Page 289 of 4323

± 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
Page 290 of 4323

DI±96
± DIAGNOSTICSENGINE
290 Author: Date:
2005 SEQUOIA (RM1146U)
TYPICAL ENABLING CONDITIONS
ItSpecificationItemMinimumMaximum
The monitor will run whenever these
DTCs are not presentSee page DI±18
P0037, P0057 (Low current):
Battery voltage10.5 V±
All heater is turned OFF and intrusive
heating is operated when the following
conditions are met
Condition (a) and (b)
(a) HeaterON
(b) Heater current±0.3 A
P0038, P0058 (High current):
Case 1:
Battery voltage10.5 V±
EngineRunning
StarterOFF
Intrusive heatingNot operating
Case 2:
Battery voltage10.5 V±
All heater is turned OFF and intrusive
heating is operated when the following
conditions are met
Condition (a) and (b)
(a) HeaterON
(b) Heater current2 A±
TYPICAL MALFUNCTION THRESHOLDS
Detection CriteriaThreshold
P0037, P0057 (Low current):
HO2S heater current during intrusive heatingLess than 0.3 A (when battery voltage is 10.5 V or more)
P0038, P0058 (High current):
Case 1:
HO2S heater current2 A or more
Case 2:
HO2S heater current during intrusive heatingMore than 2 A
COMPONENT OPERATING RANGE
ParameterStandard Value
HO2S heater current0.4 to 1 A (at idle, warmed±up engine and +B: 11 to 14 V)
Page 291 of 4323

± 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
Page 292 of 4323
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
Page 293 of 4323

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
Page 294 of 4323
B17411
HT1B
E7HT2B
E8
DI±100
± DIAGNOSTICSENGINE
294 Author: Date:
2005 SEQUOIA (RM1146U)
3 Check voltage between terminals HT1B, HT2B of ECM connectors and body
ground.
PREPARATION:
Turn the ignition switch ON.
CHECK:
Measure the voltage between terminals of the ECM connectors
and body ground.
HINT:
Connect terminal HT1B to the bank 1 sensor 2.
Connect terminal HT2B to the bank 2 sensor 2.
OK:
Standard:
Tester ConnectionSpecified Condition
HT1B (E8±1) ± Body ground9 to 14 V
HT2B (E7±5) ± Body ground9 to 14 V
OK Replace ECM (See page SF±80).
NG
Page 295 of 4323

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).
Page 296 of 4323

FI6929A09074A09707
Power Transistor
Output
Voltage
AB B+
Temperature Sensor
Platinum Hot Wire
Temperature Sensor
Platinum Hot Wire DI±102
± DIAGNOSTICSENGINE
296 Author: Date:
2005 SEQUOIA (RM1146U)
DTC P0100 Mass or Volume Air Flow Circuit
DTC P0102 Mass or Volume Air Flow Circuit Low Input
DTC P0103 Mass or Volume Air Flow Circuit High Input
CIRCUIT DESCRIPTION
The Mass Air Flow (MAF) meter measures the amount of air flowing through the throttle valve. The ECM uses
this information to determine the fuel injection time and provide a proper air fuel ratio. Inside the MAF meter,
there is a heated platinum wire exposed to the flow of intake air.
By applying a specific current to the wire, the ECM heats this wire to a given temperature. The flow of incom-
ing air cools the wire and an internal thermistor, affecting their resistance. To maintain a constant current
value, the ECM varies the voltage applied to these components in the MAF meter. The voltage level is pro-
portional to the airflow through the sensor. The ECM interprets this voltage as the intake air amount.
The circuit is constructed so that the platinum hot wire and temperature sensor provide a bridge circuit, with
the power transistor controlled so that the potential of A and B remains equal to maintain the set temperature.
DTC No.DTC Detection ConditionTrouble Area
P0100Open or short in mass air flow meter circuit for more than 3
sec.
P0102Open or short in mass air flow meter circuit for more than 3
sec.Open or short in mass air flow meter circuit
Mass air flow meter
P0103
Open in mass air flow meter circuit for more than 3 sec. (EVG
circuit)
Short in mass air flow meter circuit for more than 3 sec. (+B
circuit)Mass air flow meter
ECM
DICEN±02