Lexus SC300 / Lexus SC400. Manual - part 656

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

DIAGNOSTIC CODE CHART

HINT: Parameters listed in the chart may not be exactly same as your reading due to type of the instruments
or other factors.

*4: See page 

TR–21

.

TR–14

–

ENGINE TROUBLESHOOTING

Diagnostic Code Chart

If a malfunction code is displayed during the diagnostic code check in test mode, check the circuit for that code
listed in the table below (Proceed to the page given for that circuit).

Tro ble Area

”CHECK” Engine

Warning Light *

Memory*



See Page

Trouble Area

Normal

Mode

Test

Mode

–––––––––––––

–––

–––

–––––

–––––

•

Open or short in engine speed sensor, No. 1, No. 2
cam position sensor circuit.

•

Engine speed sensor

•

No. 1, No. 2 cam position sensor

•

Starter

•

ECU

ON

N.A.



TR–48

•

 Open or short in engine speed sensor circuit.

•

 O en or short in engine s eed sensor circuit.

•

 Engine speed sensor

ON

N.A.

 Engine s eed sensor

•

 ECU

ON

N.A.

•

 Open or short in engine speed sensor circuit.

g

•

 Mechanical system malfunction (skipping teeth of
ti i

timing

•

belt belt stretched)

N.A.

ON



TR 52

•

belt, belt stretched)

•

Engine speed sensor



TR–52

•

 Engine s eed sensor

•

 ECU

•

 Mechanical system malfunction (skipping teeth of

•

 Mechanical system malfunction (ski

ing teeth of

•

timing belt, belt stretched)

ON

N A

•

timing belt, belt stretched)

•

 No. 1, No. 2 cam position sensor

ON

N.A.

 No. 1, No. 2 cam  osition sensor

•

 ECU

•

 Open or short in IGF1 circuit from igniter No.
1–ECU.

•

 Igniter No. 1

•

 ECU

ON

N.A.



TR–54

•

 Open or short in IGF2 circuit from igniter No.
2–ECU.

•

 Igniter No. 2

•

 ECU

ON

N.A.



TR–54

•

 ECU

ON

N.A.

X

TR–61

•

 Open or short in heater circuit of main oxygen sen-
sor.

•

Main oxygen sensor heater

ON

N.A.

•

 Main oxygen sensor heater

•

 ECU



TR–62

•

 Main oxygen sensor circuit

•

Main oxygen sensor

ON

ON

•

 Main oxygen sensor

*1, 2: See page 

TR–20

.

–

ENGINE TROUBLESHOOTING

Diagnostic Code Chart

TR–15