2001 TOYOTA SEQUOIA heater

± DIAGNOSTICSENGINE
DI±97
291 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 (see page DI±27).

TID (Test Identification Data) is assigned to each emissions±related component.

TLT (Test Limit Type):
If TLT is 0, the component is malfunctioning when the test value is higher than the test limit.
If TLT is 1, the component is malfunctioning when the test value is lower than the test limit.

CID (Component Identification Data) is assigned to each test value.

Unit Conversion is used to calculate the test value indicated on generic tools.
TID $04: HO2S heater
TLTCIDUnit ConversionDescription of Test DataDescription of Test Limit
1$02Multiply by 0.000076
(A)Maximum HO2S heater current
(Bank 1 Sensor 2)Malfunction threshold for HO2S heater
1$20Multiply by 0.000076
(A)Maximum HO2S heater current
(Bank 2 Sensor 2)Malfunction threshold for HO2S heater

A21341
+B
OX E1HT
H2
H4
Components Side:
Bank 1 Sensor 2, Bank 2 Sensor 2
A19288
EFI Relay
± DIAGNOSTICSENGINE
DI±99
293 Author: Date:
2005 SEQUOIA (RM1146U)
INSPECTION PROCEDURE
HINT:
Read freeze frame data using hand±held tester. Because freeze frame records the engine conditions when
the malfunction is detected. When troubleshooting, it is useful to determine 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.
1 Check resistance of heated oxygen sensor heater.
PREPARATION:
Disconnect the H2 or H4 heated oxygen sensor connector.
CHECK:
Measure resistance between terminals of the heated oxygen
sensor.
OK:
Standard:
Tester ConnectionSpecified Condition
HTL2 (H2±1) ± +B (H2±2)11 to 16 W (20°C)
HTR2 (H4±1) ± +B (H4±2)11 to 16 W (20°C)
NG Replace heated oxygen sensor.
OK
2 Check EFI relay.
PREPARATION:
Remove the EFI relay from the engine room J/B.
CHECK:
Inspect the EFI relay.
OK:
Standard:
Terminal No.ConditionSpecified Condition
3 ± 5Always10 KW or higher
3 ± 5Apply B+ between
terminals 1 and 2Below 1 W
NG Replace EFI relay.
OK

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

+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.

B17416HT1BECM Connector
E7OX1B E8
HT2B
OX2B
A21341
+B
OX E1HT
H2
H4
Components Side:
Bank 1 Sensor 2, Bank 2 Sensor 2
DI±158
± DIAGNOSTICSENGINE
352 Author: Date:
2005 SEQUOIA (RM1146U)
3 Check for short in harness and connector between terminal OX1B and HT1B,
OX2B and HT2B of ECM.
PREPARATION:
(a) Turn the ignition switch to OFF and wait for 5 minutes.
(b) Disconnect the E7 and E8 ECM connector.
CHECK:
(a) Check the resistance.
OK:
Standard:
Tester ConnectionsSpecified Conditions
HT1B (E8±1) ± OX1B (E8±18)10 kW or higher
HT2B (E7±5) ± OX2B (E5±33)10 kW or higher
OK Replace ECM (See page SF±80
NG
4 Check resistance of heated oxygen sensor heater.
PREPARATION:
Disconnect the heated oxygen sensor connector.
CHECK:
Measure resistance between terminals of the heated oxygen
sensor.
OK:
Standard:
Tester ConnectionSpecified Condition
HT (1) ± +B (2)11 to 16 W at 20°C (68°F)
+B (2) ± OX (3)10 kW or higher
NG Replace heated oxygen sensor.
OK
Repair or replace harness or connector.
5 Perform confirmation driving pattern.
NEXT

A23543
+B
OXR2
OXL2E1 HTR2
HTL2
H2
H4
Wire Harness Side:
Bank 1 Sensor 2, Bank 2 Sensor 2
B17416HT1BECM Connector E7OX1B E8
HT2B
OX2B
A21040
Reference (Bank 1 Sensor 1 System Drawing)
From
BatteryEFI No. 1 FuseEFI Relay
EFI No. 2 FuseHeater Oxygen
Sensor
Heater
SensorHT1A
OX1A
E2
MRELECM
DI±164
± DIAGNOSTICSENGINE
358 Author: Date:
2005 SEQUOIA (RM1146U)
17 Check for open and short in harness and connector between ECM and heated
oxygen sensor.
PREPARATION:
(a) Disconnect the heated oxygen sensor connector.
(b) Disconnect the E7 and E8 ECM connector.
CHECK:
Measure the resistance between the wire harness side connec-
tors.
OK:
Standard:
Tester ConnectionSpecified Condition
OXL2 (H2±3) ± OX1B (E8±18)Below 1 W
HTL2 (H2±1) ± HT1B (E8±1)Below 1 W
OXR2 (H4±3) ± OX2B (E7±33)Below 1 W
HTR2 (H4±1) ± HT2B (E7±5)Below 1 W
OXL2 (H2±3) or OX1B (E8±18) ±
Body ground10 kW or higher
HTL2 (H2±1) or HT1B (E8±1) ±
Body ground10 kW or higher
OXR2 (H4±3) or OX2B (E7±33) ±
Body ground10 kW or higher
HTR2 (H4±1) or HT2B (E7±5) ±
Body ground10 kW or higher
NG Repair or replace harness or connector.
OK
Replace heated oxygen sensor.

DI±166
± DIAGNOSTICSENGINE
360 Author: Date:
2005 SEQUOIA (RM1146U)DTC No.
DTC Detecting ConditionTrouble Area
P0171
P0174When air±fuel ratio feedback is stable after warming up the
engine, fuel trim is considered to be in error on LEAN side
(2 trip detection logic)

Air induction system

Injector blockage

Mass air flow meter

Engine coolant temperature sensor

Fuel pressure

Gas leakage in exhaust system

Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit

Heated oxygen sensor (bank 1, 2 sensor 1)

Heated oxygen sensor heater (bank 1, 2 sensor 1)

EFI relay

PCV piping

ECM
P0172
P0175When air±fuel ratio feedback is stable after warming up the
engine, fuel trim is considered to be in error on RICH side
(2 trip detection logic)

Injector leak, blockage

Mass air flow meter

Engine coolant temperature sensor

Ignition system

Fuel pressure

Gas leakage in exhaust system

Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit

Heated oxygen sensor (bank 1, 2 sensor 1)

ECM
HINT:

When DTC P0171 or P0174 is recorded, the actual air±fuel ratio is on the LEAN side. When DTC
P0172 or P0175 is recorded, 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 recorded.
The MIL then comes on.

If the total of the short±term fuel trim value and long±term fuel trim value is within
35 % (engine cool-
ant temperature is more than 75 C (167F)), the system is functioning normally.