2001 TOYOTA SEQUOIA Page 18

± 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.

± 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

± 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 abnormal
radiator fan operation or a modified cooling system.
(b) 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 Repair or replace cooling system.
OK
3 Check thermostat (See page CO±12).
CHECK:
Check the valve lift.
OK:
Valve lift: 10 mm (0.39 in.) or more at 95°C (203°F)
NG Replace thermostat.
OK
Replace ECM (See page SF±80).

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
voltageLean HO2 SENSOR CIRCUIT LOW VOLTAGE (P0137, P0157: OPEN)
HO2 SENSOR CIRCUIT HIGH VOLTAGE (P0138, P0158: SHORT)OffOperation
OffNormal
Abnormal 15 to 20 seconds
0.59 VAbnormalAbnormal Normal
Operation
Stoichiometric
Air±Fuel Level
± DIAGNOSTICSENGINE
DI±149
343 Author: Date:
2005 SEQUOIA (RM1146U)
Open or Short in the Heated Oxygen (HO2) Sensor Circuit (DTC P0137, P0157, P0138 or P0158)
During active air±fuel ratio control, the ECM calculates the Oxygen Storage Capacity (OSC)* of the Three±
Way Catalytic Converter (TWC) by forcibly regulating the air±fuel ratio to become rich or lean.
If the HO2 sensor has an open or short, or the voltage output of the sensor noticeably decreases, the OSC
indicates an extraordinarily high value. Even if the ECM attempts to continue regulating the air±fuel ratio to
become rich or lean, the HO2 sensor output does not change.
While performing active air±fuel ratio control, when the target air±fuel ratio is rich and the HO2 sensor voltage
output is 0.21 V or less (lean), the ECM interprets this as an abnormally low sensor output voltage and sets
DTC P0137 or P0157. When the target air±fuel ratio is lean and the voltage output is 0.59 V or more (rich)
during active air±fuel ratio control, the ECM determines that the sensor voltage output is abnormally high,
and sets DTC P0138 or P0158.
HINT:
DTC P0138 or P0158 is also set if the HO2 sensor voltage output is more than 1.2 V for 30 seconds or more.
*: The TWC has the capability to store oxygen. The OSC and the emission purification capacity of the TWC
are mutually related. The ECM determines whether the catalyst has deteriorated, based on the calculated
OSC value (see page DI±249).

± DIAGNOSTICSENGINE
DI±151
345 Author: Date:
2005 SEQUOIA (RM1146U)
MONITOR STRATEGY
P0136
Heated rear oxygen sensor (Bank 1) output volt-
age (Output voltage)
P0136Heated rear oxygen sensor (Bank 1) impedance
(Low)
P0137
Heated rear oxygen sensor (Bank 1) output volt-
age (Low voltage)
P0137Heated rear oxygen sensor (Bank 1) impedance
(High)
P0138
Heated rear oxygen sensor (Bank 1) output volt-
age (High voltage)
RltdDTC
P0138Heated rear oxygen sensor (Bank 1) output volt-
age (Extremely high)
Related DTCs
P0156
Heated rear oxygen sensor (Bank 2) output volt-
age (Output voltage)
P0156Heated rear oxygen sensor (Bank 2) impedance
(Low)
P0157
Heated rear oxygen sensor (Bank 2) output volt-
age (Low voltage)
P0157Heated rear oxygen sensor (Bank 2) impedance
(High)
P0158
Heated rear oxygen sensor (Bank 2) output volt-
age (High voltage)
P0158Heated rear oxygen sensor (Bank 2) output volt-
age (Extremely high)
Rid / tMain sensors/componentsHeated rear oxygen sensorRequired sensors/componentsRelated sensors/componentsMass air flow meter
Frequency of operationOnce per driving cycle: Active air±fuel ratio control detection
Continuous: Others
Duration
20 sec.: Heated oxygen sensor output (Output voltage, High voltage, Low voltage)
30 sec.: Heated oxygen sensor impedance (Low)
90 sec.: Heated oxygen sensor impedance (High)
10 sec.: Heated oxygen sensor impedance (Extremely high)
MIL operation2 driving cycles Heated oxygen sensor output (Output voltage, High voltage, Low voltage)
Immediate: Heated oxygen sensor impedance (Low, High, Extremely high)
Sequence of operationNone
TYPICAL ENABLING CONDITIONS
ItSpecificationItemMinimumMaximum
The monitor will run whenever these
DTCs are not presentSee page DI±18
Heated oxygen sensor output voltage (Output voltage, High voltage and Low voltage):
Active air±fuel ratio controlExecuting
Active air±fuel ratio control being when all
of following conditions met±
Battery voltage11 V±
Engine coolant temperature75°C (167°F)±
IdleOFF
Engine RPM±3,200 rpm

± DIAGNOSTICSENGINE
DI±153
347 Author: Date:
2005 SEQUOIA (RM1146U) Heated oxygen sensor impedance
348.1 MW or more
Heated oxygen sensor output voltage (Extremely high):
Duration of following condition10 sec. or more
Heated oxygen sensor voltageMore than 1.2 V
COMPONENT OPERATING RANGE
ParameterStandard Value
Heated oxygen sensor voltageVaries between 0.1 to 0.9 V
MONITOR RESULT
Refer to page DI±24 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.
HO2S bank 1 sensor 2
MIDTIDScalingDescription of Test ValueMinimum Test LimitMaximum Test Limit
$02$07Multiply by 0.001
(V)Minimum sensor voltageMinimum test limitMaximum test limit
$02$08Multiply by 0.001
(V)Maximum sensor voltageMinimum test limitMaximum test limit
$02$8FMultiply by 0.001
(g)Maximum oxygen storage capacity0Maximum test limit
HO2S bank 2 sensor 2
MIDTIDScalingDescription of Test ValueMinimum Test LimitMaximum Test Limit
$06$07Multiply by 0.001
(V)Minimum sensor voltageMinimum test limitMaximum test limit
$06$08Multiply by 0.001
(V)Maximum sensor voltageMinimum test limitMaximum test limit
$06$8FMultiply by 0.001
(g)Maximum oxygen storage capacity0Maximum test limit
WIRING DIAGRAM
Refer to DTC P2195 on page DI±383.

A23661
Vehicle Speed
(64 km/h and 113 km/h)Between
40 mph and 70 mph
Idling
Ignition Switch OFF
10 minutes
Time Warm up
(Note: Even if vehicle stops during driving pattern, test can be resumed)NOTICE:
This test will not be completed
if the vehicle is driven under
absolutely constant speed
conditions such as with cruise
control activated. (h)
(g)
MISFIRE MON ..................... AVAILREADINESS TESTS
CAT EVAL ......................... INCMPL
HTD CAT EVAL ...................... N/A
EVAP EVAL ....................... INCMPL
2nd AIR EVAL .......................... N/A
A/C EVAL ................................ N/A
O2S EVAL ........................ INCMPL
O2S HTR EVAL .................. INCMPL
EGR EVAL ...............................N/A COMP MON ........................ AVAIL FUEL SYS MON ................... AVAIL
A76855
A23660
DI±154
± DIAGNOSTICSENGINE
348 Author: Date:
2005 SEQUOIA (RM1146U)
CONFIRMATION DRIVING PATTER
HINT:

This confirmation driving pattern is used in steps 5, 8 and 11 of the following diagnostic troubleshooting
procedure when using either a hand±held tester.

Performing this confirmation pattern will activate the Heated Oxygen (HO2) sensor monitor. (The cata-
lyst monitor is performed simultaneously.) This is very useful for verifying the completion of a repair.
(a) Connect a hand±held tester to the DLC3.
(b) Turn the ignition switch to ON.
(c) Turn the tester or scan tool ON.
(d) Clear DTCs (where set) (see page DI±43).
(e) If using a hand±held tester, select the following menu
items: DIAGNOSIS / CARB OBD II / READINESS
TESTS.
(f) Check that O2S EVAL is INCMPL (incomplete).
(g) Start the engine and warm it up.
(h) Drive the vehicle at between 40 mph and 70 mph (64 km/h
and 113 km/h) for at least 10 minutes.
(i) Note the state of the Readiness Tests items. Those items
will change to COMPL (complete) as O2S EVAL monitor
operates.
(j) On the tester, select the following menu items: DIAGNO-
SIS / ENHANCED OBD II / DTC INFO / PENDING
CODES and check if any DTCs (any pending DTCs) are
set.
HINT:
If O2S EVAL does not change to COMPL, and any pending
DTCs fail to set, extend the driving time.