat
Rid / t
Main sensors/componentsEngine coolant temperature sensor, Engine
cooling system, Thermostat
Required sensors/components
Related sensors/componentsIntake air temperature sensor, Vehicle speed
sensor
Frequency of operationOnce per driving cycle
Duration15 min.
MIL operation2 driving cycles
Sequence of operationNone
TYPICAL ENABLING CONDITIONS
ItSpecificationItemMinimumMaximum
The monitor will run whenever this DTC is
not presentSee page DI±18
Battery voltage11.0 V±
Throttle position learningCompleted
Either of the following conditions is metCondition 1 or 2
1. All of the following conditions are metCondition (a), (b) and (c)
(a) ECT at engine start ± IAT at engine
start±15 to 7C (±27 to 12.6F)
(b) ECT at engine start±10 to 56C (14 to 133F)
(c) IAT at engine start±10 to 56C (14 to 133F)
2. All of the following conditions are metCondition (a), (b) and (c)
(a) ECT at engine start ± IAT at engine
start±7C (12.6F)±
(b) ECT at engine start±56C (133F)
(c) IAT at engine start±10C (14F)±
Accumulated time that vehicle speed is 80
mph (128 km/h) or more±20 sec.
TYPICAL MALFUNCTION THRESHOLDS
Detection CriteriaThreshold
Duration that both of following conditions 1 and 2 are met5 sec. or more
1. Estimated engine coolant temperature75C (167F) or more
2. Engine coolant temperature sensor outputLess than 75C (167F)
COMPONENT OPERATING RANGE
ParameterStandard Value
Engine coolant temperature sensor output value after warm
up75C (167F) or more

DI±144
± DIAGNOSTICSENGINE
338 Author: Date:
2005 SEQUOIA (RM1146U)
MONITOR RESULT
Refer to page DI±26 for detailed information.
The test value and test limit information are described as shown in the following table. Check the monitor
result and test values after performing the monitor drive pattern (refer to ºConfirmation Monitorº).

MID (Monitor Identification Data) is assigned to each emissions±related component.

TID (Test Identification Data) is assigned to each test value.

Scaling is used to calculate the test value indicated on generic OBD ll scan tools.
Thermostat
MIDTIDScalingDescription of Test ValueMinimum Test LimitMaximum Test Limit
$E1$E8Multiply by 0.1
(°C)ECT sensor output when estimated
ECT reached to malfunction criteriaMalfunction criterionMaximum test limit
INSPECTION PROCEDURE
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, as well as other
data from the time when a malfunction occurred.
1 Are there any other codes (besides DTC P0128) being output?
PREPARATION:
(a) Connect the hand±held tester to the DLC3.
(b) Turn the ignition switch ON and push the hand±held tester main switch ON.
(c) When using hand±held tester, enter the following menu: DIAGNOSIS / ENHANCED OBD II / DTC
INFO / CURRENT CODES.
CHECK:
Read the DTC using the hand±held tester.
RESULT:
Display (DTC Output)Proceed to
P0128A
P0128 and other DTCsB
HINT:
If any other codes besides P0128 are output, perform the troubleshooting for those DTCs first.
B Go to relevant DTC chart (See page DI-58).
A

DI±146
± DIAGNOSTICSENGINE
340 Author: Date:
2005 SEQUOIA (RM1146U)
DTC P0136 Oxygen Sensor Circuit Malfunction (Bank 1
Sensor 2)
DTC P0137 Oxygen Sensor Circuit Low Voltage (Bank 1
Sensor 2)
DTC P0138 Oxygen Sensor Circuit High Voltage (Bank 1
Sensor 2)
DTC P0156 Oxygen Sensor Circuit Malfunction (Bank 2
Sensor 2)
DTC P0157 Oxygen Sensor Circuit Low Voltage (Bank 2
Sensor 2)
DTC P0158 Oxygen Sensor Circuit High Voltage (Bank 2
Sensor 2)
HINT:
Sensor 2 refers to the sensor mounted behind the Three±Way Catalytic Converter (TWC) and located far
from the engine assembly.
CIRCUIT DESCRIPTION
In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide
(NOx) components in the exhaust gas, a TWC is used. For the most efficient use of the TWC, the air±fuel
ratio must be precisely controlled so that it is always close to the stoichiometric air±fuel level. For the purpose
of helping the ECM to deliver accurate air±fuel ratio control, a Heated Oxygen (HO2) sensor is used.
The HO2 sensor is located behind the TWC, and detects the oxygen concentration in the exhaust gas. Since
the sensor is integrated with the heater that heats the sensing portion, it is possible to detect the oxygen
concentration even when the intake air volume is low (the exhaust gas temperature is low).
When the air±fuel ratio becomes lean, the oxygen concentration in the exhaust gas is rich. The HO2 sensor
informs the ECM that the post±TWC air±fuel ratio is lean (low voltage, i.e. less than 0.45 V).
Conversely, when the air±fuel ratio is richer than the stoichiometric air±fuel level, the oxygen concentration
in the exhaust gas becomes lean. The HO2 sensor informs the ECM that the post±TWC air±fuel ratio is rich
(high voltage, i.e. more than 0.45 V). The HO2 sensor has the property of changing its output voltage drasti-
cally when the air±fuel ratio is close to the stoichiometric level.
The ECM uses the supplementary information from the HO2 sensor to determine whether the air±fuel ratio
after the TWC is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is work-
DIDFR±01

B17386
Housing
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Exhaust Gas CoverIdeal Air±Fuel Mixture
Output Voltage
Richer ± Air Fuel Ratio ± Leaner
Atmospheric Air
± DIAGNOSTICSENGINE
DI±147
341 Author: Date:
2005 SEQUOIA (RM1146U)
ing improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the primary
air±fuel ratio control.
DTC No.DTC Detecting ConditionTrouble Area
P0136
P0156
During active air±fuel ratio control, following conditions (a) and
(b) met for certain period of time (2 trip detection logic):
(a) Heated Oxygen (HO2) sensor voltage does not decrease to
less than 0.2 V
(b) HO2 sensor voltage does not increase to more than 0.6 V

Open or short in HO2 sensor (sensor 2) circuit

HO2 sensor (sensor 2)

HO2 sensor heater (sensor 2)

Air±Fuel Ratio (A/F) sensor (sensor 1)
P0136
P0156Sensor impedance less than 5 W for more than 30 seconds
when ECM presumes sensor to being warmed up and operat-
ing normally (1 trip detection logic)
Air Fuel Ratio (A/F) sensor (sensor 1)

EFI relay

Gas leakage from exhaust system
P0137
P0157
During active air±fuel ratio control, following conditions (a) and
(b) met for certain period of time (2 trip detection logic):
(a) HO2 sensor voltage output less than 0.21 V
(b) Target air±fuel ratio rich

Open in HO2 sensor (sensor 2) circuit

HO2 sensor (sensor 2)

HO2 sensor heater (sensor 2)
P0137
P0157
High impedance:
Sensor impedance 348.1 MW or more for more than 90 se-
conds when ECM presumes sensor to being warmed up and
operating normally (1 trip detection logic)
HO2 sensor heater (sensor 2)

EFI relay

Gas leakage from exhaust system
P0138
P0158
During active air±fuel ratio control, following conditions (a) and
(b) met for certain period of time (2 trip detection logic):
(a) HO2 sensor voltage output 0.59 V or more
(b) Target air±fuel ratio lean

Short in HO2 sensor (sensor 2) circuit

HO2 sensor (sensor 2)

ECM internal circuit malfunctionP0138
P0158HO2 sensor voltage output exceeds 1.2 V for more than 30
seconds (1 trip detection logic)
ECM internal circuit malfunction

B17387
Active air±fuel
ratio control
OffOperation15 to 20 seconds
HO2 sensor
voltage
Abnormal Normal
0.21 V 0.59 V HO2 SENSOR CIRCUIT MALFUNCTION (P0136, P0156: ABNORMAL VOLTAGE) DI±148
± DIAGNOSTICSENGINE
342 Author: Date:
2005 SEQUOIA (RM1146U)
MONITOR DESCRIPTION
Active Air±Fuel Ratio Control
The ECM usually performs air±fuel ratio feedback control so that the Air±Fuel Ratio (A/F) sensor output indi-
cates a near stoichiometric air±fuel level. This vehicle includes active air±fuel ratio control in addition to regu-
lar air±fuel ratio control. The ECM performs active air±fuel ratio control to detect any deterioration in the
Three±Way Catalytic Converter (TWC) and Heated Oxygen (HO2) sensor malfunctions (refer to the diagram
below).
Active air±fuel ratio control is performed for approximately 15 to 20 seconds while driving with a warm engine.
During active air±fuel ratio control, the air±fuel ratio is forcibly regulated to become lean or rich by the ECM.
If the ECM detects a malfunction, one of the following DTCs is set: DTC P0136, P0156 (abnormal voltage
output), P0137, P0157 (open circuit) and P0138, P0158 (short circuit).
Abnormal Voltage Output of HO2 Sensor (DTC P0136, P0156)
While the ECM is performing active air±fuel ratio control, the air±fuel ratio is forcibly regulated to become
rich or lean. If the sensor is not functioning properly, the voltage output variation is small. For example, when
the HO2 sensor voltage does not decrease to less than 0.21 V and does not increase to more than 0.59 V
during active air±fuel ratio control, the ECM determines that the sensor voltage output is abnormal and sets
DTC P0136.