2001 TOYOTA SEQUOIA Service Repair Manual

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Page 337 of 4323

TOYOTA SEQUOIA 2001 Service Repair Manual ± DIAGNOSTICSENGINE
DI±143
337 Author: Date:
2005 SEQUOIA (RM1146U)
MONITOR STRATEGY
Related DTCsP0128Thermostat
Rid / t
Main sensors/componentsEngine coolant temperature sensor, Engine
cooling

Page 338 of 4323

TOYOTA SEQUOIA 2001 Service Repair Manual 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

Page 339 of 4323

TOYOTA SEQUOIA 2001 Service Repair Manual ± DIAGNOSTICSENGINE
DI±145
339 Author: Date:
2005 SEQUOIA (RM1146U)
2 Check cooling system.
CHECK:
(a) Check for defects in the cooling system that might cause the system to be too cold, such as

Page 340 of 4323

TOYOTA SEQUOIA 2001 Service Repair Manual 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)
DT

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

Page 341 of 4323

TOYOTA SEQUOIA 2001 Service Repair Manual 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 A

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

Page 342 of 4323

TOYOTA SEQUOIA 2001 Service Repair Manual 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
± DIAGNOS

Page 343 of 4323

TOYOTA SEQUOIA 2001 Service Repair Manual B17388
Active air±fuel
ratio control
Target air±fuel ratio
HO2 sensor
voltageStoichiometric
Air±Fuel Level
Rich
0.21 V
Active air±fuel
ratio control
Target air±fuel ratio
HO2 sensor
voltageL

Page 344 of 4323

TOYOTA SEQUOIA 2001 Service Repair Manual B17389Temperature C (F)
Impedance W
300 400 500 600 700 800
(572)5 10 100 1,000 15,000
(752) (932) (1,112) (1,292) (1,472)
DTC Detection Area Interrelation between temperature of
the element and im

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