Lexus SC300 / Lexus SC400. Manual — part 846

DIAGNOSIS SYSTEM

DESCRIPTION

The ECU contains a built–in self–diagnosis system by which
troubles with the engine signal network are detected and a
”CHECK” 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 ”CHECK”

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
”CHECK” 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 ”CHECK” 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 ”CHECK” 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

–

ENGINE TROUBLESHOOTING

Diagnosis System

Diagnosis Inspection (Normal Mode)
”CHECK” ENGINE WARNING LIGHT
CHECK

1.

The ”CHECK” engine warning light will come on when the
ignition switch is turned ON and the engine is not running.
HINT: If the ”CHECK” 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 ”CHECK” 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 TDCL
or check connector.
SST 09843–18020

3. Read the diagnostic code from ”CHECK” 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.

–

ENGINE TROUBLESHOOTING

Diagnosis System

TR–11

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 IDL

points 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:

•

To confirm that the test mode is operating, check that the
”CHECK” engine warning light flashes when the ignition
switch is turned to ON.

•

If the ”CHECK” engine warning light does not flash,
proceed to troubleshooting 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 ”CHECK” 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:

•

The test mode will not start if terminals TE2 and E1 are
connected after the ignition switch is turned on.

•

When the engine is not cranked, diag. codes ”43”
(Starter signal) output, but this is not abnormal.

•

When the automatic transmission shift lever is in the ”D”,
”2”, ”L” or ”R” shift position, or when the air conditioner
is on or when the accelerator pedal is depressed, code
”51” (Switch condition signal) is output, but this is not
abnormal.

TR–12

–

ENGINE TROUBLESHOOTING

Diagnosis System

DIAGNOSTIC CODE CLEARANCE

1.

After repair of the trouble areas, the diagnostic code retained
in the ECU memory must be cleared out by removing the EFI
fuse (30A) from R/B No. 2 for 10 seconds or more, with the
ignition switch OFF.
HINT:

•

Cancellation can also be done by removing the battery
negative (–) terminal, but in this case, other memory
systems (clock, etc.) will also be cancelled out.

•

If it is necessary to work on engine components
requiring removal of the battery terminal, a check must
first be made to see if a diagnostic code has been
recorded.

2. After

cancellation,

road test the vehicle to check that a normal

code is now read on the ”CHECK” engine warning light.
If the same diagnostic code appears, it indicates that the
trouble area has not been repaired thoroughly.

–

ENGINE TROUBLESHOOTING

Diagnosis System

TR–13