2001 TOYOTA SEQUOIA relay

± DIAGNOSTICSENGINE
DI±95
289 Author: Date:
2005 SEQUOIA (RM1146U)DTC No.
DTC Detecting ConditionTrouble Area
P0037Heater current is 0.25 A or less when the heater operates with

Open in heater circuit of heated oxygen sensor

Heated ox
ygen sensor heaterP0037
P0057
Heater current is 0.25 A or less when the heater o erates with
more than 10.5 V positive battery voltage

Heated oxygen sensor heater

EFI relay

ECM
P0038
P0058When heater operates, heater current exceeds 2.0 A

Short in heater circuit of heated oxygen sensor

Heated oxygen sensor heater

EFI relay

ECM
HINT:

Bank 1 refers to bank that includes cylinder No. 1.

Bank 2 refers to bank that does not includes cylinder No. 1.

Sensor 1 refers to the sensor closer to the engine assembly.

Sensor 2 refers to the sensor farther away from the engine assembly.
MONITOR DESCRIPTION
The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect oxygen
concentration in the exhaust. If the zirconia element is at the proper temperature and difference of the oxy-
gen concentration between the inside and outside surface of sensor is large, the zirconia element will gener-
ate voltage signals. In order to increase the oxygen concentration detecting capacity in the zirconia element,
the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor. When
current in the sensor is out of the standard operating range, the ECM interprets this as a fault in the heated
oxygen sensor and sets a DTC.
Example:
The ECM will set a high current DTC if the current in the sensor is more than 2.0 A when the heater is OFF.
Similarly, the ECM will set a low current DTC if the current is less than 0.3 A when the heater is ON.
MONITOR STRATEGY
P0037Rear HO2S heater (Bank 1) range check (Low
Current)
RltdDTC
P0038Rear HO2S heater (Bank 1) range check (High
Current)
Related DTCs
P0057Rear HO2S heater (Bank 2) range check (Low
Current)
P0058Rear HO2S heater (Bank 2) range check (High
Current)
Rid / tMain sensors/componentsHO2S heaterRequired sensors/componentsRelated sensors/componentsVehicle speed sensor (VSS)
Frequency of operationContinuous
Duration0.3 sec.
MIL operationImmediate
Sequence of operationNone

A23550
Battery 2FECM
OX1B HT2B
OX2B 33 Y
AG±R 3 2
ERB±W
EDW±B
5
4
5 1
22J2
IG4
HTR2
NTL2 OXR2
E8
F10
Fusible Link
Block G±R
EC 2D112H6
2A2 EFI Relay
EFI No. 1
EFI No. 2
J/C
IA4
G±R
HT1B 8
5
18
E8 E7
E7 E4
G±R G±R14
IA4 B±W
OXL21 4
A G±R Engine Room J/B
J42
J/CA
B J5
J/CW±R
E8
E6 G±W
BR
BR
H4 Heated Oxygen Sensor
(Bank 2 Sensor 2)
H2 Heated Oxygen Sensor
(Bank 1 Sensor 2)
J16
28
1 (Shielded) B
E B
EB J42
J/C G±W G±W
E1B
GJ/C
E1 +B
+B
E1 E2 MREL
(Shielded)
CC
C
BR DI±98
± DIAGNOSTICSENGINE
292 Author: Date:
2005 SEQUOIA (RM1146U)
WIRING DIAGRAM

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

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
H24254
Engine Room R/B:
EFI Relay
± DIAGNOSTICSENGINE
DI±101
295 Author: Date:
2005 SEQUOIA (RM1146U)
4 Check for open and short in harness and connector between ECM and heated
oxygen sensor, heated oxygen sensor ± EFI relay.
PREPARATION:
(a) Turn the ignition switch to OFF.
(b) Disconnect the H2 or H4 oxygen sensor connector.
(c) Disconnect the E7and E8 ECM connector.
CHECK:
Check the resistance.
OK:
Standard (Check for open):
Tester ConnectionsSpecified Conditions
HTL2 (H2±1) ± HT1B (E8±1)Below 1 W
HTR2 (H4±1) ± HT2B (E7±5)Below 1 W
Standard (Check for short):
Tester ConnectionsSpecified Conditions
HTL2 (H2±1) or HT1B (E8±1) ±
Body ground10 kW or higher
HTR2 (H4±1) or HT2B (E7±5) ±
Body ground10 kW or higher
PREPARATION:
(a) Turn the ignition switch to OFF.
(b) Disconnect the H2 or H4 oxygen sensor connector.
(c) Remove EFI relay from engine room R/B.
CHECK:
Check the resistance.
OK:
Standard (Check for open):
Tester ConnectionsSpecified Conditions
+B (A21±2) ±EFI relay (3)
+B (A22±2) ± EFI relay (3)Below 1 W
Standard (Check for short):
Tester ConnectionsSpecified Conditions
+B (H2±2) or EFI relay (3) ± Body ground
+B (H2±2) or EFI relay (3) ± Body ground10 kW or higher
NG Repair or replace harness or connector.
OK
Check for intermittent problems
(See page DI±11).

F10
Fusible
Link
Block
A23554
ECM
VG
E2G 8
E4
30
E8
29
E8 B±W R±W
2
B IA414
BatteryB 2F1 2D1 Engine Room J/B
EFI No. 1 EFI Relay
EFI No. 2
5
3
1
2 2H2A2G±R J2
J/C
A
B G±R
IG422
G±R
3 IA44B±W
J16
J/C
6B
W±B G±RA
A
J5
J/C
ED
+B
VG
MREL
M1
Mass Air Flow Meter
B±W
G±R
1
4
5 E2G DI±104
± DIAGNOSTICSENGINE
298 Author: Date:
2005 SEQUOIA (RM1146U)
COMPONENT OPERATING RANGE
ParameterStandard Value
Mass air flow meter voltage0.4 to 2.2 V
WIRING DIAGRAM

A21375
Engine Room J/B:
EFI
No. 2 Fuse
A21226
Wire Harness Side:
Mass Air Flow Meter Connector
M1
+B
A21376
Engine Room J/B:
EFI Relay
DI±108
± DIAGNOSTICSENGINE
302 Author: Date:
2005 SEQUOIA (RM1146U)
5 Check for open and short in harness and connector between mass air flow meter
and EFI relay.
PREPARATION:
Remove the EFI No. 2 fuse from the engine room J/B.
CHECK:
Check the resistance in the EFI No. 2 fuse.
OK:
Standard:
Below 1 W
PREPARATION:
(a) Install the EFI No. 2 fuse.
(b) Disconnect the M1 mass air flow meter connector.
(c) Remove the EFI relay from the engine room J/B.
CHECK:
Check the resistance between the wire harness side connec-
tors.
OK:
Standard:
Tester ConnectionSpecified Condition
+B (M1±1) ± Engine Room J/B (EFI
relay terminal 1)Below 1 W
+B (M1±1) or Engine room J/B (EFI relay
terminal 1) ± Body ground10 kW or higher
NG Repair or replace harness or connector.
OK
Check ECM power source circuit
(See page DI±493).

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

A19288
EFI Relay
± DIAGNOSTICSENGINE
DI±163
357 Author: Date:
2005 SEQUOIA (RM1146U)
16 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