2001 TOYOTA SEQUOIA O2 sensor

± DIAGNOSTICSENGINE
DI±403
597 Author: Date:
2005 SEQUOIA (RM1146U)
CIRCUIT DESCRIPTION
Refer to DTC P2195 on page DI±383.
DTC No.DTC Detection ConditionsTrouble Areas
P2238
P2241

Case 1:
Condition (a) or (b) continues for 5.0 seconds or more
(1 trip detection logic):
(a) AF+ voltage 0.5 V or less
(b) (AF+) ± (AF±) = 0.1 V or less

Case 2:
A/F sensor admittance: Less than 0.022 1/W
(1 trip detection logic)

Open or short in A/F sensor (sensor 1) circuit

A/F sensor (sensor 1)

A/F sensor heater

EFI relay

A/F sensor heater and relay circuits

ECM
P2239
P2242AF+ voltage more than 4.5 V for 5.0 seconds or more
(1 trip detection logic)

Open or short in A/F sensor (sensor 1) circuit

A/F sensor (sensor 1)

A/F sensor heater

EFI relay

A/F sensor heater and relay circuits

ECM
P2252
P2255AF± voltage 0.5 V or less for 5.0 seconds or more
(1 trip detection logic)

Open or short in A/F sensor (sensor 1) circuit

A/F sensor (sensor 1)

A/F sensor heater

EFI relay

A/F sensor heater and relay circuits

ECM
P2253
P2256AF± voltage more than 4.5 V for 5.0 seconds or more
(1 trip detection logic)

Open or short in A/F sensor (sensor 1) circuit

A/F sensor (sensor 1)

A/F sensor heater

EFI relay

A/F sensor heater and relay circuits

ECM
MONITOR DESCRIPTION
The Air±Fuel Ratio (A/F) sensor varies its output voltage in proportion to the air±fuel ratio. If the A/F sensor
impedance (alternating current resistance) or voltage output deviates greatly from the standard range, the
ECM determines that there is an open or short malfunction in the A/F sensor circuit.

DI±404
± DIAGNOSTICSENGINE
598 Author: Date:
2005 SEQUOIA (RM1146U)
MONITOR STRATEGY
A/F sensor (Bank 1) open circuit between AF+
and AF±
P2238A/F sensor (Bank 1) short circuit between AF+
and AF±
A/F sensor (Bank 1) short circuit between AF+
and GND
P2239A/F sensor (Bank 1) short circuit between AF+
and +B
A/F sensor (Bank 2) open circuit between AF+
and AF±
RltdDTC
P2241A/F sensor (Bank 2) short circuit between AF+
and AF±
Related DTCsA/F sensor (Bank 2) short circuit between AF+
and GND
P2242A/F sensor (Bank 2) short circuit between AF+
and +B
P2252A/F sensor (Bank 1) short circuit between AF±
and GND
P2253A/F sensor (Bank 1) short circuit between AF±
and +B
P2255A/F sensor (Bank 2) short circuit between AF±
and GND
P2256A/F sensor (Bank 2) short circuit between AF±
and +B
Required sensors/componentsA/F sensor
Frequency of operationOnce per driving cycle
Duration10 sec.: A/F sensor open circuit between AF+ and AF±
5 sec.: Others
MIL operationImmediate
Sequence of operationNone
TYPICAL ENABLING CONDITIONS
ItSpecificationItemMinimumMaximum
The monitor will run whenever these
DTCs are not presentSee page DI±18
P2238, P2241 (A/F sensor open circuit between AF+ and AF±):
Duration while all of following conditions
met20 sec.±
AF+ terminal voltage0.5 to 4.5 V
AF± terminal voltage0.5 to 4.5 V
Difference between AF+ terminal and AF±
terminal voltage0.1 to 0.8 V
ECT20°C (68°F)±
EngineRunning
Time after engine start20 sec.±
Fuel±cutOFF
A/F sensor heater duty cycle0%±

± DIAGNOSTICSENGINE
DI±405
599 Author: Date:
2005 SEQUOIA (RM1146U) Time after A/F sensor heating
20 sec.±
Battery voltage10.5 V±
Ignition switchON
Others:
Battery voltage10.5 V±
Ignition switchON
TYPICAL MALFUNCTION THRESHOLDS
Detection CriteriaThreshold
P2238, P2241 (A/F sensor open circuit between AF+ and AF±):
A/F sensor admittanceBellow 0.022 1/ohm
P2238, P2241 (A/F sensor short circuit between AF+ and GND):
A/F+ terminal voltage0.5 V or less
P2238, P2241 (A/F sensor short circuit between AF+ and AF±):
Difference between A/F+ terminal and AF± terminal voltage0.1 V or less
P2239, P2242 (A/F sensor short circuit between AF+ and +B):
A/F+ terminal voltageMore than 4.5 V
P2252, P2255 (A/F sensor short circuit between AF± and GND):
A/F± terminal voltage0.5 V or less
P2253, P225+ (A/F sensor short circuit between AF± and +B):
A/F± terminal voltageMore than 4.5 V
WIRING DIAGRAM
Refer to DTC P2195 on page DI±383.
INSPECTION PROCEDURE
HINT:
Hand±held tester only:
Malfunctioning areas can be identified by performing the A/F CONTROL function provided in the ACTIVE
TEST. The A/F CONTROL function can help to determine whether the Air±Fuel Ratio (A/F) sensor, Heated
Oxygen (HO2) sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the A/F CONTROL operation using a hand±held tester.
(1) Connect a hand±held tester to the DLC3.
(2) Start the engine and turn the tester ON.
(3) Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
(4) On the tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE
TEST / A/F CONTROL.
(5) Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT
or LEFT button to change the fuel injection volume).
(6) Monitor the voltage outputs of the A/F and HO2 sensors (AFS B1S1 (AFS B2S1) and OS2 B1S2
(O2S B2S2)) displayed on the tester.
HINT:

The A/F CONTROL operation lowers the fuel injection volume by 12.5 % or increases the injection
volume by 25 %.

Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

+25 %
±12.5 %
More than 3.35 V
Less than 3.0 V
1
A/F Sensor (Sensor 1)
Output Voltage
Injection volume
Output voltage
HO2 Sensor (Sensor 2)
Output VoltageMain Suspected
Trouble Areas
OK
+25 %
±12.5 %
More than 3.35 V
Less than 3.0V
Injection volume
Output voltage
+25 %
±12.5 %
More than 0.55 V
Less than 0.4V
Injection volume
Output voltage
A/F sensor+25 %
±12.5 %
More than 0.55 V
Less than 0.4V
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
NG OK
OK
OK
Almost
no reaction
'
Almost
no reaction Almost
no reaction
Almost
no reaction
Case
2
3
4
A/F sensor circuit A/F sensor heater
HO2 sensor
HO2 sensor circuit HO2 sensor heater
(Air±fuel ratio extremely
lean or rich)Injector
Gas leakage from
exhaust system Fuel pressure
DI±406
± DIAGNOSTICSENGINE
600 Author: Date:
2005 SEQUOIA (RM1146U)
Standard:
Tester Display
(Sensor)Injection VolumesStatusVoltages
AFS B1S1 (AFS B2S1)
(A/F)+25 %RichLess than 3.0
AFS B1S1 (AFS B2S1)
(A/F)±12.5 %LeanMore than 3.35
O2S B1S2 (O2S B2S2)
(HO2)+25 %RichMore than 0.55
O2S B1S2 (O2S B2S2)
(HO2)±12.5 %LeanLess than 0.4
NOTICE:
The Air±Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2)
sensor has a maximum output delay of approximately 20 seconds.

Following the A/F CONTROL procedure enables technicians to check and graph the voltage outputs
of both the A/F and HO2 sensors.

To display the graph, select the following menu items on the tester: DIAGNOSIS / ENHANCED OBD
II / ACTIVE TEST / A/F CONTROL / USER DATA / AFS B1S1 and O2S B1S2, and press the YES but-
ton and then the ENTER button followed by the F4 button.

B17396
HT +B
AF± AF+ Sensor 1A/F Sensor Component Side:
Front View
A19288
± DIAGNOSTICSENGINE
DI±407
601 Author: Date:
2005 SEQUOIA (RM1146U)
HINT:
Read freeze frame data using a hand±held tester. Freeze frame data record the engine condition when mal-
functions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was mov-
ing 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:
Tester ConnectionSpecified Condition
HT (1) ± +B (2)Between 1.8 W and 3.4 W at 20C (68F)
HT (1) ± AF± (4)10 kW or higher
NG Replace air±fuel ratio (A/F) sensor.
OK
2 Check A/F relay.
PREPARATION:
Remove the A/F relay from the engine room J/B.
CHECK:
Inspect the A/F relay.
OK:
Terminal No.ConditionSpecified Condition
1 ± 2ConstantContinuity
UsuallyNo Continuity
3 ± 5Apply B+ between
terminals 1 and 2Continuity
NG Replace EFI relay.
OK

A23659
Wire Harness Side:
HT
A38
Sensor 1A/F Sensor Connector
AF+
Front ViewAF±
+B A39
B17415A55007
E7ECM Connector
HA1A
A1A+
A1A±
A2A+
A2A±HA2A
A23512
Reference (Bank 1 Sensor 1 System Drawing):
A/F Sensor A/F Relay
Heater
Sensor
A1A+ HA1A
Duty
Control ECM
From
Battery
A/F Heater
Fuse
A1A±
To EFI Relay DI±408
± DIAGNOSTICSENGINE
602 Author: Date:
2005 SEQUOIA (RM1146U)
3 Check for open and short in harness and connector between ECM and A/F sen-
sor.
PREPARATION:
(a) Disconnect the A38 or A39 A/F sensor connector.
(b) Turn the ignition switch to ON.
CHECK:
(a) Measure the voltage between the +B terminal of the A/F
sensor connector and body ground.
OK:
Standard:
Tester ConnectionsSpecified Conditions
+B (2) ± Body groundBetween 9 V and 14 V
PREPARATION:
(a) Turn the ignition switch to OFF.
(b) Disconnect the E7 ECM connector.
CHECK:
(a) 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
AF+ (A38±3) ± A1A+ (E7±22)
AF+ (A39±3) ± A2A+ (E7±23)Below 1 W
AF± (A38±4) ± A1A± (E7±30)
AF± (A39±4) ± A2A± (E7±31)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
AF+ (A38±3) or A1A+ (E7±22) ± Body ground
AF+ (A39±3) or A2A+ (E7±23) ± Body ground10 kW or higher
AF± (A38±4) or A1A± (E7±30) ± Body ground
AF± (A39±4) or A2A± (E7±31) ± Body ground10 kW or higher

A23480
Fuel Tank Canister
Vacuum Pump: OFF Pressure Sensor 0.02 Inch Orifice
Pump Module
Operation A: Atmospheric Pressure Measurement
Vent Valve: OFF (vent)
Operation D: Purge VSV monitor Operation B: 0.02 Inch Leak Pressure Measurement
Negative
Pressure Atmospheric
Pressure
Operation C: EVAP Leak Check
Air Filter
Purge VSV: OFFOFF (vent)
ON
OFF
OFF
ON
ON (closed)ON
ON
ON (closed)
± DIAGNOSTICSENGINE
DI±411
605 Author: Date:
2005 SEQUOIA (RM1146U)
MONITOR DESCRIPTION
5 hours* after the ignition switch is turned OFF, the electric vacuum pump creates negative pressure (vacu-
um) in the EVAP (Evaporative Emission) system. The ECM monitors for leaks and actuator malfunctions
based on the EVAP pressure.
HINT:
*: If the engine coolant temperature is not below 35C (95F) 5 hours after the ignition switch is turned off,
the monitor check starts 2 hours later. If it is still not below 35C (95F) 7 hours after the ignition switch is
turned off, the monitor check starts 2.5 hours later.
SequenceOperationsDescriptionsDuration
±ECM activationActivated by soak timer, 5 hours (7 or 9.5 hours) after ignition switch turned to OFF.±
AAtmospheric pressure
measurement
Vent valve turned OFF (vent) and EVAP system pressure measured by ECM in order to
register atmospheric pressure.
If EVAP pressure is not between 70 kPa and 110 kPa (525 mmHg and 825 mmHg), ECM
cancels EVAP system monitor.
10 seconds
B
First 0.02 inch leak
pressure measure-
mentIn order to determine 0.02 inch leak pressure standard, vacuum pump creates negative pres-
sure (vacuum) through 0.02 inch orifice and them ECM checks if vacuum pump and vent
valve operate normally.
60 seconds
CEVAP system pres-
sure measurement
Vent valve turned ON (closed) to shut EVAP system.
Negative pressure (vacuum) created in EVAP system, and EVAP system pressure then
measured.
Write down the measured value as it will be used in the leak check.
If EVAP pressure does not stabilize within 15 minutes, ECM cancels EVAP system monitor.
15 minutes*
DPurge VSV monitorPurge VSV opened and then EVAP system pressure measured by ECM.
Large increase indicates normal.10 seconds
E
Second 0.02 inch leak
pressure measure-
mentLeak check is performed after second 0.02 inch leak pressure standard is measured.
If stabilized system pressure higher than second 0.02 inch leak pressure standard, ECM
determines that EVAP system leaking.
60 seconds
FFinal checkAtmospheric pressure measured and then monitoring result recorded by ECM.±
* If only a small amount of fuel is in the fuel tank, it takes longer for the EVAP pressure to stabilize.

A23664
Purge VSV
Vent Valve
Vacuum Pump
EVAP Pressure
Positive
Leak Pressure
sec NegativeONON
Sequence
TimeA
10
sec60
Within 15 minutesON
First 0.02 inch
BCD
OK Malfunction
ON: Open
OFF: Closed
OFF: Vent ON: Closed
10
Standard
sec60
E
sec
EVAP Pressure when Vacuum Pump Stuck OFF: DI±412
± DIAGNOSTICSENGINE
606 Author: Date:
2005 SEQUOIA (RM1146U)
(a) P2401: Vacuum pump stuck OFF
In operation B, the vacuum pump creates negative pressure (a vacuum) through the 0.02 inch orifice. The
EVAP (Evaporative Emission) system pressure is then measured by the ECM, using the pressure sensor,
to determine the 0.02 inch leak pressure standard. If the pressure is higher than ±1.06 kPa (±7.95 mmHg)*,
or lower than ±4.85 kPa (±36.38 mmHg)*, the ECM interprets this as the vacuum pump being stuck OFF
(not operating). The ECM illuminates the MIL and sets the DTC (2 trip detection logic).
*: The thresholds vary according to the atmospheric pressure measured in operation A. The values de-
scribed above are based on an atmospheric pressure of 100 kPa (750.1 mmHg): absolute pressure.