Toyota Sequoia (2005). Manual - part 73

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DIAGNOSTICS

ENGINE

DI–95

289

DTC No.

DTC Detecting Condition

Trouble Area

P0037

Heater current is 0.25 A or less when the heater operates with

Open in heater circuit of heated oxygen sensor

Heated oxygen sensor heater

P0037

P0057

Heater current is 0.25 A or less when the heater o erates with

more than 10.5 V positive battery voltage

Heated oxygen sensor heater

EFI relay

ECM

P0038

P0058

When heater operates, heater current exceeds 2.0 A

Short in heater circuit of heated oxygen sensor

Heated oxygen sensor heater

EFI relay

ECM

HINT:

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

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

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

Sensor 2 refers to the sensor farther away from the engine assembly.

MONITOR DESCRIPTION

The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect oxygen
concentration in the exhaust. If the zirconia element is at the proper temperature and difference of the oxy-
gen concentration between the inside and outside surface of sensor is large, the zirconia element will gener-
ate voltage signals. In order to increase the oxygen concentration detecting capacity in the zirconia element,
the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor. When
current in the sensor is out of the standard operating range, the ECM interprets this as a fault in the heated
oxygen sensor and sets a DTC.
Example:
The ECM will set a high current DTC if the current in the sensor is more than 2.0 A when the heater is OFF.
Similarly, the ECM will set a low current DTC if the current is less than 0.3 A when the heater is ON.

MONITOR STRATEGY

P0037

Rear HO2S heater (Bank 1) range check (Low

Current)

R l t d DTC

P0038

Rear HO2S heater (Bank 1) range check (High

Current)

Related DTCs

P0057

Rear HO2S heater (Bank 2) range check (Low

Current)

P0058

Rear HO2S heater (Bank 2) range check (High

Current)

R

i d

/

t

Main sensors/components

HO2S heater

Required sensors/components

Related sensors/components

Vehicle speed sensor (VSS)

Frequency of operation

Continuous

Duration

0.3 sec.

MIL operation

Immediate

Sequence of operation

None

DI–96

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DIAGNOSTICS

ENGINE

290

TYPICAL ENABLING CONDITIONS

It

Specification

Item

Minimum

Maximum

The monitor will run whenever these
DTCs are not present

See page 

DI–18

P0037, P0057 (Low current):

Battery voltage

10.5 V

–

All heater is turned OFF and intrusive
heating is operated when the following
conditions are met

Condition (a) and (b)

(a) Heater

ON

(b) Heater current

–

0.3 A

P0038, P0058 (High current):

Case 1:

Battery voltage

10.5 V

–

Engine

Running

Starter

OFF

Intrusive heating

Not operating

Case 2:

Battery voltage

10.5 V

–

All heater is turned OFF and intrusive
heating is operated when the following
conditions are met

Condition (a) and (b)

(a) Heater

ON

(b) Heater current

2 A

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TYPICAL MALFUNCTION THRESHOLDS

Detection Criteria

Threshold

P0037, P0057 (Low current):

HO2S heater current during intrusive heating

Less than 0.3 A (when battery voltage is 10.5 V or more)

P0038, P0058 (High current):

Case 1:

HO2S heater current

2 A or more

Case 2:

HO2S heater current during intrusive heating

More than 2 A

COMPONENT OPERATING RANGE

Parameter

Standard Value

HO2S heater current

0.4 to 1 A (at idle, warmed–up engine and +B: 11 to 14 V)

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DIAGNOSTICS

ENGINE

DI–97

291

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

TLT

CID

Unit Conversion

Description of Test Data

Description of Test Limit

1

$02

Multiply by 0.000076

(A)

Maximum HO2S heater current

(Bank 1 Sensor 2)

Malfunction threshold for HO2S heater

1

$20

Multiply by 0.000076

(A)

Maximum HO2S heater current

(Bank 2 Sensor 2)

Malfunction threshold for HO2S heater

A23550

Battery

2F

ECM

OX1B

HT2B

OX2B

33

Y

A

G–R

3

2

E

R

B–W

ED

W–B

5

4

5

1

22

J2

IG4

HTR2

NTL2

OXR2

E8

F10
Fusible Link
Block

G–R

EC

2D

1

1

2H

6

2A

2

EFI Relay

EFI No. 1

EFI No. 2

J/C

IA4

G–R

HT1B

8

5

18

E8

E7

E7

E4

G–R

G–R

14

IA4

B–W

OXL2

1

4

A

G–R

Engine Room J/B

J42
J/C

A

B

J5
J/C

W–R

E8

E6

G–W

BR

BR

H4 Heated Oxygen Sensor
(Bank 2 Sensor 2)

H2 Heated Oxygen Sensor
(Bank 1 Sensor 2)

J16

28

1

(Shielded)

B

E

B

EB

J42
J/C

G–W

G–W

E1

B

G

J/C

E1

+B

+B

E1

E2

MREL

(Shielded)

C

C

C

BR

DI–98

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DIAGNOSTICS

ENGINE

292

WIRING DIAGRAM