2001 TOYOTA SEQUOIA fuel

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.

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).

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 impedance: DI±150
± DIAGNOSTICSENGINE
344 Author: Date:
2005 SEQUOIA (RM1146U)
High or Low Impedance of Heated Oxygen (HO2) Sensor (DTC P0136, P0156, P0137 or P0157)
During normal air±fuel ratio feedback control, there are small
variations in the exhaust gas oxygen concentration.
In order to
continuously monitor the slight variation of the HO2 sensor sig-
nal while the engine is running, the impedance* of the sensor
is measured by the ECM. The ECM determines that there is a
malfunction in the sensor when the measured impedance devi-
ates from the standard range.
*: The effective resistance in an alternating current electrical cir-
cuit.
HINT:

The impedance can not be measured using an ohmme-
ter.

DTC P0136 or P0156 indicates the deterioration of the
HO2 sensor. The ECM sets the DTC by calculating the im-
pedance of the sensor when the typical enabling condi-
tions are satisfied (1 driving cycle).

DTC P0137 or P0157 indicates an open circuit in the HO2
sensor (1 driving cycle). The ECM sets this DTC when the
impedance of the sensor exceeds the threshold 348.1
MW.

± 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

DI±152
± DIAGNOSTICSENGINE
346 Author: Date:
2005 SEQUOIA (RM1146U) A/F sensor status
Activated
Fuel±cutOFF
Engine load10 to 70%
Shift position4th±
Heated oxygen sensor impedance (Low):
Battery voltage11 V±
Estimated sensor temperature±700°C (1,292°F)
ECM monitorCompleted
P0606Not set
Heated oxygen sensor impedance (High):
Battery voltage11 V±
Estimated sensor temperature450°C (842°F)±
ECM monitorCompleted
P0606Not set
Heated oxygen sensor output voltage (Extremely high):
Battery voltage11 V±
Time after engine start2 sec.±
TYPICAL MALFUNCTION THRESHOLDS
Detection CriteriaThreshold
Heated oxygen sensor output voltage (Output voltage):
Either of the following conditions is met:Condition 1 or 2
1. All of the following conditions are met:Condition (a), (b) and (c)
(a) Commanded air±fuel ratio14.3 or less
(b) Rear HO2S voltage0.21 to 0.59 V
(c) OSC (Oxygen Storage Capacity of catalyst)3 g or more
2. All of the following conditions are met:Condition (a), (b) and (c)
(a) Commanded air±fuel ratio14.9 or more
(b) Rear HO2S voltage0.21 to 0.59 V
(c) OSC (Oxygen Storage Capacity of catalyst)3 g or more
Heated oxygen sensor output voltage (Low voltage):
All of the following conditions are met:Condition 1, 2 and 3
1. Commanded air±fuel ratio14.3 or less
2. Rear HO2S voltageLess than 0.21 V
3. OSC (Oxygen Storage Capacity of catalyst)3 g or more
Heated oxygen sensor output voltage (High voltage):
All of the following conditions are met:Condition 1, 2 and 3
1. Commanded air±fuel ratio14.9 or more
2. Rear HO2S voltageMore than 0.59 V
3. OSC (Oxygen Storage Capacity of catalyst)3 g or more
Heated oxygen sensor impedance (Low):
Duration of following condition30 sec. or more
Heated oxygen sensor impedanceLess than 5 W
Heated oxygen sensor impedance (High):
Duration of following condition90 sec. or more

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.

+25 %
±12.5 %
More than 0.5 V
Less than 0.4 V
Case 1
Case 2
Case 3
Case 4
Output voltage of A/F sensor
(sensor 1: front sensor)
Injection volume
Output voltage
Output voltage of heated oxygen
sensor (sensor 2: rear sensor)Mainly suspected
trouble area
OK
+25 %
±12.5 %
More than 0.5 V
Less than 0.4 V
Injection volume
Output voltage
+25 %
±12.5 %
More than 0.5 V
Less than 0.4 V
Injection volume
Output voltage
Sensor 1: front sensor
(sensor 1, heater, sensor 1
circuit)
+25 %
±12.5 %
More than 0.5 V
Less than 0.4 V
Injection volume
Output voltage
+25 %
±12.5 %
Injection volume
Output voltage
NG
+25 %
±12.5 %
Injection volume
Output voltage
NG
+25 %
±12.5 %
Injection volume
Output voltage
NG
+25 %
±12.5 %
Injection volume
Output voltage
NGExtremely rich or lean actual
air±fuel ratio
(Injector, fuel pressure, gas
leakage in exhaust system,
etc.) OK
OK
OK
Almost
no reaction
'
Sensor 2: rear sensor
(sensor 2, heater, sensor 2
circuit)
Almost
no reactionAlmost
no reactionAlmost
no reaction
DI±156
± DIAGNOSTICSENGINE
350 Author: Date:
2005 SEQUOIA (RM1146U)
The following A/F CONTROL procedure enables the technician to check and graph the voltage output of
the heated oxygen sensors.
For displaying the graph indication, first enter ºACTIVE TEST / A/F CONTROL / USER DATA,º then select
ºA/F B1,2S1and O2S B1,2S2º by pressing ºYESº button, and push ºENTERº button before pressing ºF4º
button.
HINT:

If different DTCs that are related to different system are output simultaneously while terminal E2 is used
as a ground terminal, terminal E2 may be open.

Read freeze frame data using the hand-held tester. Freeze frame data records the engine conditions
when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle
was running or stopped, the engine was warmed up or not, the air±fuel ratio was lean or rich, etc. when
a malfunction occurred.