1986 TOYOTA SUPRA heater

DTC
No.Number of
MIL BlinksCircuitDiagnostic Trouble Code Detecting Condition
Air±Fuel Ratio
Rich Malfunction
(1) Difference 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)*
4
(a) Engine speed: 2,000 rpm or more
(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 o 20 sec. or more under
conditions (a) and (b):
(2 trip detection logic)*
4
(a) Engine speed: 2,000 rpm or more
(b) Engine coolant temp.: Between 60°C (140°F) and
95°C (203°F)
(1) Open or short in heater circuit of sub heated oxygen
sensor for 0.5 sec. or more
(2) Main heated oxygen sensor signal is 0.45 V or more and sub
oxygen sensor signal is 0.45 V or less under conditions (a) ~ (c):
(2 trip detection logic)*
4
(a) Engine coolant temp.: 80°C (176°F) or more
(b) Engine speed: 1,500 rpm or more
(c) Accel. pedal: Fully depressed for 2 sec. or more
(1)*3Open or short in heater circuit of main heated oxygen
sensor (Rr) for 0.5 sec. or more|
(2) (Main heated*3) oxygen sensor (Rr) signal voltage is
reduced to between 0.35 V and 0.70 V for 90 sec.
under conditions (a) ~ (d)
(2 trip detection logic)*
4
(b) 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*3) oxygen sensor (Rr) signal voltage:
Alternating above and below 0.45 V
Sub Heated
Oxygen Sensor
Signal
(Main heated*3)
Oxygen Sensor
Signal (Rr)
*3, 4: See page EG±396, 397 EG±392
± ENGINE2JZ±GE ENGINE TROUBLESHOOTING

 
 
 Trouble Area
 
 
 
Malfunction
Indicator
Lamp*
1
 
 
 Memory*2
 
 
 See page
 
 
Trouble Area
 
 
Normal
Mode 
 
Test
Mode 
 
Memory
 
 
See page
 
 
 
 
 
 
 

Open or 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
 
 
 
 
 
 
 ON
 
 
 
 
 
 
 ON
 
 
 
 
 
 
 
 
 
 
 
 
 
 EG±428
 
 
 
 
 
 

Open or 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
 
 
 
 
 
 
ON
 
 
 
 
 
 
ON
 
 
 
 
 
 

 
 
 
 
 
 
EG 428
 
 
 

Open or short in heater circuit of sub heated oxygen sensor

Sub heated oxygen sensor

ECM
 
 
 
ON
 
 
 
N.A.
 
 
 
 
 
 
 
 
 
 
 
 

Open or short in sub heated oxygen sensor circuit

Sub heated oxygen sensor

ECM
 
 
 
 
 
 
ON
 
 
 
 
 
 
ON
 
 
 
 
 
 

 
 
 
 
 
 
EG±434
 
 
 

Open or short in heater circuit of main heated oxygen sensor (Rr)

Main heated oxygen sensor (Rr) heater

ECM
 
 
 
ON
 
 
 
N.A.
 
 
 
 
 
 
 
 
 
 
 
 
 

(Main heated*3) oxygen sensor (Rr) circuit

(Main heated*3) oxygen sensor (Rr)
 
 
 
 
 
 
 
ON
 
 
 
 
 
 
 
ON
 
 
 
 
 
 
 

 
 
 
 
 
 
 
EG±419
*1, 2, 3: See page EG±396.
± ENGINE2JZ±GE ENGINE TROUBLESHOOTINGEG±393

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

INSPECTION PROCEDURE (Only for California specification vehicles)
HINT: If diagnostic trouble code º21º is output, check the main heated oxygen sensor (Fr) circuit.
If diagnostic trouble code º28º is output, check the main heated oxygen sensor (Rr) circuit.
Check voltage between terminals HT1, HT2 of engine control module
connector and body ground.
Connect SST (check harness ªAº).
See page EG±404)
SST 09990±01000
Measure voltage between terminals HT1, HT2 of engine
control module connector and body ground.
Voltage: 9 Ð 14 V
Go to step
Check main heated oxygen sensor heater.
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)
Replace main heated oxygen sensor.
Check and repair harness or connector between main
relay and main heated oxygen sensor, main heated oxy-
gen sensor and engine control module.
EG±422± ENGINE2JZ±GE ENGINE TROUBLESHOOTING

DTC 27 Sub Heated Oxygen Sensor Circuit (Only for California spec.)
CIRCUIT DESCRIPTION
The sub heated oxygen sensor is installed on the exhaust pipe. Its construction and operation is the same as
the main heated oxygen sensor on page EG±419.
 DTC No. Diagnostic Trouble Code Detecting Condition Trouble Area
 
 
 
 
 
 
 
 
(1) Open or short in heater circuit of sub
heated oxygen sensor for 0.5 sec. or more
 
 
 
 

Open or short in heater circuit of sub heated
oxygen sensor

Sub heated oxygen sensor heater

ECM
 
 
 
 
 
 
 
 
 
27
 
 
 
 
 
 
 
 
 
(2) Main heated oxygen sensor signal is 0.45 V
or more and sub heated oxygen sensor
signal is 0.45 V or less under conditions (a)
~ (c):
(2 trip detection logic)*
(a) Engine coolant temp.: 805C (1765F)
or more
(b) Engine speed: 1,500 rpm or more
(c) Accel. pedal: Fully depressed for 2
sec. or more 
 
 
 
 
 
 
 
 

Open or short in sub heated oxygen sensor
circuit

Sub heated oxygen sensor

ECM
*: See page EG±397. EG±434
± ENGINE2JZ±GE ENGINE TROUBLESHOOTING

Check sub heated oxygen sensor heater.
Disconnect sub heated oxygen sensor connector.
(See page EG±250)
Measure resistance between terminals 1 and 2 of
sub heated oxygen sensor connector.
Resistance: 11 Ð 16
at 20°C (68°F)
Check for open and short in harness and connector between EFI main relay and
engine control module (See page
IN±30).
Replace sub heated oxygen sensor.
Repair or replace harness or connector.
Check and replace engine control module.
Check voltage between terminal HT3 of engine control module connector and
body ground.
Warm up engine to normal operating temperature.
Measure voltage between terminal HT3 of engine
control module connector and body ground, when
engine is idling and racing at 3,500 rpm.
Replace sub heated oxygen sensor.
Check and replace engine control module.
*: It is probable the oxygen sensor has
deteriorated.
Usually, this cannot be confirmed by visual
inspection.
± ENGINE2JZ±GE ENGINE TROUBLESHOOTINGEG±437

Check IGN fuse.
Remove IGN fuse from J/B No.1.
Check continuity of IGN fuse.
Continuity
Check for short in the harness and all the com-
ponents connected to IGN fuse (See Electrical
Wiring Diagram).
Check ignition switch.
(1) Remove finish lower panel and finish lower
panel LH.
(2) Remove heater to register duct No.2.
Check continuity between terminals.
Replace ignition switch.
Check and repair harness and connector between
battery and ignition switch, ignition switch and en-
gine control module.
± ENGINE2JZ±GE ENGINE TROUBLESHOOTINGEG±467

09990±01000Engine Control Computer Check
Harness ªAº
RECOMMENDED TOOLS
09082±00050 TOYOTA Electrical Tester Set
09200±00010Engine Adjust Kit
09258±00030 Hose Plug SetPlug for vacuum hose, fuel
hose etc.
EQUIPMENT
 
 Carburetor cleaner
 
 
 
 Graduated cylinder 
 Injector
 
 
Soft brush 
 
 
 
Sound scope 
 
Injector
 Tachometer 
 
 Torque wrench
 
 
 
 Vacuum gauge 
 
COOLANT
 Item Capacity Classification 
 Engine coolant (w/ Heater) M/T
A/T 
 9.5 liters (10.0 US qts, 8.4 lmp. qts)
9.4 liters (9.9 US qts, 8.3 lmp. qts) 
 Ethylene±glycol base
± ENGINESFI SYSTEM (2JZ±GTE)EG±259