1995 TOYOTA SUPRA coolant

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

CIRCUIT DESCRIPTION
The engine coolant temperature sensor senses the
coolant temperature. A thermistor built in the sensor
changes its resistance value according to the coolant
temperature. The lower the coolant temperature, the
greater the thermistor resistance value, and the high-
er the coolant temperature, the lower the thermistor
resistance value (See Fig. 1).
The engine coolant temperature sensor is connected
to the ECM (See wiring diagram). The 5 V power
source voltage in the ECM is applied to the engine
coolant temperature sensor from the terminal THW
via a resistor R. That is, the resistor R and the engine
coolant temperature sensor are connected in series.
When the resistance value of th engine coolant tem-
perature sensor changes in accordance with changes
in the coolant temperature, the potential at the termi-
nal THW also changes. Based on this signal, the ECM
increases the fuel injection volume to improve drive-
ability during cold engine operation. If the ECM re-
cords the diagnostic trouble code 22, it operates the
fail safe function in which the engine coolant tempera-
ture is assumed to be 80°C (176°F).
Diagnostic Trouble Code Detecting ConditionDTC No.Trouble Area
Open or short in engine coolant temp. sensor
circuit for 0.5 sec. or more
Open or short in engine coolant temp.
sensor circuit

Engine coolant temp. sensor

ECM
DTC 22 Engine Coolant Temp. Sensor Circuit
EG±530± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

(See page EG±510)
(1) Connect SST (check harness ªAº).
(See page EG±510)
(2) Turn ignition switch ON
Measure voltage between terminals THW and
E2 of engine control module connector.
Check voltage between terminals THW and E2 of engine control module
connector.
Check for intermittent problems.
(See page EG±505)
Disconnect the engine coolant temp. sensor con-
nector.
Measure resistance between terminals.
Resistance is within Acceptale Zone on chart.
Check engine coolant temp. sensor.
Replace engine coolant temp. sensor.
Repair or replace harness or connector.
Check and replace engine control module.
Check for open and short in harness and connector between engine control
module and engine coolant temp. sensor (See page IN±30).
INSPECTION PROCEDURE
HINT: If diagnostic trouble codes º22º (engine coolant temperature sensor circuit), º24º (intake air temperature
sensor circuit) and º41º (throttle position sensor circuit) are output simultaneously, E2 (sensor ground)
may be open.
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±531

DTC 24 Intake Air Temp. Sensor Circuit
CIRCUIT DESCRIPTION
The intake air temp. sensor is built into the mass air flow meter and senses the intake air temperature. The struc-
ture of the sensor and connection to the ECM is the same as in the engine coolant temp. sensor shown on page
EG±530.
If the ECM detects the diagnostic trouble code º24º, it operates the fail safe function in which the intake air tem-
perature is assumed to be 20°C (68°F).
 
 DTC No.
 
 Diagnostic Trouble Code Detecting Condition
 


Trouble Area
 
 
 
 
24
 
 
 
 
Open or short in intake air temp. sensor circuit
for 0.5 sec. or more
 





Open or short in intake air temp. sensor

Circuit

Intake air temp. sensor

ECM
EG±532± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

(See page EG±510)
(1) Connect SST (check harness ªAº).
(See page EG±510)
SST 09990±01000
(2) Turn ignition switch ON
Measure voltage between terminals THW and E2
of engine control module connector.
Check voltage between terminals THA and E2 of engine control module
connector.
Check for intermittent problems.
(See page EG±505)
Disconnect the mass air flow meter connector.
Measure resistance between terminals 3 and 4
of mass air flow meter connector.
Resistance is within Acceptable Zone on chart.
Check intake air temp. sensor.
Check for open and short in harness and connector between engine
control module and intake air temp. sensor (See page IN±30)
Replace intake air temp. sensor (Replace
mass air flow meter).
Repair or replace harness or connector.
Check and replace engine control module.
INSPECTION PROCEDURE
HINT: If diagnostic trouble codes º22º (engine coolant temperature sensor circuit), º24º (intake air temperature
sensor circuit) and º41º (throttle position sensor circuit) are output simultaneously, E2 (sensor ground)
may be open.
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±533

DTC 25 26 Air±Fuel Ratio Lean Rich Malfunction
CIRCUIT DESCRIPTION
See EG±525 for the circuit description.
 DTC No. Diagnostic Trouble Code Detecting Condition Trouble Area
 
 
 
 
 
 
 
 
 
 
 
 
 
 
(1) Main heated oxygen sensor voltage is
0.45 V or less (lean) for 90 sec. under
conditions (a) and (b):
(2 trip detection logic)*
2
(a) Engine coolant temp.: 70°C (158°F)
or more
(b) Engine speed: 1,500 rpm or more
 
 
 
 
 
 
 

Open or short in main heated oxygen
sensor circuit

Main heated oxygen sensor

Ignition system

ECM
 
 
 
 
 
 
 
 
25 
 
 
 
 
 
 
 
(2) Engine speed varies by more than 20 rpm
over the preceding crank angle period
during a period of 25 sec. or more under
conditions (a) and (b):
(2 trip detection logic).*
(a) Engine speed: Below 950 rpm
(b) Engine coolant temp.: 80°C
(176°F) or
more 
 
 
 
 
 
 
 

Open and short in injector circuit

Fuel line pressure (injector leak, blockage)

Mechanical system malfunction
(skipping teeth of timing belt)

Ignition system

Compression pressure (foreign object
caught in valve)

Mass air flow meter (air intake)

ECM
 
 
 
 
 
 
 
 
26
 
 
 
 
 
 
 
 
Engine speed varies by more than 20 rpm over
The preceding crank angle period during a
Period of 25 sec. or more under conditions (a)
And (b):
(2 trip detection logic).*
(a) Engine speed: Below 950 rpm
(b) Engine coolant temp.: 80°C
(176°F) or
more 
 
 
 
 
 
 
 

Open and short in injector circuit

Fuel line pressure (injector leak, blockage)

Mechanical system malfunction
(skipping teeth of timing belt)

Ignition system

Compression pressure (foreign object
caught in valve)

Mass air flow meter (air intake)

ECM
*: See page EG±503. EG±534
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

(See page EG±9).
EG±261
IG±21
EG±568
EG±583
EG±530
EG±532
EG±544
EG±33
Check each circuit found to be a possible cause of trouble according to the results of the check in
Check each item found to be a possible cause of problem.
Check for open and short in harness and connector between engine
control module and main heated oxygen sensor, engine control module
and data link connector 1 (See page IN±30).
The numbers int he table below show the order in which the checks should be done.
Repair or replace harness or connector.
Repair or replace.
Replace main heated oxygen sensor.
Repair or replace.
Check and replace engine control module.
Check compression (See page EG±9).
Does malfunction disappear when a good main heated oxygen sensor is
installed?
Faulty sensor installation
Air leakage
Misfire
Fuel system
Injector circuit
Characteristics deviation
in engine coolant temp. sensor
Characteristics deviation
in intake air temp. sensor
Characteristics deviation in mass
air flow meter
Va l v e t i m i n g
Main heater oxygen sensor signal
continues at 0 V
EG±538± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

EG±583
IG±21
EG±33
EG±261
EG±568
EG±544
EG±530
EG±532
EG±9).
Check each circuit found to be a possible cause of trouble according to the results of the check in
Check each item found to be a possible cause of problem.
The numbers int he table below show the order in which the checks should be done.
Air leakage
Misfire
Fuel system
Injector circuit
Characteristics deviation
in engine coolant temp. sensor
Characteristics deviation
in intake air temp. sensor
Characteristics deviation in mass
air flow meter
Va l v e t i m i n g
Main heater oxygen sensor signal
continues at 5.0 VMain heater oxygen sensor
signal is normal
Check compression (See page EG±9).
Repair or replace.
Repair or replace.
Repair main heated oxygen sensor.
Check and replace engine control module.
Does malfunction disappear when a good main heated oxygen sensor is
installed?
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±539