1986 TOYOTA SUPRA Service Repair Manual

DTC 78 Fuel Pump Control Circuit
CIRCUIT DESCRIPTION
The fuel pump speed is controlled at 2 steps (high speed, low speed) by the condition of the engine (starting,
light load, heavy load), when the engine starts (STA ON), the engine control module sends a Hi signal (battery
positive voltage) to the fuel pump ECU (FPC terminal).
The fuel pump ECU then outputs Hi voltage (battery positive voltage) to the fuel pump so that the fuel pump
operates at high speed.
After the engine starts, during idling or light loads, the engine control module outputs a Low signal (about 9 V)
to the fuel pump ECU, the fuel pump ECU outputs Low battery voltage (about 9 V) to the fuel pump and causes
the fuel pump to operate at low speed.
If the intake air volume increases (high engine load), the engine control module sends a Hi signal to the fuel
pump ECU and causes the fuel pump to operate at high speed.
 
 DTC No.
 
 Diagnostic Trouble Code Detecting Condition
 
 Trouble Area
 
 
 
 
 
 
 
 
(1) Open or short in fuel pump circuit for
1 sec. Or more with engine speed
1,000 rpm or less
(2 trip detection logic)* 
 
 
 O h t i f l ECU i it 
 
 
78
 
 
 
(2) Open in input circuit of fuel pump ECU
(FPC) with engine speed 1,000 rpm or
less
(2 trip detection logic)* 
 
 

Open or short in fuel pump ECU circuit

Fuel pump ECU

Engine control module power source circuit

Fuel pump

Engine control module 
 
 
 
 
 
 
 
(3) Open or short in diagnostic signal line (DI)
of fuel pump ECU with engine speed
1,000 rpm or less
(2 trip detection logic)*
 
 
 
 

Engine control module
*: See page EG±503. EG±568
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

(See page IN±30).
Check for ECM power source circuit (See page
EG±576), and check for open in harness and
connector between terminal +B of data link
connector 1 and main relay.
(1) Turn ignition switch ON.
(2) Using SST, connect terminals +B and FP of data
link connector 1.
SST 09843±18020
Check that there is pressure in the hose from the fuel
filter.
Fuel pressure can be felt.
Check fuel pump operation.
Repair or replace harness or connector.
Check for open and short in harness and connector between terminals
+B
+B, FP
FP of the data link connector 1 and fuel pump ECU (See
page IN±30).
Turn ignition switch ON.
Measure voltage between terminal +B of data link con-
nector 1 and body ground.
Voltage: 9 Ð 14 V
Check voltage of terminal +B of data link connector 1.
Check for ECM power source circuit (See
page EG±576), and check for open in harness
and connector between terminal +B of data
link connector 1 and main relay.
INSPECTION PROCEDURE
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±569

(See page IN±30).
(See page IN±30).(See page IN±30).
(See page EG±323)
(See page IN±30).
(1) Remove the LH quarter trim panel.
(See page EG±323)
(2) Disconnect fuel pump ECU connector.
Measure voltage between terminals 5 (FPC) and 8 (E)
of fuel pump ECU connector when igintion switch is
turned to START.
Voltage: 4.5 Ð 5.5 V
Check voltage between terminals 5 (FPC) and 8 (E) of fuel pump ECU con-
nector.
Check for open and short in harness and connector between terminal DI of
engine control module and terminal 6 (DI) of fuel pump ECU
(See page IN±30).
Check for open and short in harness and connector between terminal FP of
data link connector 1, fuel pump and body ground)See page IN±30).
Repair or replace fuel pump.
Repair or replace harness or connector.
Replace fuel pump ECU.
Check for open in harness and connector between terminal FPC of engine
control module and terminal 5 (FPC) of fuel pump ECU, terminal 8 (E) of fuel
pump ECU and body ground (See page IN±30).
Repair or replace harness or connector.
Repair or replace harness or connector.
Check and replace engine control module.
EG±570± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

DTC 51 Switch Condition Signal Circuit
CIRCUIT DESCRIPTION
Park/Neutral Position Switch
The ECM uses the signals from the park/neutral position switch to determine whether the transmission is in park
or neutral, or in some other position.
Air Conditioning Switch Signal
The ECM uses the output from the air conditioning switch to determine whether or not the air conditioning is
operating so that it can increase the idling speed of the engine if necessary.
Throttle Position Sensor IDL Signal
The IDL contacts are mounted in the throttle position sensor, and detects the idle condition.
 DTC No. Diagnostic Trouble Code Detecting Condition Trouble Area
 
 
 
 
 
 
51
 
 
 
 
 
 
(1) 3 sec. or more after engine starts with
closed throttle position switch OFF
(IDL1)
(2) Park/neutral position switch: OFF
(Shift position in ºRº, ºDº, º2º or º1º
position.)
(3) A/C switch ON 
 
 
 
 
 

Throttle position sensor IDL circuit

Accelerator pedal and cable

Park/neutral position switch

A/C switch circuit

ECM
HINT: In this circuit, diagnosis can only be made in the test mode.
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±571

INSPECTION PROCEDURE
PNP...Go to page EG±574.
(See page EG±514).
Setting the test mode.
(1) Turn ignition switch OFF.
(2) Connect terminals TE2 and E1 of DLC2.
(3) Turn ignition switch ON.
(For checking terminal IDL, disconnect the
vacuum hose from the throttle body, then ap-
ply vacuum to the throttle opener (See page
EG±292)).
((For checking terminal A/C, start the engine.)
(4) connect terminals TE1 and E1 of DLC2.
Check if code ª51º is output by the malfunction indi-
cator lamp.
*: Before the STA signal is input (ST is not ON), diag±
nostic trouble code 43 is also output.
Diagnostic trouble code 42 is output with vehicle speed
5 km/h (3 mph) or below.
Check output condition of diagnostic trouble code 51.
IDL1...Go to step [2].
PNP....Go to page Eg±574.
A/C....Go to step [3].
Proceed to next circuit inspection shown on matrix
chart (See page Eg±514).
Check output condition of diagnostic trouble code 51.
Throttle Position
Sensor (IDL1)
Condition
Park/Neutral Posi-
tion Switch (PNP)
Code
Accelerator pedal
released
Accelerator pedal
depressed
A/C SW ON
A/C SW OFFA/C Switch (A/C)
P or N position
R, D, 2 or L position
EG±572± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

(See page EG±292)
(See page EG±510)
(See page AC±62)
(1) Remove throttle body.
(See page EG 291)
(2) Apply vacuum to throttle opener.
(See page EG±292)
Measure resistance between terminals 3 (IDL1)
and 4 (E2) of throttle position sensor connector.
Check throttle position sensor.
Check voltage between terminal A/C of engine control module connector and
body ground.
Adjust or replace throttle position sensor.
(See page EG±292)
Check and repair harness or connector between en-
gine control module and throttle position sensor.
(1) Connect SST (check harness ªAº).
(See page EG±510)
SST 09990±01000
(2) Start the engine.
Measure voltage between terminal A/C of engine
control module and body ground.
Check A/C compressor circuit.
(See page EG±62)
Check and replace engine control module.
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±573

Park Neutral Position Switch Circuit
CIRCUIT DESCRIPTION
The park/neutral position switch goes on when the shift lever is in the N or P shift position. When it goes on the
terminal NSW of the ECM is grounded to body ground via the starter relay and theft deterrent ECU, thus the
terminal NSW voltage becomes 0 V. When the shift lever is in the D, 2, L or R position, the park/neutral position
switch goes off, so the voltage of ECM terminal NSW becomes positive battery voltage, the voltage of the ECM
internal power source.
If the shift lever is moved from the N position to the D position, this signal is used for air±fuel ratio correction
and for idle speed control (estimated control), etc.
When the park/neutral position switch is off, code º51º is output in the test mode diagnosis. (This is not abnor-
mal.)
EG±574± ENGINE2JZ±GTE ENGINE TROUBLESHOOTING

INSPECTION PROCEDURE
HINT: This diagnosis chart is based on the premise that the engine is being cranked under normal conditions.
If the engine does not crank, proceed to the matrix chart of problem symptoms on page EG±514.
(See page EG±514).
(See page IN±30).
(See page AT2±101).
(1) Connect terminals TE2 and E1 of DLC2.
(2) Turn ignition switch ON.
(3) Crank the engine.
(4) Connect terminals TE1 and E1 of DLC2.
Check if diagnostic trouble code ª51º is output
when the shift lever is in the P and D shift positions.
Check output condition of diagnostic trouble code 51.
Check for open in harness and connector between engine control module
and park/neutral position switch (See page IN±30).
Check and replace engine control module.
Proceed to next circuit inspection shown on matrix
chart (See page EG±514).
Repair or replace harness or connector.
Replace park/neutral position switch.
Check and replace engine control module.
Check park/neutral position switch (See page AT2±101).
Shift
PositionResult
NG Type ING Type II
Normal CodeNormal Code
Normal CodeCode 51
Code 51
Code 51
''P''
''D''
OK
NG
Type I
NG
Type II
± ENGINE2JZ±GTE ENGINE TROUBLESHOOTINGEG±575