1991 LEXUS SC400 light

CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed c\
onfirming that diag. code is nolonger detected.

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 3 min.
With the A/C ON and transmission in D range (O/D OFF), drive at 40±\
70 mph for 4 min.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light up at 1±4 min. of driving at 40±70 mph (64±112 km/h).
NOTICE: If the conditions in this test are not strictly followed, detection of the\
malfunction will not be possible.
Malfunction: Open in EGR gas temp. sensor circuit
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ENGINE TROUBLESHOOTING Circuit InspectionTR±109
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WIRING DIAGRAM
Diag. Code 78Fuel Pump Control Circuit
CIRCUIT DESCRIPTION
The fuel pump speed is controlled at two steps (high speed, low speed) by\
the condition of the engine (starting, light load,
heavy load), when the engine starts (STA ON), the engine (& ECT) ECU sends a Hi signal to the fuel pump ECU \
(FPC termi-
nal).
The fuel pump ECU then outputs Hi voltage (battery voltage) to the fue\
l pump so that the fuel pump operates at high speed.
After the engine starts, during idling or light loads, the engine (& ECT) EC\
U outputs a High Low signal to the fuel pump ECU,
the fuel pump ECU outputs Lo battery voltage (about 9V) to the fuel pu\
mp and causes the fuel pump to operate at low speed.
If the intake air volume increases (high engine load), the engine (& EC\
T) ECU sends a Hi signal to the fuel pump ECU and
causes the fuel pump to operate at high speed.
DTC No.
DTC Detecting ConditionTrouble Area
(1) Open or short in fuel pump circuit for 1 sec. or more with en- gine speed 1,000 rpm or less.
(2 trip detection logic)*
Open or short in fuel pump ECU circuit.
78
(2) Open in input circuit of fuel pump ECU (FPC) with engine
speed 1,000 rpm or less.
(2 trip detection logic)*Fuel pump ECU
 Engine (& ECT) ECU power source circuit.
 Fuel pump
(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 (& ECT) ECU
*: See page TR±25.
TR±110±
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Diag. Code 78Fuel Pump Control Circuit
CIRCUIT DESCRIPTION
The fuel pump speed is controlled at two steps (high speed, low speed) by\
the condition of the engine (starting,
light load, heavy load), when the engine starts (STA ON), the engine & ECT ECU sends a Hi signal to the fuel
pump ECU (FPC terminal).
The fuel pump ECU then outputs Hi voltage (battery voltage) to the fuel p\
ump so that the fuel pump operates
at high speed.
After the engine starts, during idling or light loads, the engine & ECT ECU o\
utputs a High Low signal to the fuel
pump ECU, the fuel pump ECU outputs Lo battery voltage (about 9V) to the f\
uel pump and causes the fuel pump
to operate at low speed.
If the intake air volume increases (high engine load), the engine & ECT \
ECU sends a Hi signal to the fuel pump
ECU and causes the fuel pump to operate at high speed.
Code No.Diagnostic Code Detecting ConditionTrouble 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)*

Open or short in fuel pump ECU circuit.
78
(2) Open in input circuit of fuel pump ECU(FPC) with
engine speed 1,000 rpm or less.
(2 trip detection logic)*
Fuel pump ECU

Engine & ECT ECU power source circuit.

Fuel pump
(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)*

Fuel um

Engine & ECT ECU
*: See page TR±21.
WIRING DIAGRAM
TR±114±
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OKNG
OKNG
INSPECTION PROCEDURE
1Check output condition of diag. code 51.
C
OK
Hint
PSetting the test mode.
(2) Turn ignition switch OFF.
(2) Connect terminals TE2 and E1 and TDCL.
(2) Turn ignition switch ON.(For checking terminal A/C, start the engine.)
(2) Connect terminals TE1 and E1 of TDCL.
Check if code ª51º is output by the ªCHECKº engine
warning light.
*: Before the STA signal is input (ST is not ON), diagnostic code 43 is also output.
Diag. code 42 is output with vehicle speed 5 km/h (3
mph) or below
IDL1 .... Go to step 2 NSW ... Go to page TR±22.
A/C ..... Go to step 3
Proceed to next circuit inspection shown on
maxtrix chart (See page TR±35).
2Check throttle position sensor.
C
OK
PDisconnect throttle position sensor connector.
Measure resistance between terminals IDL1 and E2 of
throttle position sensor connector.
Adjust or replace throttle position sensor
See page FI±73).
Check and repair harness or connector between
engine & ECT ECU and throttle position sensor.
TR±120±
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TE1, TE2 Terminal Circuit
CIRCUIT DESCRIPTION
Terminal TE1 is located in the check connector in the engine compartment and terminals T\
E1 and TE2 are lo-
cated in the TDCL in the cabin. When these terminals are connected with \
the E1 terminal, diagnostic codes in
normal mode or test mode can be read from the ºCHECKº engine warning lig\
ht on the combination meter.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: If terminals TE1 and TE2 are connected with terminal E1, diagnostic code is not output or test mode isnot activated.
Even though terminal TE1 is not connected with terminal E1, the ºCHEC\
Kº engine warning light blinks.
For the above phenomenon, the likely cause is an open or short in the wire \
harness, or malfunction inside
the ECU.
Check continuity between terminal E1 and
body ground.
Repair or replace harness or
connector.Check for open and short in harness and
connector between check connector TDCL
and ECU.
Check voltage of terminals TE1, TE2.
Check and replace ECU.
Repair or replace harness or
connector.
Check and replace ECU.
WIRING DIAGRAM
TR±146±
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DIAGNOSIS SYSTEM
DESCRIPTION
The ECU contains a built±in self±diagnosis system by which
troubles with the engine signal network are detected and a
ºCHECKº engine warning light on the instrument panel lights up.
By analyzing various signals as shown in the later table (See page
TR±14) the Electronic Control Unit (ECU) detects system malfunc-
tions relating to the sensors or actuators.
In the normal mode, the self±diagnosis system monitors 22 (USA
specification vehicles with TRAC control) or 21 (USA (except for
California) and Canadian specification vehicles with TRAC con-
trol) items, indicated by code No. as shown in TR±14. A ºCHECKº
engine warning light informs the driver that a malfunction has been
detected. The light goes off automatically when the malfunction
has been repaired. But the diagnostic code(s) remains stored in
the ECU memory (except for code Nos. 16 and 53). The ECU
stores the code(s) until it is cleared by removing the EFI fuse with
the ignition switch off.
The diagnostic code can be read by the number of blinks of the
ºCHECKº engine warning light when TE1 and E1 terminals on the
TDCL or check connector are connected. When 2 or more codes
are indicated, the lowest number (code) will appear first.
In the test mode, 15 (USA specification vehicles with TRAC con-
trol) or 14 (USA (except for California) and Canadian specification
vehicles with TRAC control) items, indicated by code No. as
shown in TR±14 are monitored. If a malfunction is detected in any
one of the systems indicated by code Nos. 13, 21, 22, 24, 25, 26,
27, 28, 29, 35, 41, 42, 47, 71 and 78 (USA specification vehicles)
or 13, 21, 22, 24, 25, 26, 27, 28, 29, 35, 41, 42, 47 and 78 (USA
(except for California) and Canadian specification vehicles) the
ECU lights the ºCHECKº engine warning light to warn the techni-
cian that malfunction has been detected. In this case, TE2 and E1
terminals on the TDCL should be connected as shown later. (See
page TR±12 ).
In the test mode, even if the malfunction is corrected, the malfunc-
tion code is stored in the ECU memory even when the ignition
switch is off (except code Nos. 43 and 51). This also applies in the
normal mode. The diagnostic mode (normal or test) and the output
of the ºCHECKº engine warning light can be selected by connect-
ing the TE1, TE2 and E1 terminals on the check connector or
TDCL, as shown later.
A test mode function has been added to the functions of the self±
diagnosis system of the normal mode for the purpose of detecting
malfunctions such as poor contact, which are difficult to detect in
the normal mode. This function fills up the selfdiagnosis system.
The test mode can be implemented by the technician following the
appropriate procedures of check terminal connection and opera-
tion described later. (See page TR±12)
TR±10
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Diagnosis Inspection (Normal Mode)
ºCHECKº ENGINE WARNING LIGHT
CHECK
1. The ºCHECKº engine warning light will come on when theignition switch is turned ON and the engine is not running.
HINT: If the ºCHECKº engine warning light does not light up,
proceed to troubleshooting of the combination meter (See
page
BE±146).
2. When the engine is started, the ºCHECKº engine warning light should go off.
If the light remains on, the diagnosis system has detected a
malfunction or abnormality in the system.
DIAGNOSTIC CODE CHECK
1. Turn ignition switch on.
2. Using SST, connect terminals between TE1 and E1 of TDCLor check connector.
SST 09843±18020
3. Read the diagnostic code from ºCHECKº engine warning light.
HINT: If a diagnostic code is not output, check the TE1 termi-
nal circuit (See page TR±146).
As an example, the blinking patterns for codes;normal, 12
and 31 are as shown on the illustration.
4. Check the details of the malfunction using the diagnostic
code table on page TR±14.
5. After completing the check, disconnect terminals TE1 and E1, and turn off the display.
HINT: In the event of 2 or more malfunction codes, indication
will begin from the smaller numbered code and continue in
order to the larger.
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ENGINE TROUBLESHOOTING Diagnosis SystemTR±11
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Diagnosis Inspection (Test Mode)
Compared to the normal mode, the test mode has high sensing
ability to detect malfunctions.
It can also detect malfunctions in the starter signal circuit, the IDL
contact signal of the throttle position sensor, air conditioner signal
and neutral start switch signal.
Furthermore, the same diagnostic items which are detected in the
normal mode can also be detected in the test mode.
DIAGNOSTIC CODE CHECK
1. Initial conditions.(a) Battery voltage 11 V or more.
(b) Throttle valve fully closed (throttle position sensor IDLpoints closed).
(c) Transmission in neutral position.
(d) Air conditioner switched off.
2. Turn ignition switch off.
3. Using SST, connect terminals TE2 and E1 of TDCL. SST 09843±18020
4. Turn ignition switch on. HINT:
wTo confirm that the test mode is operating, check that the
ºCHECKº engine warning light flashes when the ignition
switch is turned to ON.
w If the ºCHECKº engine warning light does not flash,
proceed to tro ubleshooting of the TE2 terminal circuit on
page TR±146 .
5. Start the engine.
6. Simulate the conditions of the malfunction described by the customer.
7. After the road test, using SST, connect terminals TE1 and E1
of TDCL or check connector.
SST 09843±18020
8. Read the diagnostic code on ºCHECKº engine warning light on the combination meter (See page TR±11).
9. After completing the check, disconnect terminals TE1, TE2 and E1, and turn off the display.
HINT:
wThe test mode will not start if terminals TE2 and E1 are
connected after the ignition switch is turned on.
w When the engine is not cranked, diag. codes º43º
(Starter signal) output, but this is not abnormal.
w When the automatic transmission shift lever is in the ºDº,
º2º, ºLº or ºRº shift position, or when the air conditioner
is on or when the accelerator pedal is depressed, code
º51º (Switch condition signal) is output, but this is not
abnormal.
TR±12
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