Toyota Sequoia (2005). Manual - part 71

A02961

V5
VVT Sensor (Bank 1)

ECM

1

2

R

G

Y

L

VVL+

VVL–

VVR+

E5

18

19

19

18

VVR–

1

2

E5

E4

E4

V6
VVT Sensor (Bank 2)

–

DIAGNOSTICS

ENGINE

DI–87

281

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT:

If DTC P0016 is displayed, check left bank VVT sensor.

If DTC P0018 is displayed, check right bank VVT sensor.

Read freeze frame data using hand–held tester or OBD II scan tool. Because freeze frame records
the engine conditions when the malfunction is detected. When troubleshooting, it is useful for deter-
mining whether the vehicle was running or stopped, the engine was warmed up or not, the air–fuel ratio
was lean or rich, etc. at the time of the malfunction.

1

Check valve timing (Check for loose and jumping teeth of timing belt) (See page

EM–16

).

NG

Adjust valve timing (Repair or replace timing
belt).

OK

Replace ECM (See page 

SF–80

).

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–88

–

DIAGNOSTICS

ENGINE

282

DTC

P0031

Oxygen (A/F) Sensor Heater Control Circuit
Low (Bank 1 Sensor 1)

DTC

P0032

Oxygen (A/F) Sensor Heater Control Circuit
High (Bank 1 Sensor 1)

DTC

P0051

Oxygen (A/F) Sensor Heater Control Circuit
Low (Bank 2 Sensor 1)

DTC

P0052

Oxygen (A/F) Sensor Heater Control Circuit
High (Bank 2 Sensor 1)

HINT:
Although each DTC title (DTC description) says ”oxygen sensor”, these DTCs are related to the ”A/F sensor”.

CIRCUIT DESCRIPTION

Refer to DTC P2195 on page 

DI–383

.

HINT:
The ECM provides a pulse width modulated control circuit to adjust current through the heater. The A/F sen-
sor heater circuit uses a relay on the B+ side of the circuit.

DTC No.

DTC Detection Condition

Trouble Area

P0031
P0051

Heated current is 0.8 A or less when heater operates 

(1 trip detection logic)

Open or short in heater circuit of A/F sensor

A/F sensor heater

P0032
P0052

When the heater operates, heated current exceeds 19.7 A 

(1 trip detection logic)

A/F sensor heater

A/F sensor heater relay

ECM

DIDFP–01

–

DIAGNOSTICS

ENGINE

DI–89

283

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

P0031

A/F sensor heater (Bank 1) range check (Low

current)

R l t d DTC

P0032

A/F sensor heater (Bank 1) range check (High

current)

Related DTCs

P0051

A/F sensor heater (Bank 2) range check (Low

current)

P0052

A/F sensor heater (Bank 2) range check (High

current)

R

i d

/

t

Main sensors/components

A/F sensor heater

Required sensors/components

Related sensors/components

–

Frequency of operation

Continuous

Duration

10 sec.

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

P0031, P0051 (Low current):

Battery voltage

10.5 V

–

A/F sensor heater duty ratio

50%

–

Time after engine start

10 sec.

–

B17396

HT

+B

AF–

AF+

Sensor 1

A/F Sensor

Component Side:

Front View

DI–90

–

DIAGNOSTICS

ENGINE

284

P0032, P0052 (High current):

Time after engine start

10 sec.

–

TYPICAL MALFUNCTION THRESHOLDS

Detection Criteria

Threshold

P0031, P0051 (Low current):

A/F sensor heater current

Less than 0.8 A

P0032, P0052 (High current):

A/F sensor heater current

More than 10 A

COMPONENT OPERATING RANGE

Parameter

Standard Value

A/F sensor heater current

1.8 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 Connection

Specified Condition

HT (1) – +B (2)

1.8 

Ω

 to 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