Lexus SC300 / Lexus SC400. Manual — part 913

Disconnect distributor connector.

Measure resistance between each terminal shown in
table below.

Check resistance of each picup coils in distributor.

During cranking or idling, check between terminals G1,
G2, NE and G

of engine (&ECT) ECU.

HINT:

The correct waveforms appears as shown in the
illustration on the left.

Replace distributor.

Check for open and short in harness and connector between engine
(&ECT) ECU and distributor (See page

IN–27

Repair or replace harness or connector.

INSPECTION PROCEDURE

TR–48

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ENGINE TROUBLESHOOTING

Circuit Inspection

Remove distributor cap & rotor.

Using SST (G1 and G2 pickups) and a thikness gauge
(NE pickup). measure the air gap between the signal
rotor projection and pickup coil.
SST 09240–00020 fro G1 and G2 pickups

Air gap: 0.2–0.4 mm (0.008–0.016 in.)

Replace distributor.

Check and replace engine (& ECT) ECU.

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ENGINE TROUBLESHOOTING

Circuit Inspection

TR–49

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

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ENGINE TROUBLESHOOTING

Circuit Inspection

DIAGNOSTIC CHART

WIRING DIAGRAM

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ENGINE TROUBLESHOOTING

Circuit Inspection

TR–49