TOYOTA SUPRA 1995 Service Repair Manual

Check voltage between terminals HT1, HT2 of engine control module
connector and body ground.
INSPECTION USING OSCILLOSCOPE
Replace main heated oxygen sensor.*
Check and replace engine control module.
*: It is probable the oxygen sensor has deteriorated.
Usually, this cannot be confirmed by visual inspec±
tion.
Warm up engine to normal operating temperature.
Measure voltage between terminals HT1, HT2 of
engine control module connector and body ground.
when engine is idling and racing at 4,000 rpm.
In the 4,000 rpm racing check, continue engine rac-
ing at 4,000 rpm for approx. 20 seconds or more.

With the engine racing (4,000 rpm) measure wave±
form between terminals OX1, OX2 and E1 of engine
control module.
HINT: The correct waveform is as shown, oscillating be
tween approx. 0.1 V nd 0.9 V
If the oxygen sensor has deteriorated, the ampli±
tude of the voltage will be reduced as shown on the
left.
± ENGINE2JZ±GE ENGINE TROUBLESHOOTINGEG±423

DTC 22 Engine Coolant Temp. Sensor Circuit
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 higher
the coolant temperature, the lower thermistor resist-
ance 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 tem-
perature sensor from the terminal THW via a resistor R.
That is, the resistor R an the engine coolant temperature
sensor are connected in series. When the resistance
value of the engine coolant temperature sensor
changes in accordance with the changes in the coolant
temperature the potential at the terminal THW also
changes. Based on this signal, the ECM increases the
fuel injection volume to improve driveability during cold
engine operation. If the ECM detects the diagnostic
trouble code 22, it operates the fail safe function in
which the engine coolant temperature is assumed to be
80°C (176°F).
DTC No.Diagnostic Trouble Code Detecting ConditionTrouble Area
Open or short in engine coolant temp. sen-
sor circuit for 0.5 sec. or more

Open or short in engine coolant temp.
sensor circuit

Engine coolant temp. sensor

ECM
Reference
VoltageEngine Coolant
Temp.
Resis±
tance
EG±424± ENGINE2JZ±GE ENGINE TROUBLESHOOTING

(See page EG±404)
(1) Connect SST (check harness ªAº).
(See page EG±404)
(2) Turn ignition switch ON.
Measure voltage between terminals THW and E2
of engine control module connector.
Check for intermittent problems.
(See page EG±399)
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).
Disconnect the engine coolant temp. sensor connector.
Measure voltage between terminals.
Resistance is within Acceptable Zone on chart.
Check voltage between terminals THW and E2 of engine control module con±
nector.
VoltageEngine Coolant Temp.
(Engine is cool)
(Engine is hot)
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±GE ENGINE TROUBLESHOOTINGEG±425

DTC 24 Intake Air Temp. Sensor Circuit
CIRCUIT DESCRIPTION
The intake air temp. sensor is built into the volume air flow meter and senses the intake air temperature.
The structure of the sensor and connection to the ECM is the same as in the engine coolant temp. sensor shown
on page EG±424.
If the ECM detects the diagnostic trouble code º24º, it operates the fail safe function in which the
intake air temper-
ature
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 
Open or short in intake air temp. sensor circuit

Intake air tempsensor 
 
24 
 
Oen or short in intake air tem . sensor circuit for
0.5 sec. or more 
 

Intake air temp. sensor

ECM
EG±426± ENGINE2JZ±GE ENGINE TROUBLESHOOTING

(See page EG±404)
(1) Connect SST (check harness ªAº).
(See page
EG±404)
SST 09990±01000
(2) Turn ignition switch ON.
Measure voltage between terminals THW and E2 of en-
gine control module connector.
Check for intermittent problems.
(See page EG±399)
Check intake air temp. sensor.
Disconnect the volume air flow meter connector.
Measure voltage between terminals 1 and 2 of volume
air flow meter connector.
Resistance is within Acceptable Zone on chart.
Check voltage between terminals THA and E2 of engine control module con±
nector.
Replace intake air temp. sensor (Replace vol-
ume air flow meter).
Check for open and short in harness and connector between engine control
module and intake air temp. sensor (See page IN±30).
Repair or replace harness or connector.
Check and replace engine control module.
VoltageIntake air temp.
ResistanceIntake air temp.
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±GE ENGINE TROUBLESHOOTINGEG±427

CIRCUIT DESCRIPTION
See page EG±419 for the circuit description
DTC No.Diagnostic Trouble Code Detecting ConditionTrouble Area
(1) (Main heated*1) oxygen sensor voltage is
0.45 V or less (lean) for 90 sec. under codi±
tions (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
(2)*1Difference of air±fuel ratio feedback
compensation value between front (No.
1 ~ 3 cylinders) and rear (No. 4 ~ 6
cylinders) is more than 15 percentage for
20 sec. or more under conditions (a)
and (b):
(2 trip detection logic)*
2
(a) Engine speed: 2,000 rpm or more
(b) Engine coolant temp.: Between 60°C
(140°F) and 95°C (203°F)
(1)*1Difference of air±fuel ratio feedback
compensation value between front (No.
1 ~ 3 cylinders) and rear (No. 4 ~ 6
cylinders) is more than 15 percentage for
20 sec. or more under conditions (a)
and (b):
(2 trip detection logic)*
2
(a) Engine speed: 2,000 rpm or more
(b) Engine coolant temp.: Between 60°C
(140°F) and 95°C (203°F)
(3)*1Engine speed varies by more than 15 rpm
over the preceding crank angle period
during a period of 20 sec. or more under
conditions (a) and (b):
(2 trip detection logic)*
2
(a) Engine speed: Idling
(b) Engine coolant temp.: Between 60°C
(140°F) and 95°C (203°F)
(2) Engine speed varies by more than 15 rpm
over the preceding crank angle period
during a period of 20 sec. or more under
conditions (a) and (b):
(2 trip detection logic)*
2
(a) Engine speed: Idling
(b) Engine coolant temp.: Between 60°C
(140°F) and 95°C (203°F)
*1: Only for California specification vehicles
*
2: See page EG±397.

Open or short in (main heated*1) oxygen
sensor circuit

(Main heated*
1) oxygen sensor

Ignition system

ECM

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)

Volume air flow meter (air intake)

ECM

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)

Volume air flow meter (air intake)

ECM

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)

Volume air flow meter (air intake)

ECM

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)

Volume air flow meter (air intake)

ECM
DTC 25 26 Air±Fuel Ratio Lean Rich Malfunction
EG±428± ENGINE2JZ±GE ENGINE TROUBLESHOOTING

CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diagnostic trouble code detecting condition after diagnostic trouble code is recorded.
(b) To check that the malfunction is corrected when the repair is completed confirming that diagnostic
trouble code is no longer detected.
Malfunction: Open or Short in (Main Heated*) Oxygen Sensor
HINT: Before this test, check the feedback voltage for oxygen sensor.
(1) Disconnect the EFI No.1 fuse (30 A) for 10 sec. or more, with IG switch OFF. Initiate test
mode (Connect terminal TE2 and E1 of data link connector 2 with IG switch OFF).
(2) Start the engine and warm up.
(3) Idle the engine for 3 min.
(4) Race the engine at 2,000 rpm for 90 sec.
HINT: If a malfunction exists, the malfunction indicator lamp will light up during step (4).
NOTICE: If the conditions in this test are not strictly followed, detection of the malfunction
will not be possible.
± ENGINE2JZ±GE ENGINE TROUBLESHOOTINGEG±429

See page
EG±421
(1) Disconnect the EFI No.1 fuse (30A) for 10 sec. or more, with IG switch OFF.
Initiate test mode (Connect terminal TE2 and E1 of data link connector 2
with IG switch OFF).
(2) Start the engine and warm up with all ACC switched OFF.
(3) Idle the engine for 5 min.
(After the engine is started, do not depress the accelerator pedal.)
(4) If the malfunction is not detected during idling, racing the engine without any load at
approx. 2,000 rpm for 60 sec.

HINT: If a malfunction exists, the malfunction indicator lamp will light up during the 5 min. idling
period or within 60 sec. of starting racing.
NOTICE: If the conditions in this test are not strictly followed, detection of the malfunction
will not be possible.
CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diagnostic trouble code detecting condition after diagnostic trouble code is recorded.
(b) To check that the malfunction is corrected when the repair is completed confirming that diagnostic
trouble code is no longer detected.
Malfunction: Open or Short in Injector circuit, Injector Leak or Blockage.
WIRING DIAGRAM
See page EG±421 for the WIRING DIAGRAM.
*: Only for California specification vehicles
EG±430± ENGINE2JZ±GE ENGINE TROUBLESHOOTING

(1) Warm up engine to normal operating temperature.
(2) Using SST, connect terminal TE1 and E1 of data link
connector 1.
SST 09843±18020
(3) Connect positive probe to terminal VF1, VF2 and
negative probe to terminal E1 of data link connector
1.
(1) Warm up the oxygen sensor by racing engine at
2,500 rpm for about 2 minutes.
(2) Then, still maintaining engine at 2,500 rpm, count
how many times voltmeter fluctuates needle
between 0 and 5 V.
Warm up engine to normal operating temperature
Measure voltage between terminals OX1, OX2
and E1 of data link connector 1 when engine is
suddenly raced to full throttle.
The voltage should be 0.5 V or higher at least
once.
Inspection should not take longer 1 second.
Check voltage between terminals OX1, OX2 and E1 of data link connector 1.
Check voltage between terminals VF1, VF2 and E1 of data link connector 1.
Needle fluctuates 8 times or more for
Result
every ten seconds
Continue at 0 V
Continue at 5 V
INSPECTION PROCEDURE
± ENGINE2JZ±GE ENGINE TROUBLESHOOTINGEG±431

EG±47
2
IG±4
EG±33
EG±190
EG±457
EG±438
EG±424
EG±426
Check for open and short in harness and connector between engine control mod-
ule and (main heated*) oxygen sensor, engine control module and data link connec-
tor 1 (see page
IN±30).
Check each item found to be a possible cause of problem.
Repair or replace harness or connector.
Repair or replace.
Repair or replace.
Replace (main heated*) oxygen sensor.
Check and replace engine control module.
Does malfunction disappear when a good (main heated*) oxygen sensor is
installed?
Check compression (See page EG±9).
Check each circuit found to be a possible cause of trouble according to the results of the check in
The numbers in the table below show the order in which the checks should be done.
(Main heated*) oxygen sensor
signal from either side
continues at 0 V(Main heated*) oxygen sensor
signal from both sides
continues at 0 V
Possible CauseSee page
Faulty sensor installation
Injector circuit
Misfire
Valve timing
Air leakage
Fuel system
Characteristics deviation
in volume air flow meter
Characteristics deviation
in engine coolant temp. sensor
Characteristics deviation
in intake air temp. sensor
*: Only for California specification vehicles EG±432
± ENGINE2JZ±GE ENGINE TROUBLESHOOTING