1995 TOYOTA SUPRA traction control

[2] SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK
The diagnostic system in the TOYOTA SUPRA fulfills various functions. The first function is the Diagnostic
Trouble Code Check in which a malfunction in the signal circuits to the ECU is stored in code in the ECU memory
at the time of occurrence, to be output by the technician during troubleshooting. Another function is the Input
Signal Check which checks if the signals from various switches are sent to the ECU correctly. The air condition-
ing system has an Actuator Check function whereby the ECU automatically operates the actuators of the damp-
er and blowermotor, etc. to check the operation. By using these check functions, the problem areas can be nar-
rowed down quickly and troubleshooting can be performed effectively. Diagnostic functions are incorporated
in the following systems in the TOYOTA SUPRA.
 
 System
 
 
Diagnostic Trouble
Code Check 
 
Input Signal Check
(Sensor Check) 
 
Other Diagnosis
Function
 
 
 
 
 
 
Engine
Automatic Transmission
Anti±Lock Brake
Traction Control (Option)
Supplemental Restraint System
Cruise Control
Air Conditioning 
 
 
 
 
 
O (with Test Mode)
O (with Test Mode)
O
O
O
O
O 
 
 
 
 
 
O
O
O
O
O
O 
 
 
 
 
 Actuator Check
In diagnostic trouble code check, it is very important to determine whether the problem indicated by the diagnos-
tic trouble code is still occurring or occurred in the past but returned to normal at present. In addition, it must
be checked in the problem symptom check whether the malfunction indicated by the diagnostic trouble code
is directly related to the problem symptom or not. For this reason, the diagnostic trouble codes should be
checked before and after the symptom confirmation to determine the current conditions, as shown in the table
below. If this is not done, it may, depending on the case, result in unnecessary troubleshooting for normally oper-
ating systems, thus making it more difficult to locate the problem, or in repairs not pertinent to the problem.
Therefore, always follow the procedure in correct order and perform the diagnostic trouble code check.
DIAGNOSTIC TROUBLE CODE CHECK PROCEDURE
 
 
 
Diagnostic Trouble
Code Check (Make a
note of and then clear) 
 
 
Confirmation of
symptoms 
 
 
Diagnostic Trouble
Code Check 
 
 
Problem Condition
 
 
Diagnostic
Trouble Code
Display 
 
Problem symptoms
exist 
 
Same Diagnostic
trouble code is dis-
played 
 
Problem is still occurring in the diagnos-
tic circuit
 
 
 
 
 
%
 
 
 
 
 
 
 
 
 
 
Normal code is dis-
played 
 
 
 
 
The problem is still occurring in a place
other than in the diagnostic circuit. (The
diagnostic trouble code displayed first is
either for a past problem or it is a sec-
ondary problem.)
 
 %
 
 
No problem
symptoms exist 
 
 
 
The problem occurred in the diagnostic
circuit in the past.
 
 
Normal Code Display
%
 
 
Problem symptoms
exist 
 
Normal code is dis-
played 
 
The problem is still occurring in a place
other than in the diagnostic circuit.
 
 %
 
 
No problem
symptoms exist 
 
Normal code is dis-
played 
 
The problem occurred in a place other
than in the diagnostic circuit in the past.
IN±22± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

 RH Right±Hand
 SRS Supplemental Restraint System
 SSM Special Service Materials
 SST Special Service Tools
 STD Standard
 SW Switch TEMP. Temperature TRAC Traction Control System 
 U/S 
 Undersize
 VSV Vacuum Switching Valve
 w/ With
 w/o Without
IN±38± INTRODUCTIONABBREVIATIONS USED IN THIS MANUAL

(See page EG±397).
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 NOx emission. The amount
of EGR is regulated by the EGR vacuum modulator according to the load.
If even one of the following conditions is fulfilled,
the VSV is turned ON by a signal from the ECM.
This results 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 5,200 rpm

Traction control is operating
DTC No.Diagnostic Trouble Code Detecting ConditionTrouble Area
EGR gas temp. is 70°C (158°F) or less for 1 ~
4 min. under conditions (a) and (b):
(2) trip detection logic)*
(a) Engine coolant temp.: 63°C (145°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)

Open in EGR gas temp. sensor circuit

Short in VSV circuit for EGR

EGR hose disconnected, valve stuck

Clogged EGR gas passage

ECM
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 by confirming that diag±
nostic trouble code is no longer detected.
DTC 71 EGR System Malfunction
± ENGINE2JZ±GE ENGINE TROUBLESHOOTINGEG±453

CIRCUIT DESCRIPTION
The throttle position sensor is mounted in the throttle
body and detects the the throttle valve opening angle.
When the throttle valve is fully closed, the IDL contacts
in the throttle position sensor are on, so the voltage at
the terminal IDL of the ECM becomes 0 V. At this time,
a voltage of approximately 0.7 V is applied to the termi-
nal VTA of the ECM. When the throttle valve is opened,
the IDL contacts go off and thus the power source volt-
age of approximately 12 V in the ECM is applied to the
terminal IDL of the ECM. The voltage applied to the ter-
minal VTA of the ECM increases in the proportion to
the opening angle of the throttle valve and becomes
approximately 3.2 ± 4.9 V when the throttle valve is ful-
ly opened. The ECM judges the vehicle driving condi-
tions from these signals input from the terminals VTA
and IDL, and uses them as one of the conditions for de-
ciding the air±fuel ratio correction, power increase
corrections and fuel±cut control etc. The sub±throttle
position sensor is built and operates in the same way
as the main throttle position sensor. This sensor is
used for traction control. The sub±throttle valve is
opened and closed by the sub±throttle actuator ac-
cording to signals from the TRAC ECU to control the
engine output.
Open or short in throttle position sensor circuit
for 0.5 sec. or more
Open or short in sub±throttle position sensor
circuit for 0.5 sec. or more

Open or short in throttle position sensor
circuit

Throttle position sensor

ECM

Open or short in sub±throttle position
sensor circuit

Sub±throttle position sensor

ECM
HINT:
Diagnostic trouble code 41 is for the throttle position sensor circuit.
Diagnostic trouble code 47 is for the sub±throttle position sensor circuit.

When the connector for the throttle position sensor(s) is disconnected, diagnostic trouble code 41
or 47 is not displayed. Diagnostic trouble code 41 or 47 is displayed only when there is an open
or short in the VTA signal circuit of the throttle position sensor(s).

Signals from the throttle position sensor(s) are also input to the TRAC ECU, so when a malfunc±
tion occurs on the TRAC side, code 41 or 47 may be displayed.
DTC 41 47 Throttle Position Sensor(s) Circuit
EG±552± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING