ignition LEXUS SC300 1991 Service Repair Manual

Diagnosis Inspection (Test Mode)
Compared to the normal mode, the test mode has high sensing
ability to detect malfunctions.
It can also detect malfunctions in the starter signal circuit, the IDL
contact signal of the throttle position sensor, air conditioner signal
and neutral start switch signal.
Furthermore, the same diagnostic items which are detected in the
normal mode can also be detected in the test mode.
DIAGNOSTIC CODE CHECK
1. Initial conditions.(a) Battery voltage 11 V or more.
(b) Throttle valve fully closed (throttle position sensor IDLpoints closed).
(c) Transmission in neutral position.
(d) Air conditioner switched off.
2. Turn ignition switch off.
3. Using SST, connect terminals TE2 and E1 of TDCL. SST 09843±18020
4. Turn ignition switch on. HINT:
wTo confirm that the test mode is operating, check that the
ºCHECKº engine warning light flashes when the ignition
switch is turned to ON.
w If the ºCHECKº engine warning light does not flash,
proceed to tro ubleshooting of the TE2 terminal circuit on
page TR±146 .
5. Start the engine.
6. Simulate the conditions of the malfunction described by the customer.
7. After the road test, using SST, connect terminals TE1 and E1
of TDCL or check connector.
SST 09843±18020
8. Read the diagnostic code on ºCHECKº engine warning light on the combination meter (See page TR±11).
9. After completing the check, disconnect terminals TE1, TE2 and E1, and turn off the display.
HINT:
wThe test mode will not start if terminals TE2 and E1 are
connected after the ignition switch is turned on.
w When the engine is not cranked, diag. codes º43º
(Starter signal) output, but this is not abnormal.
w When the automatic transmission shift lever is in the ºDº,
º2º, ºLº or ºRº shift position, or when the air conditioner
is on or when the accelerator pedal is depressed, code
º51º (Switch condition signal) is output, but this is not
abnormal.
TR±12
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ENGINE TROUBLESHOOTING Diagnosis System
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DIAGNOSTIC CODE CLEARANCE
1. After repair of the trouble areas, the diagnostic code retainedin the ECU memory must be cleared out by removing the EFI
fuse (30A) from R/B No. 2 for 10 seconds or more, with the
ignition switch OFF.
HINT:
wCancellation can also be done by removing the battery
negative (±) terminal, but in this case, other memory
systems (clock, etc.) will also be cancelled out.
w If it is necessary to work on engine components
requiring removal of the battery terminal, a check must
first be made to see if a diagnostic code has been
recorded.
2. After cancellation, road test the vehicle to check that a normal
code is now read on the ºCHECKº engine warning light.
If the same diagnostic code appears, it indicates that the
trouble area has not been repaired thoroughly.
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ENGINE TROUBLESHOOTING Diagnosis SystemTR±13
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ºCHECKº Engine
Tro ble Area
CHECK Engine
Warning Light *
Memory*See PageTrouble AreaNormal
ModeTest
ModeMemory* See Page
w Open or short in water temp. sensor circuit.
w Water temp. sensor
w ECU
ONONTR±68
w Open or short in intake air tempsensor circuitOFFw Open or short in intake air temp. sensor circuit.
w Intake air tempsensor
OFF
ONTR 72w Intake air temp. sensor
ECUON*3
ONTR±72
w ECUON*3
w Open or short in main oxygen sensor circuit.w Oen or short in main oxygen sensor circuit.
w Main oxygen sensor
Main oxygen sensor
w Ignition systemgy
w Water temp. sensor
w Open or short in injector circuit.w Oen or short in injector circuit.
w Fuel line pressure
(injector blockage)w Fuel line ressure (injector blockage)
w Air flow meter (air intake)ONONTR±74 Air flow meter (air intake)
w Engine ground bolt loose

gg
w Foreign object caught in valve
w Fuel line pressure (injector leak, blockage)w Fuel line ressure (injector leak, blockage)
w Mechanical system malfunction Mechanical system malfunction
w(skipping teeth of timing belt)(g g)
w Ignition system
w Open or short in heater circuit of sub±oxygen sen-
sor.
w Sub±oxygen sensor heaterONN.A.w Sub±oxygen sensor heater.
w ECU
TR±82
w Open or short in sub±oxygen sensor circuit.
TR 82
w Oen or short in sub oxygen sensor circuit.
w Sub±oxygen sensor
ONON Sub oxygen sensor
w ECU
w Same as (1) of Code No. 21ONN.A.
TR 62w Same as (2) of Code No. 21ONONTR±62
w Same as (1) of Code No. 27ONN.A.
TR 82w Same as (2) of Code No. 27ONONTR±82
*1, 2, 3: See page TR±20.
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ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±17
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Trouble Area
ºCHECKº
Engine Warning
Light *

Memory* See PageTrouble Area
Normal
ModeTest
Mode
MemorySee Page
w Open or short in air flow meter circuit.
w Air flow meter
w ECU
ONN.A.TR±88
wECUONONTR±92
wOpen or short in throttle position sensor circuit.
wThrottle position sensorONONTR±94Throttle osition sensor
w ECU
wNo. 1 speed sensor
w Combination meter
w Open or short in No. 1 speed sensor circuit.
w ECU
ONONTR±98
wOpen or short in starter signal circuit.
w Open or short in ignition switch or main relay circuit.
w ECU
N.A.OFFXTR±100
wOpen or short in sub±throttle position sensor circuit.
wSub±throttle position sensorOFFONTR±94Sub throttle osition sensor
wECU
wOpen or short in No. 1 knock sensor circuit.wOen or short in No. 1 knock sensor circuit.
w No. 1 knock sensor (looseness)
ONN.A.No. 1 knock sensor (looseness)
wECU

w ECUONN.A.XTR±102
w Open or short in No. 2 knock sensor circuit.w Oen or short in No. 2 knock sensor circuit.
w No. 2 knock sensor (looseness)
ONN.A. No. 2 knock sensor (looseness)
w ECU

*1, 2: See page TR±20.
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ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±19
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FAIL±SAFE CHART
If any of the following codes is recorded, the ECU enters fail±
safe mode.
Code No.Fail±Safe OperationFail±Safe Deactivation Conditions
14Fuel cut1 IGF1 detected in consecutive 8 ignitions.
15Fuel cut1 IGF2 detected in consecutive 8 ignitions.
16Torque control prohibited.Returned to normal condition.
22THW is fixed at 805C (176 5F).Returned to normal condition.
24THA is fixed at 20 5C (68 5F).Returned to normal condition.
31
Ignition timing controlled between 10 5 ~ 30 5
BTDC,
Injection time controlled between 3 msec. ~ 30 m
sec., in relation to:
w Engine rpm
w Throttle angle
w ISC step value
KS input 15 times/sec. or more.
35Atmospheric pressure is fixed at 760 mmHg.Returned to normal condition.
The following 1 or 2 must be repeated at least 2
times consecutively.
41VTA1 is fixed at 051 When IDL is ON41VTA1 is fixed at 051 When IDL is ON
0.25 V
VTA1
0.95 V
2 When IDL is OFF2 When IDL is OFF
0.25 V
VTA1
4.9 V
The following 1 or 2 must be repeated at least 2
times consecutively.
47Value of VTA1 is used1 When IDL2 is ON47Value of VTA1 is used.1 When IDL2 is ON
0.25 V
VTA2
0.95 V
2 When IDL2 is OFF2 When IDL2 is OFF
0.25 V
VTA2
4.9 V
52Max. timeing retardation.IG switch OFF.
53Max. timeing retardation.Returned to normal condition.
55Max. timeing retardation.IG switch OFF.
Back±Up Function
If there is trouble with the program in the ECU and the ignition signals\
(IGT) are not output, the ECU controls
fuel injection and ignition timing at predetermined levels as a back±up f\
unction to make it possible to continue
to operate the vehicle.
Furthermore, the injection duration is calculated from the satrting sign\
al (STA) and the throttle position signal
(IDL). Also, the ignition timing is fixed at the initial ignition timing, 5 5 BTDC, without relation to the engine speed.
HINT: If the engine is controlled by the back±up function, the CHECK ENGIN\
E light lights up to warn the driver
of the malfunction but the diagnostic code is not output. TR±22
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ENGINE TROUBLESHOOTING Fail±Safe Chart
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CHECK FOR MOMENTARY
INTERRUPTION
As described in the preceding paragraph, abnormality detection
ability in the test mode is increased compared to that in the normal
mode, so that when momentary interruptions or momentary shorts
occur in the ECU signal circuits (G1, G2, NE, THW, THA, VTA1,
VTA2) shown in the table below, the appropriate diagnostic code
is output.
Accordingly, when the diagnostic codes shown in the table below
(13, 22, 24, 41, 47) are output during the diagnostic code check,
and inspection of the appropriate circuits reveals no abnormality,
perform the check for momentary interruption as described below.
By performing the check for momentary interruption, the place
where momentary interruptions or momentary shorts are occur-
ring due to poor contacts can be isolated.
CLEAR DIAGNOSTIC CODES
See page TR±13.
SET TEST MODE
1. With the ignition switch off, using SST, connect the terminals
TE2 and E1 of the TDCL.
SST 09843±18020
2. Start the engine and check to see the ºCHECKº engine warning light to go off.
PERFORM A SIMULATION TEST
Using the symptom simulation (See page IN±20), apply vibration
to and pull lightly on the wire harness, connector or terminals in the
circuit indicated by the malfunction code.
In this test, if the ºCHECKº engine warning light lights up, it in\
di-
cates that the place where the wire harness, connector or termi-
nals being pulled or vibrated has faulty contact. Check that point
for loose connections, dirt on the terminals, poor fit or other prob-
lems and repair as necessary.
HINT: After cancelling out the diagnostic code in memory and set
the test mode, if the ºCHECKº engine warning light does not go off
after the engine is started, check thoroughly for faulty contact,
etc., then try the check again. If the ºCHECKº engine warning light
still does not go off, check and replace ECU.
±
ENGINE TROUBLESHOOTING Check for Momentary InterruptionTR±23
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OKNG
OKNG
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 .
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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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FAIL±SAFE CHART
If any of the following codes is recorded, the ECU enters fail±safe mod\
e.
Code No.Fail±Safe OperationFail±Safe Deactivation Conditions
14Fuel cut1 IGF detected in consecutive 3 ignitions.
16Torque control prohibited.Returned to normal condition.
22THW is fixed at 805C (176 5F).Returned to normal condition.
24THA is fixed at 20 5C (68 5F).Returned to normal condition.
31 Ignition timing fixed at 10 5 BTDC.
 Injection time fixed
Starting 9 m sec.KS input 15 times/sec. or more.
IDL ON 3.6 m sec.
IDL OFF 6.7 m sec.
35Atmospheric pressure is fixed at 101.3 kPa
(760 mmHg 29 92 in Hg)
Returned to normal condition.
(760 mmHg, 29.92 in.Hg).
41VTA1 is fixed at 05.The following must each be repeated at least 241VTA1 is fixed at 0 5.The following must each be re eated at least 2
time consecutively.time consecutively.
(w/o TRAC)(w/o TRAC)
 0.1 V ? VTA ? 0.95 V 0.1 V ? VTA ? 0.95 V
 IDL : ON
( / TRAC)(w/ TRAC)
025V?VTA?095V  0.25 V ? VTA ? 0.95 V
 IDL:ON  IDL : ON
52Max. timing retardation.IG switch OFF.
53Max. timing retardation.Returned to normal condition.
55Max. timing retardation.IG switch OFF.
Back±Up Function
If there is trouble with the program in the ECU and the ignition signals\
(IGT) are not output, the ECU controls
fuel injection and ignition timing at predetermined levels as a back±up f\
unction to make it possible to continue
to operate the vehicle.
Furthermore, the injection duration is calculated from the starting sign\
al (STA) and the throttle position signal
(IDL). Also, the ignition timing is fixed at the initial ignition timing, 10 5 BTDC, without relation to the engine speed.
HINT: If the engine is controlled by the back±up function, the ºCHECKº\
engine warning light lights up to warn
the driver of the malfunction but the diagnostic code is not output. TR±26
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ENGINE TROUBLESHOOTING Fail±Safe Chart
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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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