Lexus SC300 / Lexus SC400. Manual - part 665

CIRCUIT INSPECTION

Diag. Code  12

RPM Signal Circuit (No.1)

CIRCUIT DESCRIPTION

Cam position sensors (G1 and G2 signals) and engine speed sensor (NE signal) consist of a signal plate
and a pick up coil.
The G1, G2 signal plates have one tooth each on its outer circumference and are mounted on the left and
right bank camshafts.
When the camshafts rotate, the protrusion on the signal plate and the air gap on the pick up coil change,
causing fluctuations in the magnetic field and generating an electromotive force in the pick up coil.
The NE signal plate has 12 teeth and is mounted on the crankshaft. The NE signal sensor generates 12
NE signals per engine revolution. The ECU detects the standard crankshaft angle based on the G1, G2
signals, and the actual crankshaft angle and the engine speed by the NE signals.

Code No.

Diagnostic Code Detecting Condition

Trouble Area

•

Open or short in engine speed sensor, No. 1,

•

O en or short in engine s eed sensor, No. 1,
No. 2 cam position sensor circuit

12

No ”NE” or ”G1” and ”G2” signal to ECU

No. 2 cam  osition sensor circuit

•

Engine speed sensor

12

No  NE  or  G1  and  G2  signal to ECU
within 2 sec. after cranking.

•

Engine s eed sensor

•

No. 1, No. 2 cam position sensor

g

No. 1, No. 2 cam  osition sensor

•

Starter

•

ECU

TR–48

–

ENGINE TROUBLESHOOTING

Circuit Inspection

DIAGNOSTIC CHART

WIRING DIAGRAM

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–49

OK

NG

INSPECTION PROCEDURE

1

Check engine speed sensor, No. 1, No. 2 cam position sensor

C

OK

P

For engine speed sensor.

(2) Remove engine under cover.

(2) Disconnected engine speed sensor connector.

For No.1, No. 2 cam position sensor,

(2) Disconnect No. 1, No. 2 cam poisition sensor con-

nectors.

Measure resistance of engine speed sencor, No. 1 and
No. 2 cam position sensor.

Replace engine speed sensor, No. 1, No. 2 cam poistion
sensor.

TR–50

–

ENGINE TROUBLESHOOTING

Circuit Inspection

OK

NG

OK

NG

2

Check for open and short in harness and connector between engine & ECT ECU and each sen-
sor (See page 

IN–27

).

Repair or replace harness or connector.

3

Inspect sensor installation and teeth of signal plate.

Tighen the sensor.
Replace signal plate.

Check and replace engine and ECT ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–51