ECU LEXUS SC400 1991 Service Repair Manual

TERMINALS OF ECU (Cont'd)
*1: Only vehicles with ECT.
*2: Only for USA specification vehicles. TR±36
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ENGINE TROUBLESHOOTING Terminals of ECU
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STANDARD VALUE OF ECU TERMINALS
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ENGINE TROUBLESHOOTING Standard Value of ECU TerminalsTR±37
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STANDARD VALUE OF ECM TERMINALS
* Only for USA specification vehicles. TR±38
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ENGINE TROUBLESHOOTING Standard Value of ECU Terminals
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CIRCUIT INSPECTIONDiag. Code 12
RPM Signal Circuit (No. 1)
CIRCUIT DESCRIPTION
The distributor in the Engine Control System contains three pick±up coil\
s (G1, G2 and NE).
The G1, G2 signals inform the ECU of the standard crankshaft angle.
The NE signals inform the ECU of the crankshaft angle and the engine spe\
ed.
 Code No. Diagnostic Code Detecting Condition Trouble Area
  
NoºNEºorºG1ºandºG2ºsignal to ECU within 2
 

Open or short in NE G circuit  No ºNEº or ºG1º and ºG2º signal to ECU within 2
sec after cranking 
Open or short in NE, G circuit.

Distributor
 12 sec. after cranking. 
Distributor

Open or short in STA circuit.
ECU  Open in ºGº
circuit. 
Oen or short in STA circuit.

ECU
TR±46±
ENGINE TROUBLESHOOTING Circuit Inspection
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DIAGNOSTIC CHART
WIRING DIAGRAM
Check resistance of each pickup coils in
distributor
Check for open and short in harness and
connector between ECU and distributor.
Check air gap.
Check and replace ECU.
Replace distributor.
Repair or rep lace harness or connector.
Replace distributor
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±47
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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±
ENGINE TROUBLESHOOTING Circuit Inspection
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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 InspectionTR±49
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CIRCUIT INSPECTIONDiag. Code 12
RPM Signal Circuit (No.1)
CIRCUIT DESCRIPTION
Cam position sensors (G1 and G2 signals) and engine speed sensor (NE sig\
nal) 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 forc\
e in the pick up coil.
The NE signal plate has 12 teeth and is mounted on the crankshaft. The NE s\
ignal sensor generates 12
NE signals per engine revolution. The ECU detects the standard crankshaf\
t 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 ConditionTrouble Area
wOpen or short in engine speed sensor, No. 1,w Oen or short in engine s eed sensor, No. 1,
No. 2 cam position sensor circuit
12No ºNEº or ºG1º and ºG2º signal to ECU
No. 2 cam osition sensor circuit
w Engine speed sensor12No NE or G1 and G2 signal to ECU
within 2 sec. after cranking.
wEngine s eed sensor
wNo. 1, No. 2 cam position sensorgNo. 1, No. 2 cam osition sensor
wStarter
wECU
TR±48±
ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
OKNG
2Check for open and short in harness and connector between engine & ECT ECU an\
d each sen-
sor (See page IN±27).
Repair or replace harness or connector.
3Inspect sensor installation and teeth of signal plate.
Tighen the sensor.
Replace signal plate.
Check and replace engine and ECT ECU.
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ENGINE TROUBLESHOOTING Circuit InspectionTR±51
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Diag. Code 13RPM Signal Circuit (No. 2)
CIRCUIT DESCRIPTION
Refer to RPM signal circuit (No. 1) on page TR±46.
Code No.Diagnostic Code Detecting ConditionTrouble Area
13
No NE signal to ECU for 0.1 sec. or more at
1,000 rpm or more.

Open or short in NE circuit

Distributor13
No 12 pulses of NE to ECU during the interval

Distributor

ECU
No 12 ulses of NE to ECU during the interval
between G1 and G2 pulses.

ECU
DIAGNOSTIC CHART
This code indicates that a momentary interruption of the RPM signal from the\
distributor to the ECU has
occurred, but that it is returned to normal. Note that although this problem may \
not necessarily appear
at the time of inspection, it cannot be ignored because this diagnostic co\
de is output, indicating that there
is or was a malfunction in the RPM signal circuit; this ºmalfunctionº\
is usually a loose connector.
The distributor connector and the NE terminal of the ECU connector must the\
refore be checked for the
following:
1. Loose connectors
2. Dirty connector terminals
3. Loose connector terminals
TR±50±
ENGINE TROUBLESHOOTING Circuit Inspection
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