display TOYOTA SUPRA 1995 Service Service Manual

Tc Terminal Circuit
CIRCUIT DESCRIPTION
By connecting terminals Tc and E1 of DLC1 or DLC2, the ECU displays the diagnostic trouble code
by blinking the TRAC indicator light.
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±163

[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

Taking into account the above points, a flow chart showing how to proceed with troubleshooting using the diag-
nostic trouble code check is shown below. This flow chart shows how to utilize the diagnostic trouble code check
effectively, then by carefully checking the results, indicates how to proceed either to diagnostic trouble code
troubleshooting or to troubleshooting of problem symptoms.
Diagnostic trouble code check
Making a note of and clearing of the diagnostic trouble codes displayed
Symptom confirmation
No problem symptoms
existProblem symptoms
exist
Simulation test using the symptom
simulation methods
Diagnostic trouble code check

Diagnostic trouble code
displayed

Problem symptoms exist
Normal code displayed

Problem symptoms exist
Normal code displayed

No Problem symptoms
exist
Troubleshooting of problem
indicated by diagnostic rouble
codeTroubleshooting of each
problem symptom
System Normal
If a diagnostic trouble code was dis-
played in the initial diagnostic trouble
code check, it indicates that the trouble
may have occurred in a wire harness or
connector in that circuit in the past.
Therefore, check the wire harness and
connectors (See page
IN±30).
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSIN±23

[4] DIAGNOSTIC TROUBLE CODE CHART
The inspection procedure is shown in the table below. This table permits efficient and accurate troubleshooting
using the diagnostic trouble codes displayed in the diagnostic trouble code check. Proceed with troubleshooting
in accordance with the inspection procedure given in the diagnostic chart corresponding to the diagnostic
trouble codes displayed. The engine diagnostic trouble code chart is shown below as an example.
IN±26± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

[5] MATRIX CHART OF PROBLEM SYMPTOMS
The suspect circuits or parts for each problem symptom are shown in the table below. Use this table to trouble-
shoot the problem when a ºNormalº code is displayed in the diagnostic trouble code check but the problem is
still occurring. Numbers in the table indicate the inspection order in which the circuits or parts should be checked.
HINT: When the problem is not detected by the diagnostic system even though the problem symptom is present,
it is considered that the problem is occurring outside the detection range of the diagnostic system, or that the
problem is occurring in a system other than the diagnostic system.
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSIN±27

System normal

Source voltage drop

Short in squib circuit or front
airbag sensor circuit (to ground)

Front airbag sensor
center airbag sensor
assembly malfunction

Short in squib circuit (to B+)

Open in front airbag sensor
circuits

Short in driver airbag squib circuit
(between D+ wire harness and D±
wire harness)

Open in driver airbag squib circuit

Open in front airbag sensor circuit

SRS warning light system mal±
function

Center airbag sensor assembly
malfunction

Short in front passenger airbag
squib circuit

Open in front passenger airbag
squib circuit

Battery

Center airbag sensor assembly

Squib (driver airbag and front pas±
senger airbag)

Front airbag sensor

Spiral cable

Center airbag sensor assembly

Wire harness

Squib (driver airbag and front pas±
senger airbag)

Front airbag sensor

Spiral cable

Center airbag sensor assembly

Wire harness

Steering wheel pad (squib)

Spiral cable

Center airbag sensor assembly

Wire harness

Steering wheel pad (squib)

Spiral cable

Center airbag sensor assembly

Wire harness

Front airbag sensor

Center airbag sensor assembly

Wire harness

SRS warning light

Center airbag sensor assembly

Wire harness

Center airbag sensor assembly

Front passenger airbag assembly
(squib)

Center airbag sensor assembly

Wire harness

Front passenger airbag assembly
(squib)

Center airbag sensor assembly

Wire harness
HINT:
*
1
wWhen the SRS warning light remains lit up and the diagnostic trouble code is the normal code, this means
a source voltage drop.
This malfunction is not stored in memory by the center airbag sensor assembly and if the power source
voltage returns to normal, after approx. 10 seconds the SRS warning light will automatically go out.
*
2
wCode 22 is recorded when a malfunction occurs in the SRS warning light system.
If an open malfunction occurs in the SRS warning light system, the SRS warning light does not light up,
so that until the malfunction is repaired, the diagnostic trouble codes (including code 22) cannot be con-
firmed.
wWhen 2 or more codes are indicated, the lowest numbered code will appear first.
wIf a code not listed on the chart is displayed, the center airbag sensor assembly is faulty. RS±46
± SUPPLEMENTAL RESTRAINT SYSTEMTROUBLESHOOTING

DIAGNOSTIC TROUBLE CODE MATRIX CHART
If a malfunction code is displayed during the diagnostic trouble code check, check the circuit listed for that code
in the table below (Proceed to the page given for that circuit.).
 
 DTC No. 
 Diagnosis 
 Page
 (Normal)*1 
Source voltage drop RS±52
 
 
 
11
 
 
 

Short in squib circuit or front airbag sensor circuit (to ground)


Front airbag sensor or center airbag sensor assembly malfunction
 
 
 
RS±54
 
 
 
12 
 
 

Short in squib circuit (to B+)


Open in front airbag sensor circuits
 
 
 
RS±60
 13 
Short in D squib circuit (between D+ wire harness and D± wire harness) RS±66
 
 14
 
 
Open in D squib circuit
 
 RS±73
 
 15
 
 
Open in front airbag sensor circuit
 
 RS±78
 
 22*2 
 
SRS warning light system malfunction 
 RS±82
 31 
Center airbag sensor assembly malfunction RS±86
 
 53
 
 
Short in P squib circuit
 
 RS±87
 
 54
 
 
Open in P squib circuit
 
 RS±92
HINT:
*1 When the SRS warning light remains lit up and the diagnostic trouble code is the normal code, this means
a source voltage drop.
*
2 Code 22 is recorded when a malfunction occurs in the SRS warning light system.
If an open malfunction occurs in the SRS warning light system, the SRS warning light does not light up, so
that until the malfunction is repaired, the diagnostic trouble codes (including code 22) cannot be confirmed.
PROBLEM SYMPTOM CHART
Proceed with troubleshooting of each circuit in the table below.
RS±96
RS±98
Problem SymptomInspection ItemPage

Tc terminal circuit

SRS warning light system
Always lit up, when ignition
switch is in LOCK position.

With the ignition switch at ACC or ON, the SRS warning light
sometimes lights up after approx. 6 seconds have elapsed.

SRS warning light is always lit up even when ignition switch
is in the LOCK position.

Diagnostic trouble code not displayed.

SRS warning light is always lit up with the DTC check procedure.

Diagnostic trouble code displayed without Tc and E1 terminal
correction.
RS±50± SUPPLEMENTAL RESTRAINT SYSTEMTROUBLESHOOTING

CIRCUIT INSPECTION
DTC (Normal) Source Voltage Drop
CIRCUIT DESCRIPTION
The SRS is equipped with a voltage±increase circuit (DC±DC converter) in the center airbag sensor assembly
in case the source voltage drops.
When the battery voltage drops, the voltage±increase circuit (DC±DC converter) functions to increase the volt-
age of the SRS to normal voltage.
The diagnostic system malfunction display for this circuit is different to other circuits±when the SRS warning light
remains lit up and the diagnostic trouble code is a normal code, voltage source drop is indicated.
Malfunction in this circuit is not recorded in the center airbag sensor assembly, and the voltage source returns
to normal, after approx. 10 seconds the SRS warning light automatically goes off.
 DTC No. Diagnosis 
 (Normal)
 
 Voltage source drop.
RS±52± SUPPLEMENTAL RESTRAINT SYSTEMTROUBLESHOOTING

DTC 15 Open in Front Airbag Sensor Circuit
CIRCUIT DESCRIPTION
The front airbag sensor detects the deceleration force in a frontal collision and is located in the front fender on
the left and right sides.
For details of the function of each component, see FUNCTION OF COMPONENTS on page RS±4. Diagnostic
trouble code 15 is recorded when an open is detected in the front airbag sensor circuit.
NOTICE: The front airbag sensor connector is equipped with an electrical connection check mechanism
for the purpose of detecting an open in the front airbag sensor (See page RS±36). This mechanism is
constructed so that when the terminals of the front airbag sensor have been connected (when the con-
nector housing lock is in the locked condition), the connection detection pin on the wire harness side
connects with the terminals for diagnosis use on the sensor side. If the connector is not properly con-
nected, the diagnostic system may detect only a malfunction code, even though the SRS is functioning
normally.
When connecting the front airbag sensor connector, make sure it is connected properly. If diagnostic
trouble code 15 is displayed after the front airbag sensor connector has been connected, check again
that it is properly connected.
 DTC No. Diagnosis
 
 
 
 
15
 
 
 
 

Open circuit in + S wire harness or ± S wire harness of front airbag sensor.


Front airbag sensor malfunction.


Malfunction of electrical connection check mechanism of front airbag sensor.


Center airbag sensor assembly malfunction.
RS±78± SUPPLEMENTAL RESTRAINT SYSTEMTROUBLESHOOTING

DTC 22 SRS Warning Light System Malfunction
CIRCUIT DESCRIPTION
The SRS warning light is located on the cluster finish panel.
When the SRS is normal, the SRS warning light lights up for approx. 6 seconds after the ignition switch is turned
from LOCK position to ACC or ON position, and then turns off automatically.
If there is a malfunction in the SRS, the SRS warning light lights up to inform the driver of the abnormality. When
terminals Tc and E
1 of the DLC1 or DLC2 are connected, the diagnostic trouble code is displayed by the blinking
of the SRS warning light.
The SRS warning light circuit is equipped with an electrical connection check mechanism which detects when
the connector to the center airbag sensor assembly is not properly connected.
If the connector to the center airbag sensor assembly is not properly connected, the SRS warning light will not
light up.
Diagnostic trouble code 22 is recorded when a malfunction occurs in the SRS warning light system. If an OPEN
malfunction occurs in the SRS warning light system, the SRS warning light does not light up, so that until the
malfunction is repaired, the diagnostic trouble codes (including code 22) cannot be confirmed.
 
DTC No. 
Diagnosis 
 
 
22
 
 
 

Open circuit in SRS warning light system.


Center airbag sensor assembly malfunction.
RS±82± SUPPLEMENTAL RESTRAINT SYSTEMTROUBLESHOOTING