TOYOTA SUPRA 1995 Service Repair Manual

DTC 16 A T Control Signal Malfunction
CIRCUIT DESCRIPTION
The signal from the A/T CPU retards the ignition timing of the engine during A/T gear shifting, thus momentarily
reducing torque output of the engine for smooth clutch operation inside the transmission and reduced shift
shock.
 
 DTC No.
 
 Diagnostic Trouble Code Detecting Condition
 
 Trouble Area
 
 16
 
 
Fault in communications between the engine
CPU and A/T CPU in the ECM 
 
ECM
If the ECM detects the diagnostic trouble code º16º in memory, it prohibits the torque control of the A/T which
performs smooth gear shifting.
INSPECTION PROCEDURE
Are there any other codes (besides Code 16) being output?
Go to relevant diagnostic trouble code chart.
Replace engine control module.
EG±524± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

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 (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: Main Heated Oxygen Sensor Deterioration
It is vital that this test routine is adhered to detect the malfunction:
(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 with all ACC switch OFF.
(3) Idle the engine for 3 min.
(4) Accelerate gradually within the range 1,300 ~ 1,7700 rpm (centered around 1,500 rpm) with
the A/C switch ON and D position for A/T (5th for M/T).
HINT:
Ensure engine rpm does NOT fall below 1200 rpm.

Gradually depress the accelerator pedal at a suitable rate to comply with the test re±
quirements on the above graph.

Never allow engine rpm to drop at any time during the test.
(5) Maintain the vehicle speed at 64 Ð 80 km/h (40 Ð 50 mph).
(6) Keep the vehicle running for Ð 2 min. after starting acceleration.
HINT: If a malfunction exists, the Malfunction Indicator Lamp will light up after approx. 60 sec.
from the start of acceleration.
NOTICE: If the conditions in this test are not strictly followed, detection of the malfunc±
tion will not be possible. EG±526
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

Connect SST (check harness ªAº).
(See page EG±510)
SST 09990±01000
Measure voltage between terminals HT1 of engine
control module connector and body ground.
Voltage: 9 Ð 14 V
Check voltage between terminals HT1 of engine control module
connector and body ground.
INSPECTION PROCEDURE
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±527

Disconnect main heated oxygen sensor connector.
Measure resistance between terminals 1 and 2 of
main heated oxygen sensor connector.
Resistance: 11 Ð 16
at 20°C (68°F)
Check main heated oxygen sensor heater.
Replace main heated oxygen sensor.
Check and repair harness or connector between
main relay and main heated oxygen sensor, main
heated oxygen sensor and engine control module.
Warm up engine to normal operating temperature.
Measure voltage between terminals HT1 of engine
control module connector and body ground, when
engine is idling and racing at 4,000 rpm.
Check voltage between terminals HT1 of engine control module connector
and body ground.
Replace main heated oxygen sensor.*
Check and replace engine control module.
In the 4,000 rpm racing check, continue engine
racing at 4,000 rpm for approx. 20 seconds or
more.
*: It is probable the oxygen sensor has deteri±
orated. Usually, this cannot be confirmed by
visual inspection. EG±528
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

With the engine racing (4,000 rpm) measure
waveform between terminals OX1 and E1 of
engine control module.
HINT: The correct waveform is as shown oscillating
between approx. 0.1 V and 0.9 V
If the oxygen sensor has deteriorated, the amplitude of the
voltage will be reduced as shown on the left.
ReferenceINSPECTION USING OSCILLOSCOPE
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±529

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