Toyota Sequoia (2005). Manual - part 152

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DIAGNOSTICS

ENGINE

DI–403

597

CIRCUIT DESCRIPTION

Refer to DTC P2195 on page 

DI–383

.

DTC No.

DTC Detection Conditions

Trouble 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/

Ω 

(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
P2242

AF+ 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
P2255

AF– 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
P2256

AF– 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

–

DIAGNOSTICS

ENGINE

598

MONITOR STRATEGY

A/F sensor (Bank 1) open circuit between AF+
and AF–

P2238

A/F sensor (Bank 1) short circuit between AF+
and AF–

A/F sensor (Bank 1) short circuit between AF+
and GND

P2239

A/F sensor (Bank 1) short circuit between AF+
and +B

A/F sensor (Bank 2) open circuit between AF+
and AF–

R l t d DTC

P2241

A/F sensor (Bank 2) short circuit between AF+
and AF–

Related DTCs

A/F sensor (Bank 2) short circuit between AF+
and GND

P2242

A/F sensor (Bank 2) short circuit between AF+
and +B

P2252

A/F sensor (Bank 1) short circuit between AF–
and GND

P2253

A/F sensor (Bank 1) short circuit between AF–
and +B

P2255

A/F sensor (Bank 2) short circuit between AF–
and GND

P2256

A/F sensor (Bank 2) short circuit between AF–
and +B

Required sensors/components

A/F sensor

Frequency of operation

Once per driving cycle

Duration

10 sec.: A/F sensor open circuit between AF+ and AF–
5 sec.: Others

MIL operation

Immediate

Sequence of operation

None

TYPICAL ENABLING CONDITIONS

It

Specification

Item

Minimum

Maximum

The monitor will run whenever these

DTCs are not present

See page 

DI–18

P2238, P2241 (A/F sensor open circuit between AF+ and AF–):

Duration while all of following conditions
met

20 sec.

–

AF+ terminal voltage

0.5 to 4.5 V

AF– terminal voltage

0.5 to 4.5 V

Difference between AF+ terminal and AF–
terminal voltage

0.1 to 0.8 V

ECT

20

°

C (68

°

F)

–

Engine

Running

Time after engine start

20 sec.

–

Fuel–cut

OFF

A/F sensor heater duty cycle

0%

–

–

DIAGNOSTICS

ENGINE

DI–405

599

Time after A/F sensor heating

20 sec.

–

Battery voltage

10.5 V

–

Ignition switch

ON

Others:

Battery voltage

10.5 V

–

Ignition switch

ON

TYPICAL MALFUNCTION THRESHOLDS

Detection Criteria

Threshold

P2238, P2241 (A/F sensor open circuit between AF+ and AF–):

A/F sensor admittance

Bellow 0.022 1/ohm

P2238, P2241 (A/F sensor short circuit between AF+ and GND):

A/F+ terminal voltage

0.5 V or less

P2238, P2241 (A/F sensor short circuit between AF+ and AF–):

Difference between A/F+ terminal and AF– terminal voltage

0.1 V or less

P2239, P2242 (A/F sensor short circuit between AF+ and +B):

A/F+ terminal voltage

More than 4.5 V

P2252, P2255 (A/F sensor short circuit between AF– and GND):

A/F– terminal voltage

0.5 V or less

P2253, P225+ (A/F sensor short circuit between AF– and +B):

A/F– terminal voltage

More 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 Voltage

Main 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

–

DIAGNOSTICS

ENGINE

600

Standard:

Tester Display

(Sensor)

Injection Volumes

Status

Voltages

AFS B1S1 (AFS B2S1)

(A/F)

+25 %

Rich

Less than 3.0

AFS B1S1 (AFS B2S1)

(A/F)

–12.5 %

Lean

More than 3.35

O2S B1S2 (O2S B2S2)

(HO2)

+25 %

Rich

More than 0.55

O2S B1S2 (O2S B2S2)

(HO2)

–12.5 %

Lean

Less 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.