Toyota Sequoia (2005). Manual - part 72

A19288

B17411

HA1A

E7

HA2A

–

DIAGNOSTICS

ENGINE

DI–91

285

2

Check A/F relay.

PREPARATION:
Remove the A/F relay from the engine room R/B No.2.
CHECK:
Inspect the A/F relay.
OK:

Standard:

Terminal No.

Condition

Specified Condition

3 – 5

Always

10 K

Ω

 or higher

3 – 5

Apply B+ between 

terminals 1 and 2

Below 1  

Ω

NG

Replace A/F relay.

OK

3

Check voltage between terminals HA1A, HA2A of ECM connectors and body
ground.

PREPARATION:
Turn the ignition switch ON.
CHECK:
Measure the voltage between terminals of the ECM connectors
and body ground.
HINT:

Connect terminal HA1A to the bank 1 sensor 1.

Connect terminal HA2A to the bank 2 sensor 1.

OK:

Standard:

Tester Connection

Specified Condition

HA1A (E7–2) – Body ground

9 V to 14 V

HA2A (E7–1) – Body ground

9 V to 14 V

OK

Replace ECM (See page 

SF–80

).

NG

A23659

Wire Harness Side:

HT

A38

Sensor 1

A/F Sensor Connector

Front View

+B

A39

B17415

E7 ECM Connector

HA1A

HA2A

H24253

A/F Relay

Engine Room R/B No.2:

DI–92

–

DIAGNOSTICS

ENGINE

286

4

Check for open and short in harness and connector between ECM and A/F sen-
sor.

PREPARATION:
(a)

Turn the ignition switch to OFF.

(b)

Disconnect the A38 or A39 A/F sensor connector.

(c)

Disconnect the E7 ECM connector.

CHECK:
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

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

PREPARATION:
(a)

Turn the ignition switch to OFF.

(b)

Disconnect the A38 or A39 A/F sensor connector.

(c)

Remove A/F relay from engine room R/B No.2.

CHECK:
Check the resistance.
OK:

Standard (Check for open):

Tester Connections

Specified Conditions

+B (A38–2) – A/F relay (3)

+B (A39–2) – A/F relay (3)

Below 1 

Ω

Standard (Check for short):

Tester Connections

Specified Conditions

+B (A38–2) or A/F relay (3) – Body ground
+B (A39–2) or A/F relay (3) – Body ground

10 k

Ω

 or higher

NG

Repair or replace harness or connector.

OK

Check for intermittent problems 
(See page 

DI–11

).

–

DIAGNOSTICS

ENGINE

DI–93

287

DTC

P0037

Oxygen Sensor Heater Control Circuit Low
(Bank 1 Sensor 2)

DTC

P0038

Oxygen Sensor Heater Control Circuit High
(Bank 1 Sensor 2)

DTC

P0057

Oxygen Sensor Heater Control Circuit Low
(Bank 2 Sensor 2)

DTC

P0058

Oxygen Sensor Heater Control Circuit High
(Bank 2 Sensor 2)

DID83–01

B17386

Housing

Solid Electrolyte
(Zirconia Element)

Platinum Electrode

Heater

Coating (Ceramic)

Exhaust Gas

Cover

Ideal Air–Fuel Mixture

Output V

oltage

Richer – Air Fuel Ratio – Leaner

Atmospheric Air

A21040

Reference (Bank 1 Sensor 1 System Drawing) :

ECM

EFI Relay

EFI Fuse No. 1

From 
Battery

Ground

OX1A

MREL

HT1A

Duty 
Control

Heater

Sensor

Heated Oxygen Sensor

EFI Fuse No. 2

E2

DI–94

–

DIAGNOSTICS

ENGINE

288

CIRCUIT DESCRIPTION

To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three–way cata-
lytic converter is used, but for the most efficient use of the three–way catalytic converter, the air–fuel ratio
must be precisely controlled so that it is always close to the stoichiometric air–fuel ratio.
The heated oxygen sensor has the characteristic which its output voltage changes suddenly in the vicinity
of the stoichiometric air–fuel ratio. This characteristic is used to detect the oxygen concentration in the ex-
haust gas and provide the ECM with feedback to control the air–fuel ratio.
When the air–fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the heated
oxygen sensor informs the ECM of the LEAN condition (low voltage, i.e. less than 0.45 V).
When the air–fuel ratio is RICHER than the stoichiometric air–fuel ratio, the oxygen concentration in the ex-
haust gas is reduced and the heated oxygen sensor informs the ECM of the RICH condition (high voltage,
i.e. more than 0.45 V). The ECM judges by the voltage output from the heated oxygen sensor whether the
air–fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the
heated oxygen sensor causes output of abnormal voltage, this disables the ECM for performing an accurate
air–fuel ratio control. The heated oxygen sensors include a heater which heats the zirconia element. The
heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is
low) current flows to the heater to heat the sensor for accurate oxygen concentration detection.

HINT:
The ECM provides a pulse width modulated control circuit to adjust current through the heater. The heated
oxygen sensor heater circuit uses a relay on the B+ side of the circuit.