Toyota Sequoia (2005). Manual - part 165

+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

–

DIAGNOSTICS

ENGINE

DI–455

649

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.

HINT:

DTC P2A00 may be also set, when the air–fuel ratio is stuck rich or lean.

A low A/F sensor voltage could be caused by a rich air–fuel mixture. Check for conditions that would
cause the engine to run rich.

A high A/F sensor voltage could be caused by a lean air–fuel mixture. Check for conditions that would
cause the engine to run lean.

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.

B17396

HT

+B

AF–

AF+

Sensor 1

A/F Sensor

Component Side:

Front View

DI–456

–

DIAGNOSTICS

ENGINE

650

1

Check any other DTCs output (in addition to DTC P2A00 or P2A03).

PREPARATION:
(a)

Connect a hand–held tester to the DLC3.

(b)

Turn the ignition switch to ON and turn the tester ON.

(c)

Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.

CHECK:
(a)

Read DTCs.
Result:

Display (DTC Output)

Proceed To

P2A00 and/or P2A03

A

P2A00 and/or P2A03 and other DTCs

B

HINT:
If any DTCs other than P2A00 and/or P2A03 are output, troubleshoot those DTCs first.

B

Go to DTC chart (See page 

DI–58

).

A

2

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 Connection

Specified Condition

HT (1) – +B (2)

Between 1.8 

Ω

 and 3.4 

Ω

 at 20



C (68



F)

HT (1) – AF– (4)

10 k

Ω

 or higher

NG

Replace air–fuel ratio (A/F) sensor.

OK

A23659

Wire Harness Side:

HT

A38

Sensor 1

A/F Sensor Connector

AF+

Front View

AF–

+B

A39

B17415

A55007

E7

ECM 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

–

DIAGNOSTICS

ENGINE

DI–457

651

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 Connections

Specified Conditions

+B (2) – Body ground

Between 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 Connections

Specified Conditions

HT (A38–1) – HA1A (E7–2)

HT (A39–1) – HA2A (E7–1)

Below 1 

Ω

AF+ (A38–3) – A1A+ (E7–22)

AF+ (A39–3) – A2A+ (E7–23)

Below 1 

Ω

AF– (A38–4) – A1A– (E7–30)

AF– (A39–4) – A2A– (E7–31)

Below 1 

Ω

Standard (Check for short):

Tester Connections

Specified Conditions

HT (A38–1) or HA1A (E7–2) – Body ground
HT (A39–1) or HA2A (E7–1) – Body ground

10 k

Ω

 or higher

AF+ (A38–3) or A1A+ (E7–22) – Body ground
AF+ (A39–3) or A2A+ (E7–23) – Body ground

10 k

Ω

 or higher

AF– (A38–4) or A1A– (E7–30) – Body ground
AF– (A39–4) or A2A– (E7–31) – Body ground

10 k

Ω

 or higher

DI–458

–

DIAGNOSTICS

ENGINE

652

NG

Replace or replace harness or connector.

OK

4

Perform confirmation driving pattern.

NEXT

5

Check whether DTC output recurs (DTC P2A00 or P2A03)

CHECK:
(a)

On the hand–held tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC
INFO / PENDING CODES.

(b)

Read DTCs.

RESULT:

Display (DTC Output)

Proceed To

P2A00 or P2A03

A

No output

B

B

Check for intermittent problems 
(See page 

DI–11

).

A

6

Replace air fuel ratio sensor.

NEXT

7

Perform confirmation driving pattern.

NEXT