1986 TOYOTA SUPRA engine coolant

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

DTC 27 Sub Heated Oxygen Sensor Circuit
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±525.
 
 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±503. EG±540
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

INSPECTION PROCEDURE
HINT:
wIf diagnostic trouble code 41 is displayed, check throttle position sensor circuit. If diagnostic trouble code
47 is displayed, check sub±throttle position sensor circuit.
wIf diagnostic trouble code 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.
(See page EG±505)
(See page EG±510)
(See page EG±292)
Check voltage between terminals VTA1, 2, IDL1, 2 and E2 of engine control
module connector.
The voltage should increase steadily in proportion
to the throttle valve opening angle.
(1) Connect SST (check harness ªAº).
(See page EG±510)
SST 09990±01000
(2) Turn ignition switch ON.
(3) For throttle position sensor, disconnect the vacuum
hose from the throttle body, then apply vacuum to
the throttle opener.
(See page EG±292)
(4) For sub±throttle position sensor, remove intake air
duct and disconnect sub±throttle valve step motor
connector.
Measure voltage between terminals VTA1, 2, IDL1,
2 and E2 of engine control module connector when
the (sub±) throttle valve is opened gradually from
the closed condition.
Check for intermittent problems.
(See page
EG±505)
Throttle Valve
Terminal
Fully Closed
Fully Open
EG±554± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

DTC 42 No. 1 Vehicle Speed Sensor Signal Circuit
CIRCUIT DESCRIPTION
The No.1 vehicle speed sensor outputs a 4±pulse signal for every revolution of the rotor shaft, which
is rotated by the transmission output shaft via the driven gear. After this signal is converted into a more
precise rectangular waveform by the waveform shaping circuit inside the odometer and trip meter, it is
then transmitted to the engine control module. The ECM determines the vehicle speed based on the
frequency of these pulse signals.
DTC No.Diagnostic Trouble Code Detecting ConditionTrouble Area
For A/T
All conditions below are detected
Continuously for 8 sec. or more:
(a) No.1 vehicle speed signal: 0 km/h
(mph)
(b) Engine speed: 3,000 rpm or more
(c) Park/neutral position switch: OFF
(d) Stop light switch: OFF
For A/T
All conditions below are detected
Continuously for 8 sec. or more:
(a) No.1 vehicle speed signal: 0 km/h
(mph)
(b) Engine speed: Between 1,500 rpm
and 4,000 rpm
(c) Engine coolant temp.: 80°C (176°F)
or more
(d) Load driving

No.1 vehicle speed sensor

Telltale light RH (Odometer and trip meter)

Open or short in No.1 vehicle speed sensor
circuit

ECM
HINT: In test mode, diagnostic trouble code 42 is output when vehicle speed is 5 km/h (3 mph) or
below.

Waveform between terminals SP1 and E1 when vehicle
speed is approx. 20 km/h (12mph).
HINT: As the vehicle speed increases, the number of signals
from SP1 increases. EG±556
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

See page EG±503.
CIRCUIT DESCRIPTION
The EGR system is designed to recirculate the exhaust gas, controlled according to the driving condi-
tions back into the intake air±fuel mixture. It helps to slow down combustion in the cylinder and thus
lower the combustion temperature which, in turn, reduces the amount of NO
x emission. The amount
of EGR is regulated by the EGR vacuum modulator according to the engine load.
If even one of the following conditions is fulfilled,
the VSV is turned ON by a signal from the ECM.
This resists in atmospheric air acting on the EGR
valve, closing the EGR valve and shutting off the
exhaust gas (EGR cut±OFF).

Engine coolant temp. below 50°C (122°F)

During deceleration (throttle valve closed)

Light engine load (amount of intake air very
small)

Engine speed over 4,800 rpm

Manifold absolute pressure more than 120 kPa
(1.2 kgf/cm
2, 17.4 psi)
DTC No.Diagnostic Trouble Code Detecting ConditionTrouble Area
No No.1 knock sensor signal to ECM for 4
crank revolutions with engine speed between
2,050 rpm and 5,950 rpm

Open EGR gas temp. sensor circuit

Short in VSV circuit for EGR

EGR hose disconnected, valve stuck

Clogged EGR gas passage

ECM
EGR gas temp. and intake air temp. are
60°C(140°F) or less for A/T, 55°C (131°F) or
less for M/T for 1 ~ 4 min. under conditions (a)
and (b):
(2 trip detection logic)*
(a) Engine coolant temp.: 60°C (140°F) or
more
(b) EGR operation possible (Example A/T in
3rd speed (5th for M/T), A/C ON, 96 km/h
(60 mph), Flat road)
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 by confirming that diagnos±
tic trouble code is no longer detected.
DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN
DTC 71 EGR System Malfunction
EG±564± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

VSV Circuit for Fuel Pressure Control
CIRCUIT DESCRIPTION
The ECM turns on a VSV (Vacuum Switching
Valve) to draw air into the diaphragm chamber
of the pressure regulator if it detects that the
temperature of the engine coolant is too high
during engine starting.
The air drawn into the chamber increases the
fuel pressure to prevent fuel vapor lock at high
engine temperature in order to help the en-
gine start when it is warm.
Fuel pressure control ends approx. 120 sec.
after the engine is started.
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±595