1986 TOYOTA SUPRA Service Repair Manual

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

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

HINT: Before this test, check the feedback voltage for oxygen sensor.
(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.
(3) Idle the engine for 3 min.
(4) Race the engine quickly to 4,000 rpm 3 times using the accelerator pedal.
(5) 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.
Malfunction: Open or Short in Main Heated Oxygen Sensor
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.
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±535