TOYOTA SUPRA 1995 Service Repair Manual

DTC 47 48 Sub±Throttle Position Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the opening angle of the sub±throttle valve and sends the appropriate signals to the ECU.
If a trouble signal is input, the ECU prohibits TRAC control.
 
 DTC No. 
 Diagnostic Trouble Code Detecting Condition 
 Trouble area
 
 
 
 
 
 
 
 
47
 
 
 
 
 
 
 
 
When any of the following (1) through (3) is
detected:
(1) Deviation of 5 steps or more to the closed side of
the idle step during sub±throttle initial check.
(2) Voltage at terminal IDL2 does not
become 0 V even after sub±throttle is driven to fully
closed position during sub±throttle initial check.
(3) Voltage at terminal VTA2 of ECM is 1.5 V or more
for at least 0.31 sec. while CTP switch is ON. 
 
 
 
 
 
 
 

Sub±throttle position sensor

Open or short in IDL2 circuit

ECM

TRAC ECU
 
 
 
 
 
 
48
 
 
 
 
 
 
Either of the following (1) or (2) continues for
at least 0.26 sec.:
(1) Input voltage of ECM terminal VTA2:
4.9 V or more
(2) Input voltage of ECM terminal VTA2:
0.1 V or less. 
 
 
 
 
 

Sub±throttle position sensor

Open or short in VTA2 circuit

ECM
BR±152± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

INSPECTION PROCEDURE
HINT: The sub±throttle position sensor signal is transmitted to the TRAC ECU from ECM, so if an error occurs
at the engine side, the TRAC ECU also detects it.
If diagnostic trouble code No. 47 is being output for the engine, troubleshoot the engine first.
Check voltage between terminal IDL2 of TRAC ECU and body ground.
Remove TRAC ECU with connectors still con-
nected.
Remove intake air duct.
Disconnect step motor connector.
Repair circuit indicated by the code output.
Do diagnostic trouble code check on page EG±491.
Is diagnostic trouble code output for the engine?
Turn ignition switch ON.
Measure voltage between terminal IDL2 of TRAC ECU
and body ground, when the sub±throttle valve is fully
closed and fully open.
Go to step 6.
Engine condition
Sub±throttle valve position
Fully open
Voltage
Below 1.0 V
10 ± 14 V
Fully closed
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±153

(See page IN±30).
(See page IN±30).
(See page IN±30).
(See page EG±294).
Check for open and short in harness and connector between terminal IDL2
of TRAC ECU and main throttle position sensor with TRAC ECU, ECM and
main throttle position sensor connectors disconnected (See page IN±30).
Check voltage of terminal VTA2 of ECM (See page EG±554).
Repair or replace harness or connector.
Check for short in harness between terminal IDL2 of TRAC ECU and body
ground with only main throttle position sensor connector connected (See
page IN±30).
Check and replace main throttle position sensor.
Check and replace ECM.
Check and replace TRAC ECU.
Check for short in harness between terminal IDL2 of TRAC ECU and body
ground with only ECM connector connected (See page IN±30).
Check for open and short in harness and connector between terminal
VTA2 of ECM and main throttle position sensor (See page IN±30).
Check main throttle position sensor (See page EG±555).
Check and replace ECM.
Repair or replace harness or connector.
Adjust or replace main throttle position sensor
See page EG±294).
Check and replace ECM.
BR±154± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

Check the diagnostic trouble code for the engine (See page EG±491).
Check for short in all the harness and ECU connected to malfunction indicator light.
Repair engine control system according to
the code output.Malfunction indicator
light remains ON.Output
NG code
DTC 51 Engine Malfunction Detection Circuit
CIRCUIT DESCRIPTION
If trouble in the engine control system causes the malfunction indicator light to light up, this information is trans-
mitted from the ECM to the TRAC ECU. The TRAC ECU may prohibit TRAC control as a result.
 
DTC No. 
Diagnostic Trouble Code Detecting Condition 
Trouble area 
 
 
 

51
 
 
 
 

Conditions (1) and (2) continue for more than
1 sec.:
(1) Engine speed: 500 rpm or more
(2) Malfunction information is input from the ECM.
 
 
 
 


Engine control system
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±155

(See page IN±30).
Check for open and short n harness and connector between terminals
EFI+, EFI±, TRAC+ and TRC± of ECU and ECM (See page IN±30).
When the TRAC indicator light is ON, there is a problem in the EFI + circuit, and when the TRAC in-
dictor light is OFF, there is a problem in the TRC + circuit.
Repair or replace harness or connector.
Check and replace ECM or TRAC ECU.
INSPECTION PROCEDURE
DTC 53 ECM Communication Circuit Malfunction
CIRCUIT DESCRIPTION
This circuit is used to send TRAC control information from the TRAC ECU to the ECM (TRC+, TRC±), and engine
control information from the ECM to the TRAC ECU (EFI+, EFI±).
 DTC No. Diagnostic Trouble Code Detecting Condition Trouble area
 
 
 
 
 
 
 
 
53
 
 
 
 
 
 
 
 
Either of the following (1) or (2) continues for
5 sec.:
(1) A signal is received from the ECM indicating
trouble in the TRC+ or TRC±
circuit.
(2) No EFI + data is received from the ECM
when the engine speed is 500 RPM or
more, or the vehicle speed is 60 km/h
(37 mph) or more. 
 
 
 
 
 
 
 

Open or short in TRC+ or TRC± circuit

Open or short in EFI+ or EFI± circuit

ECM

TRAC ECU
BR±156± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

DTC 61 ABS & TRAC ECU Communication Circuit Malfunction
CIRCUIT DESCRIPTION
 DTC No. Diagnostic Trouble Code Detecting Condition Trouble area
 
 
 61
 
 
 
Malfunction in ABS & TRAC ECU communication
circuit.
 
 
 

Open or short in ABSO, BRC, BRP circuit

ABS & TRAC ECU

TRAC ECU
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±157

INSPECTION PROCEDURE
(See page IN±30).
Check for open and short n harness and connector between terminals
EFI+, EFI±, TRAC+ and TRC± of ECU and ECM (See page IN±30).
Check and replace TRAC ECU.
Check and replace TRAC ECU.
Repair or replace harness or connector.
Check and replace ABS & TRAC ECU.
Check voltage between terminals ABSO, BRC, BRP of TRAC ECU and
body ground with TRAC ECU connector disconnected.
Check for open and short in harness and connector between ABS & TRAC
ECU and TRAC ECU (See page IN±30).
Remove TRAC ECU with connectors still con-
nected.
Measure voltage between terminals ABSO, BRC,
BRP of TRAC ECU and body ground when ignition
switch is turned ON.
Voltage:
ABSO, BRC: 6 Ð 14 V
BRP: About 7 V (Pulse)
Disconnect TRAC ECU connector.
Measure voltage between terminals ABSO, BRC,
BRP of TRAC ECU and body ground when ignition
switch is turned ON.
Voltage: See step 1. BR±158
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

TRAC OFF Indicator TRAC Cut Switch Circuit
CIRCUIT DESCRIPTION
This is the TRAC control main switch. When the TRAC cut switch is pushed on, TRAC control goes off and the
TRAC OFF indicator lights up. This indicator is also used for warnings when the trouble occurs.
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±159

page BR±126.
page BR±43.
(See page IN±30).
Is diagnostic trouble code output?
Check for open and short in harness and connector between terminal CSW
of TRAC ECU and TRAC cut switch and body ground (See page IN±30).
1. Remove TRAC cut switch.
2. Disconnect TRAC cut switch connector.
Measure resistance between terminals 1 and 2 of
TRAC cut switch when TRAC cut switch is on and
off.
Do diagnostic trouble code check on page BR 126.
Repair circuit indicated by the code output.
Replace TRAC cut switch.
Repair or replace harness or connector.
Check TRAC OFF indicator light.
See Combination Meter Troubleshooting on page BR±43.
Check TRAC cut switch.
TRAC car switch
Pushed in
Released
Continuity
1 M
or higher
Resistance
INSPECTION PROCEDURE
BR±160± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

Check TRAC solenoid relay.
Remove solenoid relay from R/B No.5.
Check continuity between each terminal of TRAC
solenoid relay shown below.
Repair or replace harness or connector.
Check and replace TRAC ECU.
Replace TRAC solenoid relay.
Apply battery positive voltage between termi-
nals 4 and 6
.
Check continuity between each terminal of
TRAC solenoid relay shown below.
Terminals 4 and 6
Terminals 2 and 3
Terminals 1 and 3
Continuity
Open
Continuity
(Reference value 80
)
Check for open and short in harness and connector between terminal WT
of TRAC ECU and battery or TRAC solenoid relay (See page IN±30).
Connect the
test lead to terminal 5 and the 
lead to terminal 3. Check continuity between the
terminals.
Continuity
If there is no continuity, connect the
 test lead to
terminal 5 and the

lead to terminal 3. Recheck
continuity between terminals.
Terminals 2 and 3
Terminals 1 and 3Continuity
Open
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±161