1995 TOYOTA SUPRA catalytic converter

Wire Harness and Connector
The SRS wire harness is integrated with the cowl wire har-
ness assembly and floor wire harness assembly. The wires
for the SRS wire harness are encased in a yellow corrugated
tube. All the connectors for the system are also a standard
yellow color. If the SRS wire harness becomes disconnected
or the connector becomes broken due to an accident, etc.,
repair or replace it as shown on page RS±36.
FOR VEHICLES EQUIPPED WITH A CATALYTIC CONVERTER
CAUTION: If large amounts of unburned gasoline flow into the converter, it may overheat and create a fire
hazard. To prevent this, observe the following precautions and explain them to your customer.
1. Use only unleaded gasoline.
2. Avoid prolonged idling.
Avoid running the engine at idle speed for more than 20 minutes.
3. Avoid spark jump test.
(a) Perform spark jump test only when absolutely necessary. Perform this test as rapidly as possible.
(b) While testing, never race the engine.
4. Avoid prolonged engine compression measurement.
Engine compression tests must be done as rapidly as possible.
5. Do not run engine when fuel tank is nearly empty.
This may cause the engine to misfire and create an extra load on the converter.
6. Avoid coasting with ignition turned off and prolonged braking.
7. Do not dispose of used catalyst along with parts contaminated with gasoline or oil.
± INTRODUCTIONPRECAUTIONIN±15

 IAC Idle Air Control Idle Speed Control (ISC)
IATIntake Air TemperatureIntake or Inlet Air Temperature ICM Ignition Control Module ± IFI Indirect Fuel Injection Indirect Injection IFS Inertia Fuel±Shutoff ±
 ISC Idle Speed Control ±
 KS Knock Sensor Knock Sensor
 MAF Mass Air Flow Air Flow Meter
 MAP Manifold Absolute Pressure Manifold Pressure
Intake Vacuum
 
 
 
MC
 
 
 
Mixture Control
 
 
 
Electric Bleed Air Control Valve (EBCV)
Mixture Control Valve (MCV)
Electric Air Control Valve (EACV)
 MDP Manifold Differential Pressure ±
 MFI Multiport Fuel Injection Electronic Fuel Injection (EFI)
MILMalfunction Indicator LampCheck Engine Light MST Manifold Surface Temperature ± MVZ Manifold Vacuum Zone ± NVRAM Non±Volatile Random Access Memory ±
 O2S Oxygen Sensor Oxygen Sensor, O2 Sensor (O2S)
 OBD On±Board Diagnostic On±Board Diagnostic (OBD)
 OC Oxidation Catalytic Converter Oxidation Catalyst Converter (OC), CCo
OPOpen LoopOpen Loop PAIR Pulsed Secondary Air Injection Air Suction (AS) PCM Powertrain Control Module ± PNP Park/Neutral Position ±
 PROM Programmable Read Only Memory ±
 PSP Power Steering Pressure ±
 
 
PTOX 
 
Periodic Trap Oxidizer 
 
Diesel Particulate Filter (DPF)
Diesel Particulate Trap (DPT)
RAMRandom Access MemoryRandom Access Memory (RAM) RM Relay Module ± ROM Read Only Memory Read Only Memory (ROM) RPM Engine Speed Engine Speed
 SC Supercharger Supercharger
 SCB Supercharger Bypass ±
 SFI Sequential Multiport Fuel Injection Electronic Fuel Injection (EFI), Sequential Injec-
tion
 SPL Smoke Puff Limiter ± SRI Service Reminder Indicator ± SRT System Readiness Test ±
 ST Scan Tool ±
 TB Throttle Body Throttle Body
 TBI Throttle Body Fuel Injection Single Point Injection
Central Fuel Injection (Ci)
 TC Turbocharger Turbocharger TCC Torque Converter Clutch Torque Converter TCM Transmission Control Module Transmission ECU (Electronic Control Unit)
 TP Throttle Position Throttle Position
 TR Transmission Range ±
IN±40± INTRODUCTIONGLOSSARY OF SAE AND TOYOTA TERMS

 
 
TVV 
 
Thermal Vacuum Valve 
 
Bimetallic Vacuum Switching Valve (BVSV)
Thermostatic Vacuum Switching Valve (TVSV)
 TWC Three±Way Catalytic Converter Three±Way Catalytic (TWC)
CC
RO 
TWC+OC
 
Three±Way + Oxidation Catalytic Converter
 
CCR + CCo 
VA F
 
Volume Air Flow
 
Air Flow Meter 
VR
 
Voltage Regulator
 
Voltage Regulator 
VSS
 
Vehicle Speed Sensor
 
Vehicle Speed Sensor (Read Switch Type) 
WOT
 
Wide Open Throttle
 
Full Throttle 
WU±OC
 
Warm Up Oxidation Catalytic Converter
 
± 
WU±TWC
 
Warm Up Three±Way Catalytic Converter
 
Manifold Converter 
3GR
 
Third Gear
 
± 
4GR
 
Fourth Gear
 
±
± INTRODUCTIONGLOSSARY OF SAE AND TOYOTA TERMSIN±41

CIRCUIT DESCRIPTION
To obtain a high purification rate for the Co, Hc and NOx components of the exhaust gas, a three±way catalytic
converter is used, but for most efficient use of the three±way catalytic converter, the air±fuel ratio must be pre-
cisely controlled so that it is always close to the stoichiometric air±fuel ratio.
The oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoi-
chiometric air±fuel ratio. This characteristic is used to detect the oxygen concentration in the exhaust gas and
provide feedback to the computer for control of the air fuel ratio.
When the air±fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen sen-
sor informs the ECM of the LEAN condition (small electromotive force: 0 V).
When the air±fuel ratio is RICHER than the stoichiometric air±fuel ratio the oxygen concentration in the exhaust
gas is reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive force: V).
The ECM judges by the electromotive force from the oxygen sensor whether the air±fuel ratio is RICH or LEAn
and controls the injection duration accordingly. However, if malfunction of the oxygen sensor causes an output
of abnormal electromotive force, the ECM is unable to perform accurate air±fuel ratio control.
The main 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 t(the temperature of the exhaust has is low) current flows to
the heater to heat the sensor for accurate oxygen concentration detection.)
Flange
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater*
1
Coating (Ceramic)
Ideal Air±Fuel Mixture
Richer Ð Air Fuel ratio Ð Leaner
Trouble AreaDTC No.Diagnostic Trouble Code Detecting Condition
Exhaust Gas
Output Voltage
(1)*1Open or snort in heater circuit of main heated
oxygen sensor for 0.5 sec. or more.
(2) (Main heated*1) oxygen sensor signal voltage is
reduced to between 0.35 V and 0.70 V for 60
sec. under conditions (a) ~ (d):
(2) trip detection logic)*
2
(a) Engine coolant temp.: Between 80°C
(176°F and 95°C (203°F)
(b) Engine speed: 1,500 rpm or more
(c) Load driving (Example A/T in Overdrive
(5th for M/T), A/C ON, Flat road, 80 km/h (50
mph))
(d) (Main heated*
1) oxygen sensor signal
voltage: Alternating above and below 0.45 V
Atmosphere

Open or short in heater circuit of main heated
oxygen sensor

Main heated oxygen sensor heater

ECM

(Main heated*
1) oxygen sensor circuit

(Main heated*1) oxygen sensor
HINT: Diagnostic trouble code ª21º is for the (main heated*1) oxygen sensor (Fr) circuit.
Diagnostic trouble code ª28º is for the (main heated*
1) oxygen sensor (Rr) circuit.
*1: Main heated oxygen sensor ONLY for California specification vehicles.
*2: See page EG±397.
DTC 21 28 (Main Heated*1) Oxygen Sensor Circuit
± ENGINE2JZ±GE ENGINE TROUBLESHOOTINGEG±419

See page EG±503.
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three±way
catalytic converter is used, but for 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 oxygen sensor has the characteristic whereby 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
exhaust gas and provide feedback to the computer for control of the air±fuel ratio.
When the air±fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the
oxygen sensor informs the ECM of the LEAN condition (small electromotive force: 0 V).
When the air±fuel ratio is RICHER than the stoichiometric air±fuel ratio the oxygen concentration in the
exhaust gas is reduced and the oxygen sensor informs the ECM of the RICH condition (large electro-
motive force: 1 V).
The ECm judges by the electromotive force from the oxygen sensor whether the air±fuel ratio if RICH
or LEAN and controls the injection duration accordingly. However, if malfunction of the oxygen sensor
causes an output of abnormal electromotive force, the ECM is unable to perform accurate air±fuel ratio
control.
The main heated oxygen sensor include a heater which heats the Zirconia element. The heater is con-
trolled by the ECM. When the intake air volume is low (the temperature of the exhaust has is low) current
flows to the heater to heat the sensor for accurate oxygen concentration detection.)
Diagnostic Trouble Code Detecting ConditionDTC No.Trouble Area
(1) Open or short in heater circuit of main heated
oxygen sensor for 0.5 sec. or more.
(2) Main heated oxygen sensor signal voltage is
reduced to be 0.35 V and 0.70V for 60 sec.
under condition (a) ~ (d):
(2 trip detection logic)*1
(a) Engine coolant temp.: Between 80°C
(176°F) and 95°C (203°F)
(b) Engine speed: 1,500 rpm or more
(c) Load driving (Example A/T in
overdrive (5th for M/T), A/C ON, Flat
road, 80 km/h (50 mph))
(d) Main heated oxygen sensor signal
voltage: Alternating above and below
0.45V

Open or short in heater circuit of main heated
oxygen sensor

Main heated oxygen sensor heater

ECM

Main heated oxygen sensor circuit

Main heated oxygen sensor
DTC 21 Main Heated Oxygen Sensor Circuit
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±525