2001 TOYOTA SEQUOIA Page 18

± DIAGNOSTICSENGINE
DI±89
283 Author: Date:
2005 SEQUOIA (RM1146U)
HINT:

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

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

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

Sensor 2 refers to the sensor farthest away from the engine assembly.
MONITOR DESCRIPTION
The ECM uses the Air±Fuel Ratio sensor (A/F sensor) information to regulate the air±fuel ratio close to the
stoichiometric ratio. This maximizes the catalytic converter's ability to purify exhaust gases. The sensor de-
tects oxygen levels in the exhaust gas and sends this signal to the ECM.
The inner surface of the sensor element is exposed to outside air. The outer surface of the sensor element
is exposed to exhaust gas. The sensor element is made of platinum coated zirconia and includes an inte-
grated heating element. The zirconia element generates a small voltage when there is a large difference in
the oxygen concentrations of the exhaust and the outside air. The platinum coating amplifies the voltage
generation. When heated, the sensor becomes very efficient. If the temperature of the exhaust is low, the
sensor will not generate useful voltage signals without supplemental heating. The ECM regulates the sup-
plemental heating using a duty±cycle approach to regulate the average current in the heater element. If the
heater current is out of the normal range, the sensor's output signals will be inaccurate and the ECM can
not regulate the air±fuel ratio properly.
When the heater current is out of the normal operating range, the ECM interprets this as a malfunction and
sets a DTC.
MONITOR STRATEGY
P0031A/F sensor heater (Bank 1) range check (Low
current)
RltdDTC
P0032A/F sensor heater (Bank 1) range check (High
current)
Related DTCs
P0051A/F sensor heater (Bank 2) range check (Low
current)
P0052A/F sensor heater (Bank 2) range check (High
current)
Rid / tMain sensors/componentsA/F sensor heaterRequired sensors/componentsRelated sensors/components±
Frequency of operationContinuous
Duration10 sec.
MIL operationImmediate
Sequence of operationNone
TYPICAL ENABLING CONDITIONS
ItSpecificationItemMinimumMaximum
The monitor will run whenever these
DTCs are not presentSee page DI±18
P0031, P0051 (Low current):
Battery voltage10.5 V±
A/F sensor heater duty ratio50%±
Time after engine start10 sec.±

B17396
HT +B
AF± AF+ Sensor 1A/F Sensor Component Side:
Front View
DI±90
± DIAGNOSTICSENGINE
284 Author: Date:
2005 SEQUOIA (RM1146U) P0032, P0052 (High current):
Time after engine start10 sec.±
TYPICAL MALFUNCTION THRESHOLDS
Detection CriteriaThreshold
P0031, P0051 (Low current):
A/F sensor heater currentLess than 0.8 A
P0032, P0052 (High current):
A/F sensor heater currentMore than 10 A
COMPONENT OPERATING RANGE
ParameterStandard Value
A/F sensor heater current1.8 to 3.4 A at 20°C (68°F)
WIRING DIAGRAM
Refer to DTC P2195 on page DI±383.
INSPECTION PROCEDURE
HINT:
Read freeze frame data using a hand±held tester or OBD II scan tool. Freeze frame data record the engine
condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if
the vehicle was moving or stationary, if the engine was warmed up or not, if the air±fuel ratio was lean or
rich, and other data, from the time the malfunction occurred.
1 Check resistance of air±fuel ratio (A/F) sensor heater.
PREPARATION:
Disconnect the air±fuel ratio (A/F) sensor connector.
CHECK:
Measure resistance between the terminals of the A/F sensor
connector.
OK:
Standard:
Tester ConnectionSpecified Condition
HT (1) ± +B (2)1.8 W to 3.4 W at 20C (68F)
HT (1) ± AF± (4)10 kW or higher
NG Replace air±fuel ratio (A/F) sensor.
OK

A19288
B17411
HA1A
E7HA2A
± DIAGNOSTICSENGINE
DI±91
285 Author: Date:
2005 SEQUOIA (RM1146U)
2 Check A/F relay.
PREPARATION:
Remove the A/F relay from the engine room R/B No.2.
CHECK:
Inspect the A/F relay.
OK:
Standard:
Terminal No.ConditionSpecified Condition
3 ± 5Always10 KW or higher
3 ± 5Apply B+ between
terminals 1 and 2Below 1 W
NG Replace A/F relay.
OK
3 Check voltage between terminals HA1A, HA2A 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 HA1A to the bank 1 sensor 1.

Connect terminal HA2A to the bank 2 sensor 1.
OK:
Standard:
Tester ConnectionSpecified Condition
HA1A (E7±2) ± Body ground9 V to 14 V
HA2A (E7±1) ± Body ground9 V to 14 V
OK Replace ECM (See page SF±80).
NG

A23659
Wire Harness Side:
HT
A38
Sensor 1A/F Sensor Connector
Front View
+B A39
B17415
E7ECM Connector
HA1A
HA2A
H24253
A/F Relay
Engine Room R/B No.2:
DI±92
± DIAGNOSTICSENGINE
286 Author: Date:
2005 SEQUOIA (RM1146U)
4 Check for open and short in harness and connector between ECM and A/F sen-
sor.
PREPARATION:
(a) Turn the ignition switch to OFF.
(b) Disconnect the A38 or A39 A/F sensor connector.
(c) Disconnect the E7 ECM connector.
CHECK:
Check the resistance.
OK:
Standard (Check for open):
Tester ConnectionsSpecified Conditions
HT (A38±1) ± HA1A (E7±2)
HT (A39±1) ± HA2A (E7±1)Below 1 W
Standard (Check for short):
Tester ConnectionsSpecified Conditions
HT (A38±1) or HA1A (E7±2) ± Body ground
HT (A39±1) or HA2A (E7±1) ± Body ground10 kW or higher
PREPARATION:
(a) Turn the ignition switch to OFF.
(b) Disconnect the A38 or A39 A/F sensor connector.
(c) Remove A/F relay from engine room R/B No.2.
CHECK:
Check the resistance.
OK:
Standard (Check for open):
Tester ConnectionsSpecified Conditions
+B (A38±2) ± A/F relay (3)
+B (A39±2) ± A/F relay (3)Below 1 W
Standard (Check for short):
Tester ConnectionsSpecified Conditions
+B (A38±2) or A/F relay (3) ± Body ground
+B (A39±2) or A/F relay (3) ± Body ground10 kW or higher
NG Repair or replace harness or connector.
OK
Check for intermittent problems
(See page DI±11).

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)

± 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

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

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).