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
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
–
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.
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