Page 927 of 1897
A00477
Atmosphere
Cover
Exhaust GasPlatinum
Electrode
Solid Electrolyte
(Zirconia Element)
Platinum
Electrode
Heater
A/F Sensor Voltage
Air-Fuel Ratio
(V)
2.6 4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.4
12 13 14 15 16 17 18
Coating (Ceramic)
ECM Monitored
19
Housing
- DIAGNOSTICSENGINE
DI-43
199 Author: Date:
2001 AVALON (RM808U)
DTC P0125 Insufficient Coolant Temp. for Closed Loop
Fuel Control
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 A/F sensor has the characteristic that provides output voltage* approximately proportional to the exist-
ing air-fuel ratio. The A/F sensor output voltage* is used to provide feedback for the ECM to control the air-
fuel ratio.
By the A/F sensor output, the ECM can determine the deviation amount from the stoichiometric air-fuel ratio
and control the proper injection time immediately. If the A/F sensor is malfunctioning, ECM is unable to per-
form accurate air-fuel ratio control.
The A/F sensor is equipped with a heater which heats the zirconia element. The heater is controlled by the
ECM. When the intake air volume is low (the temp. of the exhaust gas is low), current flows to the heater
to heat the sensor for accurate oxygen concentration detection.
*: The voltage value changes at the inside of the ECM only.
DTC No.DTC Detecting ConditionTrouble Area
P0125
After engine is warmed up, A/F sensor output* does not
change when conditions (a), (b), (c) and (d) continue for at
least 1.5 min:
*: Output value changes at inside of the ECM only
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 40 - 100 km/h (25 - 62 mph)
(c) Throttle valve is not fully closed
(d) 140 sec. or more after starting engineOpen or short in A/F sensor (bank 1, 2 sensor 1) circuit
A/F sensor (bank 1, 2 sensor 1)
Air inducation system
Fuel pressure
Injector
Gas leakage on exhaust sytem
ECM
HINT:
After confirming DTC P0125, use the OBD II scan tool or TOYOTA hand-held tester to confirm voltage
output of the A/F sensor (bank 1, 2 sensor 1) from the CURRENT DATA.
The ECM controls the voltage of the AFR+, AFL+, AFR- and AFL- terminals of the ECM to the fixed
voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without the OBDII scan
tool or TOYOTA hand-held tester.
DI07M-14
Page 950 of 1897
A01674
Waveform of
A/F Sensor
Normal CatalystWaveform of Heated Oxygen
Sensor behind Catalyst
Abnormal Catalyst
- DIAGNOSTICSENGINE
DI-71
227 Author: Date:
2001 AVALON (RM808U)
DTC P0420 Catalyst System Efficiency Below Threshold
(Bank 1)
CIRCUIT DESCRIPTION
The ECM observes the waveform of the heated oxygen sensor located behind the catalyst to determine
whether the catalyst performance has deteriorated.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor located behind the catalyst
switches back and forth between rich and lean much more slowly.
When the waveform of the heated oxygen sensor located behind the catalyst alternates flutteringly between
rich and lean, it indicates that catalyst performance has deteriorated.
DTC No.DTC Detecting ConditionTrouble Area
P0420
After engine and catalyst are warmed up, and while vehicle is
driven within set vehicle and engine speed range, waveform of
heated oxygen sensor (bank 1 sensor 2) alternates flutteringly
between rich and lean (2 trip detection logic)Gas leakage on exhaust system
A/F sensor (bank 1, 2 sensor 1)
Heated oxygen sensor (bank 1 sensor 2)
Three-way catalytic converter
DI6T5-01
Page 952 of 1897
- DIAGNOSTICSENGINE
DI-73
229 Author: Date:
2001 AVALON (RM808U)
3 Check A/F sensor (bank 1, 2 sensor 1) (See page SF-79).
NG Repair or replace.
OK
4 Check heated oxygen sensor (bank 1 sensor 2) (See page SF-81).
NG Repair or replace.
OK
Replace three-way catalytic converter (See
page EC-15).
Page 1031 of 1897
- DIAGNOSTICSENGINE
DI-15
171 Author: Date:
P0171
(DI-53)System too Lean (Fuel Trim)
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leakage on exhaust system
Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
A/F sensor (bank 1, 2 sensor 1)
ECM
P0172
(DI-53)System too Rich (Fuel Trim)
Injector leak, blockage
Mass air flow meter
Engine coolant temp. sensor
Ignition system
Fuel pressure
Gas leakage on exhaust system
Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
A/F sensor (bank 1, 2 sensor 1)
ECM
P0174
(DI-53)System too Lean
(A/F Lean Malfunction)Same as DTC P0171
P0175
(DI-53)System too Rich
(A/F Rich Malfunction)Same as DTC P0172
P0300
(DI-58)Random/Multiple Cylinder Misfire
Detected
P0301
(DI-58)Cylinder 1 Misfire DetectedOpen or short in engine wire
Connector connection
Vh tiP0302
(DI-58)Cylinder 2 Misfire Detected
Vacuum hose connection
Ignition system
Injector
P0303
(DI-58)Cylinder 3 Misfire Detected
Injector
Fuel pressure
Mass air flow meter
*2
P0304
(DI-58)Cylinder 4 Misfire Detected
Mass air flow meter
Engine coolant temp. sensor
Compression pressure
Vl lP0305
(DI-58)Cylinder 5 Misfire Detected
Valve clearance
Valve timing
ECM
P0306
(DI-58)Cylinder 6 Misfire Detected
ECM
P0325
(DI-64)Knock Sensor 1 Circuit Malfunc-
tion (Bank 1)Open or short in knock sensor 1 circuit
Knock sensor 1 (looseness)
ECM
P0330
(DI-64)Knock Sensor 2 Circuit Malfunc-
tion (Bank 2)Open or short in knock sensor 2 circuit
Knock sensor 2 (looseness)
ECM
P0335
(DI-67)Crankshaft Position Sensor ºAº
Circuit Malfunction
Open or short in crankshaft position sensor circuit
Crankshaft position sensor
Crankshaft timing pulley
ECM
P0340
(DI-69)Camshaft Position Sensor Circuit
Malfunction
Open or short in camshaft position sensor circuit
Camshaft position sensor
Camshaft timing gear
ECM
P0420
(DI-71)Catalyst System Efficiency Be-
low Threshold (Bank 1)
Gas leakage on exhaust system
A/F sensor (bank 1, 2 sensor 1)
Heated oxygen sensor (bank 1 sensor 2)
Three-way catalytic converter
Page 1271 of 1897
EC01H-03
- EMISSION CONTROLEMISSION CONTROL SYSTEM
EC-1
1095 Author: Date:
2001 AVALON (RM808U)
EMISSION CONTROL SYSTEM
PURPOSE
The emission control systems are installed to reduce the amount of CO, HC and NOx exhausted from the
engine ((3) (4) and (5)), to prevent the atmospheric release of blow-by gas-containing HC (1) and evapo-
rated fuel containing HC being released from the fuel tank (2).
The function of each system is shown in these table.
SystemAbbreviationFunction
(1) Positive Crankcase Ventilation
(2) Evaporative Emission Control
(3) Warm Up Three-Way Catalytic Converter
(4) Three-Way Catalytic Converter
(5) Sequential Multiport Fuel injection*PCV
EVAP
WU-TWC
TWC
SFIReduces HC
Reduces evaporated HC
Reduces HC, CO and NOx
Reduces HC, CO and NOx
Injects a precisely timed, optimum amount of fuel for reduced
exhaust emissions
Remark: * For inspection and repair of the SFI system, refer to the SF section of this manual.
Page 1281 of 1897
EC04T-03
B07459
N´m (kgf´cm, ft´lbf) : Specified torque
Non-reusable part Gasket
44 (450, 33)
Damper Gasket
43 (440, 32)
TWC
Compression Spring
Center Exhaust PipeCompression Spring
43 (440, 32)
Heated Oxygen Sensor
(Bank 1 Sensor 2)
Heated Oxygen Sensor (Bank 1 Sensor 2)
HINT:
Before installing the heated oxygen sensor,
twist the sensor wire counterclockwise
3 and 1/2 turns.
After installing the heated oxygen sensor,
check that the sensor wire is not twisted,
if it is twisted, remove the heated oxygen
sensor and reinstall it.
- EMISSION CONTROLTHREE-W AY CATALYTIC CONVERTER (TWC)
SYSTEMEC-15
1109 Author: Date:
2001 AVALON (RM808U)
COMPONENTS
Page 1282 of 1897
EC04S-01
EC-14- EMISSION CONTROLTHREE-W AY CATALYTIC CONVERTER (TWC)
SYSTEM
1108 Author: Date:
2001 AVALON (RM808U)
THREE-W AY CATALYTIC CONVERTER (TWC) SYSTEM
ON-VEHICLE INSPECTION
1. INSPECT EXHAUST PIPE ASSEMBLY
(a) Check the connections for looseness or damage.
(b) Check the clamps for weakness, cracks or damage.
2. INSPECT TWC
Check for dents or damage.
If any part of the protector is damaged or dented to the extent that it contacts the TWC, repair or replace
it.
3. INSPECT TWC HEAT INSULATOR
(a) Check the heat insulator for damage.
(b) Check for adequate clearance between the catalytic converter and heat insulator.
Page 1283 of 1897
EC0BI-02
B07452
N´m (kgf´cm, ft´lbf) : Specified torque
Non-reusable part Gasket
62 (630, 46)
43 (440, 32)
Gasket
62 (630, 46)
33 (330, 24)
WU-TWC for Bank 1
Front Exhaust Pipe WU-TWC
Stay
Gasket
Compression Spring
EC-12- EMISSION CONTROLWARM UP THREE-W AY CATALYTIC CONVERTER
(WU-TWC) SYSTEM
1106 Author: Date:
2001 AVALON (RM808U)
COMPONENTS
