Lexus SC300 / Lexus SC400. Manual - part 679

DIAGNOSTIC CHART

HINT: 

If diag. code 52 is displayed, check No. 1 knock sensor (for left bank) circuit.

If diag. code 55 is displayed, check No. 2 knock sensor (for right bank) circuit.
If diag. code 53 is displayed, replace engine & ECT ECU.

Does malfunction disappear when a good knock
sensor is installed?

Repair or replace harness or
connector.

Replace knock sensor.

Check no continuity of knock sensor circuit.

Check knock sensor.

Check for open and short in harness and
connector between knock sensor and ECU.

Replace knock sensor.

Check and replace ECU.

WIRING DIAGRAM

TR–104

–

ENGINE TROUBLESHOOTING

Circuit Inspection

NG

OK

OK

NG

INSPECTION PROCEDURE

1

Check continuity between terminals KNK1, KNK2 of engine & ECT ECU connector and body
ground.

C

OK

P

(2) Connect the Check Harness A.

(See page 

TR–30

)

(2) Disconnect the engine & ECT ECU connector.

Measure resistance between terminals KNK1, KNK2 of
engine & ECT ECU connector and body ground.

Resistance:

1 M

 or higher

Go to step 3.

2

Check knock sensor.

C

OK

P

Disconnect knock sensor connector.

Measure resistance between the knock sensor terminal
and body.

Resistance:

1 M

 or higher

Replace knock sensor (See page 

FI–108

).

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–105

OK

NG

NO

YES

3

Check for open and short in harness and connectors between engine & ECT ECU and knock

sensor (See page 

IN–27

)

Repair or replace harness or connector.

4

Does malfunction disappear when a good knock sensor is installed?

Replace knock sensor (See page 

FI–108

).

Check and replace engine & ECT ECU.

Reference  |   INSPECTION USING OSCILLOSCOPE

•

With the engine racing (4,000 rpm) measure
between terminals KNK1, KNK2 of engine & ECT
ECU and body ground.

HINT: The correct waveform appears as shown in the 

Illustration on the left.

•

Spread the time on the horizontal axis, and confirm
that period of the wave is 151 sec.
(Normal mode vibration frequency of knock sensor:
6.6 KHz).

HINT: If normal mode vibration frequency is not 6.6 KHz, the

sensor is malfunctioning.

TR–106

–

ENGINE TROUBLESHOOTING

Circuit Inspection

–MEMO–

ENGINE TROUBLESHOOTING

TR–107