check engine LEXUS SC400 1991 Service Repair Manual

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BASIC INSPECTION
When the normal code is displayed in the diagnostic code check, troubleshoot\
ing should be performed in the
order for all possible circuits to be considered as the causes of the pr\
oblems.
In many cases, by carrying out the basic engine check shown in the follo\
wing flow chart, the location causing
the problem can be found quickly and ef ficiently. Therefore, use of this check is essential in engine troubleshoot-
ing.
1Is battery voltage 11 V or more when engine is stopped?
Charge or replace battery.
2Is engine cracnked?
Proceed to matrix to matrix chart of problem
symptoms on page TR±35.
3Does engine start?
Go to step [7]
4Check air filter
C
Hint
PRemove air filter
Visially check that the air cleaner element is not exces-
sively damaged or oily.
If necessary, clean element with compressed air. First
blow from inside thoroughly, then blow off outside of ele-
ment.
Repair or replace
Go to Step [5].
TR±24±
ENGINE TROUBLESHOOTING Basic Inspection
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5Check idle speed.
C
OK
P(1) Warm up engine at normal operating temperature.
(2) Switched off all accessories.
(3) Switched off air conditioner.
(4) Shift transmission into ªNº range.
(5) Connect tachometer test probe to terminal IG
of
check connector, and set the tachometer to the
4±cylinder range.
Check idle speed.
Idle speed: 650 ~ 750 rpm
Caution:

NEVER allow tachometer test probe to touch
ground as it could result in damage to igniter
and/or coil.

As some tachometers are not compatible with
this ignition system, we recommended that you
confirm compatibility of your unit before use.
Proceed to matrix chart of problem symptoms on page
TR±35 .
6Check ignition timing.
C
OK
P(1) Warm up engine at normal operating temperture.
(2) Shift transmission into ªNº range.
(3) Keep the engine speed at idle.
(4) Using SST, connect terminals TE1 and E1 of check
connector.
SST 09843±18020
(5) Using a timing light. connect the tester to No. 6 high±tension cord.
Check ignition timing.
Ignition Timing: 8±12  BTDC at idle
Proceed to page IG±28 and continue to troubleshoot.
Proceed to matix chart of problem symptoms on
page TR±35 .
±
ENGINE TROUBLESHOOTING Basic InspectionTR±25
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OKNG
OKNG
7Check fuel pressure.
C
P(1) Be sure that fuel is enough in tank.
(2) Turn ignition switch on.
(3) Using SST, connect terminals FP and + B of checkconnector.
SST 09843±18020
Check that pulsation damper screw rises up when termi-
nals are connected.
Caution:
Never make a mistake with the terminal connection
position as this will cause a malfunction.
Proceed to page FI±18 and continue to troubleshoot.
8Check for spark.
C
Hint
Disconnect the high±tension cord from the distributor
and, hold the end about 12.5 mm (1/2º) from the ground,
see if spark occurs while the engine is being cranked.
To prevent excessive fuel injected from the injectors dur-
ing this test, Don't crank the engine for more than 1 ± 2
seconds at a time.
Proceed to the page IG±6 and continue to troubleshoot.
Proceed to matix chart of problem systems on
page TR±35 .
TR±26±
ENGINE TROUBLESHOOTING Basic Inspection
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TERMINALS OF ECU
Connectors of the engine & ECT ECU are water±proof and are the
bolt type.
For water proof type connectors, in order to measure the voltage
of ECU terminals and the resistance of connected parts, connect
the inspection sub wire harness between the ECU and vehicle
wire harness, then perform the inspection. The inspection method
of inserting a tester probe from the other side of connector notice-
ably reduces the water±proof ability.
Disconnect the connector by fully loosening the bolt.
PREPARATION
1. Turn the ignition switch to LOCK position.
2. Turn up the passenger side floor mat.
3. Remove the ECU protector.
4. Disconnect the connector from the ECU. After completely loosening the bolt, the two parts of the con-
nector can be separated.
NOTICE:
w Do not pully the wire harness when disconnecting the
connector.
w When disconnecting the connector, the ECU's backup
power source is cut off, so the malfunction codes, etc.
recorded in the ECU memory are cancelled.
w Never insert a tester probe or male terminal used for
inspection purposes into the female terminal of the
vehicle wire harness. Otherwise, the female terminal may
be widened, which can result in faulty connection.
5. Connect the Check Harness A between ECU and connector
of vehicle wire harness.
SST 09990±01000
HINT: The arrangement of the check connector terminals are
the same as those of the ECU.
See page TR±31
6. Disconnect the Check Harness A.
7. Reconnect the connector to the ECU.
(a) Match the male connector correctly with the femaleconnector, then press them together.
(b) Tighten the bolt Make sure the connector is completely connected, by
tightening the bolt until there is a clearance of less than
1 mm (0.04 in.) between bottom of the male connector
and end of the female connector.
8. Install the ECU protector and floor mat.
TR±30
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ENGINE TROUBLESHOOTING Terminals of ECU
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TR±88
TR±10
0
TR±12
2
TR±13
0
TR±13
6
TR±14
0
TR±11
4
TR±14
2 TR±108
TR±11
8
TR±12
4
TR±13
2
AC±84
ST±24
IG±24 IG±6
EM±30
AT±66
IN±32BE±381IG±7
IG±9
MATRIX CHART OF PROBLEM SYMPTOMS
When the malfunction code is not confirmed in the diagnostic code check and \
the problem still can not be con-
firmed in the basic inspection, then proceed to this step and perform troubles\
hooting according to the numbered
order given in the table below.
The circuits indicated by on the matrix chart can be inspected using th\
e TCCS checker.
±
ENGINE TROUBLESHOOTING Martrix Chart of Problem SymptomsTR±35
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INSPECTION PROCEDURE
1Check engine speed sensor, No. 1, No. 2 cam position sensor
C
OK
PFor 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
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ENGINE TROUBLESHOOTING Circuit Inspection
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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.
±
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±48.
Code No.Diagnostic Code Detecting ConditionTrouble Area
No NE signal to ECU for 0.1 sec. or more at
1,000 rpm or more.
wOpen or short in engine speed sensor
w circuit.
w Engine speed sensor
w ECU
13No 12 pulses of NE to ECU during the interval
between G1 and G2 pulses.
wOpen or short in engine speed sensor
w circuit.
w Mechanical system malfunction (skipping
teeth of timing belt, belt stretched)
w Engine speed sensor
w ECU
Deviation in G (G1, G2) and NE signal contin-
ues for 1 sec. during idling (throttle fully
closed) after engine warmed up.wMechanical system malfunction (skipping
teeth of timing belt, belt stretched)
w No. 1, No. 2 cam position sensor
w ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Inspect sensor installation. Check if any teeth of NE
signal plate are broken
Check valve timing (Check for loose and jumping teeth
of timing belt (See page EM±51)). Tighten the sensor.
Replace signal plate.
Adjust valve timing
(Repair or replace timing belt).
HINT: Perform troubleshooting of diag. code 12 first. If no trouble is found, trouble\
shoot the following mechanical systems.
Check for momentary interruption
(See page TR±23).
TR±52±
ENGINE TROUBLESHOOTING Circuit Inspection
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
Refer to inspection procedure in details.
HINT: If diag. code 14 is displayed, check No. 1 igniter circuit. If diag. code 15 is displayed, check No. 2 igniter circuit.
Check for spark.
Check for open and short in IGF signal circuit
between igniter and ECU.
Check voltage of terminal IGF.
Check and replace ECU.
Check voltage of terminal IGT.
Check voltage of igniter power source.
Check for open and short in primary coil circuit.
Check ignition coil.
Replace igniter.
Check and repair igniter power source circuit.
Check voltage of terminal IGT
(Disconnect igniter connector).
Check and repair igniter power source circuit. Repair or replace harness or
connector.
Replace igniter.
Repair or replace harness or
connector
Replace ignition relay.
Replace ignition relay.
Check for open and short in IGT signal circuit
between igniter and ECU.
Check and replace ECU. Repair or replace harness or
connectorReplace igniter.
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ENGINE TROUBLESHOOTING Circuit InspectionTR±55
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INSPECTION PROCEDURE
HINT: If diag. code 14 is displayed, check No. 1 igniter circuit. If diag. code 15 is displayed, check No. 2 igniter circuit.
1Check for Spark.
C
OK
Hint
Disconnect the high±tension cord from the distributor,
hold its end about 12.5 mm (1/2º) from the ground, see
if spark occurs while the engine is being cranked.
Spark should be generated.
To prevent excessive fuel injected from the injectors dur-
ing the check. Don't crank the engine for more than 1±2
seconds at a time.
Go to step [4].
2Check for open and short in harness and connector in the IGF and IGT signal c\
ircuit between
engine & ECT ECU and igniter (See page IN±27)
Repair or replace harness or connector.
#Disconnect igniter sonnector and check voltage between terminals IGF1, 2 of engine & ECT
ECU connector and body ground.
C
OK
P(2) Disconnect igniter connector.
(2) Connect the Check Harness A.
(See page TR±30).
(2) Turn ignition switch on.
Measure Voltage between terminals IGF1, 2 or engine
& ECT ECU connector and body ground.
Voltage: 4 ± 6 V
Replace igniter.*1
Check and replace engine & ECT ECU.
*1: When dia. code 14 is displayed, replace the igniter with 5 wire harness. (extra wire is for tachometer). When diag.
code 15 is displayed, replace the igniter with 4 wire har-
ness.
TR±56±
ENGINE TROUBLESHOOTING Circuit Inspection
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