TOYOTA SUPRA 1995 Service Repair Manual

DTC 41 IG Power Source Circuit
CIRCUIT DESCRIPTION
This is the power source for the ECU, hence the CPU and the actuators.
 DTC No. Diagnostic Trouble Code Detecting Condition Trouble area
 
 
 
 
 
 
 
41
 
 
 
 
 
 
 
When either of the following (1) or (2) is
detected:
(1) Voltage at ECU terminal IG1 is less than
9.5 V for more than 10 sec. while engine
speed is 500 RPM or higher.
(2) Voltage at ECU terminal IG1 is more than
17 V for more than 5 sec.
 
 
 
 
 
 
 

Battery

IC regulator

Open or short in power source circuit

ECU
BR±142± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

INSPECTION PROCEDURE
Check battery positive voltage.
Voltage: 10 ± 14 V
Check and repair the charging system.
Remove TRAC ECU with connectors still
connected.
Turn ignition switch ON.
Measure voltage between terminals IG1 and
GND of TRAC ECU connector.
Voltage: 10 ± 14 V
Check voltage between terminals IG1 and GND of TRAC ECU connector.
Check and replace TRAC ECU.
Measure resistance between terminal GND of
TRAC ECU connector and body ground.
Resistance: 1
or less
Check continuity between terminal GND of TRAC ECU connector and
body ground.
Repair or replace harness or connector.
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±143

(See page IN±30).
Remove ECU±IG fuse from J/B No. 1.
Check continuity of ECU±IG fuse.
Continuity
Check ECU±IG fuse.
Check for short in all the harness and components
connected to ECU±IG fuse.
Check for open in harness and connector between
TRAC ECU and battery (See page IN±30).
BR±144± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

DTC 43 ABS & TRAC ECU Malfunction
CIRCUIT DESCRIPTION
 DTC No. Diagnostic Trouble Code Detecting Condition Trouble area
 



43
 
 
 
ABS control system or TRAC (BRAKE) control system
or communication circuit is abnormal.
 
 
 

ABS & TRAC ECU

Open or short in BRFA circuit
page BR±128.
Is diagnostic trouble code output for the ABS & TRAC (BRAKE)?
Perform diagnostic trouble code check on page BR±128.
Repair circuit indicated by the code
output.
INSPECTION PROCEDURE
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±145

Check voltage between terminal BRFA of TRAC ECU and body ground.
Remove TRAC ECU with connectors still con-
nected.
Turn ignition switch ON.
Measure voltage between terminal BRFA of TRAC
ECU and body ground.
Voltage: About 6 V (Pulse)
Check and replace TRAC ECU.
Check voltage between terminal BRFA of TRAC ECU and body ground with
TRAC ECU connector disconnected.
Disconnect TRAC ECU connector.
Measure voltage between terminal BRFA of TRAC
ECU connector and body ground.
HINT: Measure voltage within 8 seconds from the time
TRAC ECU connector is disconnected.
Voltage: See step 1.
Check and replace TRAC ECU.
Repair or replace harness or connector.
Check and replace ABS & TRAC ECU.
Check for open and short in harness and connector between ABS & TRAC
ECU and TRAC ECU (See page IN±30).
BR±146± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

DTC 44 NE Signal Circuit
CIRCUIT DESCRIPTION
The TRAC ECU receives engine speed signals (NE signals) from the ECM.
 DTC No. Diagnostic Trouble Code Detecting Condition Trouble area
 
 
 44
 
 
 
No signal is input to terminal NEO 0.24 sec.
after traction control is initiated.
 
 
 

Open or short in NEO circuit

ECM

TRAC ECU
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±147

(See page IN±30).
Check voltage between terminal NEO of TRAC ECU and body ground.
Remove TRAC ECU with connectors still con-
nected.
Repair or replace harness or connector.
Check and replace TRAC ECU or ECM.
Check for open and short in harness and connector between terminal NEO
of TRAC ECU and terminal NEO of ECM (See page IN±30).
Turn ignition switch ON.
Measure voltage between terminal NEO of TRAC
ECU and body ground for the engine conditions
below
If the same code is still output after the diagnostic code is deleted, check the contact condition of each
connection.
Engine condition
OFF (IG ON)
ON (Idling)
Voltage
4 ± 6 V or Below 1 V
2 ± 3 V (Pulse)
INSPECTION PROCEDURE
BR±148± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

DTC 45 46 Main Throttle Position Sensor Circuit
CIRCUIT DESCRIPTION
This circuit is not directly related to the TRAC control, but as it has an influence on TRAC control when trouble
occurs in this circuit, it is used to switch off the TRAC system as a fail safe function.
 
 DTC No. 
 Diagnostic Trouble Code Detecting Condition 
 Trouble area
 
 
 
 
45
 
 
 
 
Conditions (1) and (2) continue for 0.31 sec.:
(1) CTP switch of main throttle position sensor is ON.
(2) Input voltage of ECM terminal VTA1:
1.5 V or more. 
 
 
 

Main throttle position sensor

Short in IDL1 circuit

ECM

TRAC ECU
 
 
 
 
 
46
 
 
 
 
 
Either of the following (1) or (2) continues for
0.6 sec.:
(1) Input voltage of ECM terminal VTA1:
4.9 V or more.
(2) Input voltage of ECM terminal VTA1:
0.1 V or less. 
 
 
 
 

Main throttle position sensor

Open or short in VTA1 circuit

ECM
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±149

INSPECTION PROCEDURE
HINT: The main 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.41 is being output for the engine troubleshoot the engine first.
Remove TRAC ECU with connectors still con-
nected.
Disconnect the vacuum hose from the throttle
opener, and apply the vacuum to the throttle open-
er.
Is diagnostic trouble code output for the engine?
Turn ignition switch ON.
Measure voltage between terminal IDL1 of TRAC ECU
and body ground, when the main throttle valve is fully clo-
sed and fully open.
Main throttle valve position
Fully closed
Check voltage between terminal IDL1 of TRAC ECU and body ground.
Fully open
Voltage
Below 1.0 V
10 ± 14 V
Do diagnostic trouble code check on page EG±491.
Repair circuit indicated by the code output.
BR±150± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)

(See page IN±30).
page IN±30).
(See
(See page IN±30).
(See page EG±554).
Check for open and short in harness and connector between terminal IDL1
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 VTA1 of ECM (See page EG±554).
Repair or replace harness or connector.
Check for short in harness between terminal IDL1 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 IDL1 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
VTA1 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±292).
Check and replace ECM.
± BRAKE SYSTEMTRACTION CONTROL SYSTEM (TRAC)BR±151