stop start LEXUS SC300 1991 Service Service Manual

Diag. Code 14, 15Ignition Signal Circuit
CIRCUIT DESCRIPTION
The ECU determines the ignition timing, turns on Tr1 at a predetermined angle (5CA) before the desired
ignition timing and outputs an ignition signal (IGT) º1º to the \
igniter.
Since the width of the IGT signal is constant, the dwell angle control circuit in the ignit\
er determines the
time the control circuit starts primary current flow to the ignition coil bas\
ed on the engine rpm and ignition
timing one revolution ago, that is, the time the Tr2 turns on.
When it reaches the ignition timing, the ECU turns Tr1 off and outputs the IGT signal ºOº.
This turns Tr2 off, interrupting the primary current flow and generating a high voltage i\
n the secondary coil
which causes the spark plug to spark. Also, by the counter electromotive force\
generated when the primary
current is interrupted, the igniter sends an ignition confirmation signal (IGF\
) to the ECU.
The ECU stops fuel injection as a fail safe function when the IGF signal\
is not input to the ECU.
Code No.Diagnostic Code Detecting ConditionTrouble Area
14No IGF1 signal to ECU for 8±11 consecutive
IGT1 signal.
w Open or short in IGF1 and IGT1 circuit from
No. 1 igniter ± ECU.
w No. 1 igniter
w ECU
15No IGF2 signal to ECU for 8±11 consecutive
IGT2 signal.
wOpen or short in IGF2 and IGT2 circuit from
No. 2 igniter ± ECU.
w No. 2 igniter
w ECU
HINT: No. 1 igniter is for left bank and No. 2 igniter is for right bank.
WIRING DIAGRAM
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CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed co\
nfirming that diag. code isno longer detected.

Disconnect the EFI fuse (15 A) for 10 sec. or more, with IG switch OFF\
.
Initiate test mode (Connect terminal TE2 and E1 of check connector with\
IG switch
OFF).
Start the engine and warm up with all ACC switch OFF.
After the engine is warmed up, let it drive at 50 55 mph (80 88 km/h) for\
10 min. or
more.
After driving, stop at a safe place and perform idling for 2 min. or les\
s.
After performing the idling in , perform acceleration to 60 mph (96 km/h) with the
throttle valve fully open.
HINT: If a malfunction exists, the ºCHECKº engine warning light will lig\
ht up during step
.
NOTICE: If the conditions in this test are not strictly followed, detection of t\
he malfunction will not be possible.
Malfunction: Open or Short in Sub±Oxygen Sensor
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CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed co\
nfirming that diag. codeis no longer detected.
Malfunction: Open or Short in Sub±Oxygen Sensor

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 3 min.
With the A/C ON and the transmission in D range (O/D OFF), drive at 40 ±\
60 mph (64±96
km/h) for 6 min.
After the driving in , stop the vehicle.
Once the vehicle is stopped, within the next minute apply acceleration w\
ith the throttle
fully open for 4 sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light\
up after full acceleration for 4 sec.
NOTICE: If the conditions in this test are not strictly followed, detection of the\
malfunction will not be possible.
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Cold Start Injector Circuit
CIRCUIT DESCRIPTION
The cold start injector is used to maintain the engine startability when it\
is cold. The injection volume, i,e, the
length of time the injector is energized, is controlled by the ECU and t\
he cold start injector time switch.
During a cold start, when the starter turns the contacts in the cold start inj\
ector time switch close. Thus current
flows to the cold start injector coil, injecting fuel. At the same time, a bi\
metal in the heat coil is energized and
heats up. This soon causes the contacts to open, cutting off the current flow to the injector coil and stopping
fuel injection.
The injection duration of the cold start injector is determined by the cool\
ant temperature and the length of time
current flows to the heat coil. When the engine is warm, the contacts are opened by the bimetal and the cold
start injector does not operate.
When the engine is hard to start and the starter is operated continuously, heat coil (2) heats up the bimetal keep-
ing the contacts open to prevent spark plugs from becoming fouled, which is\
caused by the cold start injector
operation when the open contacts close again.
When the engine is started at a coolant temperature of 225C (72 5F) or lower, the cold start injector operation
time is controlled by the cold start injector time switch.
When the coolant temperature is in the normal temperature range 22 5C (72 5F) or higher, the contacts of the cold
start injector time switch are open and the time switch is off, instead, the ECU controls the operating time of the
cold start injector.
In this way, the CO and HC levels can be reduced while the engine is being started \
and the engine startability
is maintained. Control by the ECU ends when the coolant temperature reac\
hes 60 5C (140 5F).
TR±136±
ENGINE TROUBLESHOOTING Circuit Inspection
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YESNO
NOYES
YES
NO
OKNG
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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Diag. Code 14, 15Ignition Signal Circuit
CIRCUIT DESCRIPTION
The ECU determines the ignition timing, turns on Tr1 at a predetermined angle (5CA) before the desired
ignition timing and outputs an ignition signal (IGT) º1º to the \
igniter.
Since the width of the IGT signal is constant, the dwell angle control circuit in the ignit\
er determines the
time the control circuit starts primary current flow to the ignition coil bas\
ed on the engine rpm and ignition
timing one revolution ago, that is, the time the Tr2 turns on.
When it reaches the ignition timing, the ECU turns Tr1 off and outputs the IGT signal ºOº.
This turns Tr2 off, interrupting the primary current flow and generating a high voltage i\
n the secondary coil
which causes the spark plug to spark. Also, by the counter electromotive force\
generated when the primary
current is interrupted, the igniter sends an ignition confirmation signal (IGF\
) to the ECU.
The ECU stops fuel injection as a fail safe function when the IGF signal\
is not input to the ECU.
Code No.Diagnostic Code Detecting ConditionTrouble Area
14No IGF1 signal to ECU for 8±11 consecutive
IGT1 signal.
w Open or short in IGF1 and IGT1 circuit from
No. 1 igniter ± ECU.
w No. 1 igniter
w ECU
15No IGF2 signal to ECU for 8±11 consecutive
IGT2 signal.
wOpen or short in IGF2 and IGT2 circuit from
No. 2 igniter ± ECU.
w No. 2 igniter
w ECU
HINT: No. 1 igniter is for left bank and No. 2 igniter is for right bank.
WIRING DIAGRAM
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ENGINE TROUBLESHOOTING Circuit Inspection
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CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed co\
nfirming that diag. code isno longer detected.

Disconnect the EFI fuse (15 A) for 10 sec. or more, with IG switch OFF\
.
Initiate test mode (Connect terminal TE2 and E1 of check connector with\
IG switch
OFF).
Start the engine and warm up with all ACC switch OFF.
After the engine is warmed up, let it drive at 50 55 mph (80 88 km/h) for\
10 min. or
more.
After driving, stop at a safe place and perform idling for 2 min. or les\
s.
After performing the idling in , perform acceleration to 60 mph (96 km/h) with the
throttle valve fully open.
HINT: If a malfunction exists, the ºCHECKº engine warning light will lig\
ht up during step
.
NOTICE: If the conditions in this test are not strictly followed, detection of t\
he malfunction will not be possible.
Malfunction: Open or Short in Sub±Oxygen Sensor
±
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CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed co\
nfirming that diag. codeis no longer detected.
Malfunction: Open or Short in Sub±Oxygen Sensor

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 3 min.
With the A/C ON and the transmission in D range (O/D OFF), drive at 40 ±\
60 mph (64±96
km/h) for 6 min.
After the driving in , stop the vehicle.
Once the vehicle is stopped, within the next minute apply acceleration w\
ith the throttle
fully open for 4 sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light\
up after full acceleration for 4 sec.
NOTICE: If the conditions in this test are not strictly followed, detection of the\
malfunction will not be possible.
±
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139
(FOR ABS)
THIS SYSTEM CONTROLS THE RESPECTIVE BRAKE FLUID PRESSURES ACTING ON THE DISC\
BRAKE CYLINDERS OF THE RIGHT
FRONT WHEEL, LEFT FRONT WHEEL AND REAR WHEELS WHEN THE BRAKES ARE APPLIED IN \
A PANIC STOP SO THAT THE
WHEELS DO NOT LOCK. THIS RESULTS IN IMPROVED DIRECTIONALLY STABILITY AND STEERABILITY DURING PANIC BRAKING.
1. INPUT SIGNALS
(1) SPEED SENSOR SIGNALTHE SPEED OF THE WHEELS IS DETECTED AND INPUT TO TERMINALS FL+, FR+, RL+ AND RR+ OF THE ABS AND TRACTION
ECU.
(2) STOP LIGHT SW SIGNAL A SIGNAL IS INPUT TO TERMINAL STP OF THE ABS AND TRACTION ECU WHEN THE BRAKE PEDAL IS OPERATED.
(3) PARKING BRAKE SW SIGNAL A SIGNAL IS INPUT TO TERMINAL PKB OF THE ABS AND TRACTION ECU WHEN THE PARKING BRAKE IS OPERATED.
2. SYSTEM OPERATION
DURING SUDDEN BRAKING, THE ABS AND TRACTION ECU WHICH HAS SIGNALS INPUT FROM E\
ACH SENSOR CONTROLS THE
CURRENT FLOWING TO THE SOLENOID INSIDE THE ACTUATOR AND LETS THE HYDRAULIC PRESSURE ACTING ON EACH WHEEL
CYLINDER ESCAPE TO THE RESERVOIR. THE PUMP INSIDE THE ACTUATOR IS ALSO OPERATING AT THIS TIME AND IT RETURNS
THE BRAKE FLUID FROM THE RESERVOIR TO THE MASTER CYLINDER, THUS PREVENTING LOCKING OF THE VEHICLE WHEELS.
IF THE ECU JUDGES THAT THE HYDRAULIC PRESSURE ACTING ON THE WHEEL CYLINDER IS INSUFFICIENT, THE CURRENT
ACTING ON SOLENOID IS CONTROLLED AND THE HYDRAULIC PRESSURE IS INCREASED, HOLD\
ING OF THE HYDRAULIC
PRESSURE IS ALSO CONTROLLED BY THE COMPUTER, BY THE SAME METHOD AS ABOVE. BY REP\
EATED PRESSURE REDUCTION,
HOLDING AND INCREASE ARE REPEATED TO MAINTAIN VEHICLE STABILITY AND TO IMPROVE STEERABILITY DURING SUDDEN
BRAKING.
(FOR TRACTION CONTROL)
THE TRACTION CONTROL SYSTEM IS A SYSTEM WHEREBY THE ªABS AND TRACTION ECUº AND ªTRACTION ECUº\
CONTROLS THE
ENGINE TORQUE AND THE HYDRAULIC PRESSURE OF THE WHEEL CYLINDER OF THE DRIVING WHEELS IN ORDER TO CONTROL
SPINNING OF THE DRIVING WHEELS WHEN STARTING OFF AND ACCELERATING, AND PROVIDE THE MOST APPROPRIATE DRIVING
FORCE IN RESPONSE TO THE ROAD CONDITIONS FOR VEHICLE STABILITY.
TRACTION CONTROL OPERATION
VEHICLE SPEED SIGNALS FROM THE SPEED SENSOR INSTALLED ON EACH WHEEL ARE INPUT TO THE ABS AND TRACTION ECU.
WHEN THE ACCELERATOR PEDAL IS DEPRESSED WHILE DRIVING ON A SLIPPERY ROAD AND THE DRIVING WHEEL (REAR WHEEL)
SLIPS, IF THE ROTATION OF THE REAR WHEEL EXCEEDS THE ROTATION OF THE FRONT WHEELS FOR A SPECIFIED PERIOD, THE
ECU JUDGES THAT THE REAR WHEEL IS SLIPPING.
WHEN THIS OCCURS, CURRENT FLOWS FROM TRACTION ECU TO SUB THROTTLE ACTUATOR TO CLOSE THE SUB THROTTLE
VALVE. THE THROTTLE VALVE OPENING ANGLE SIGNAL IS OUTPUT FROM TERMINAL VTA OF SUB THROTTLE POSITION SENSOR
TO TERMINAL VTA2 OF ENGINE AND ECT ECU TO KEEP THE ENGINE RPM AT THE MOST SUITABLE LEVEL FOR THE DRIVING
CONDITIONS AND REDUCE SLIP OF THE DRIVING WHEEL. AT THE SAME TIME, OPERATION OF THE ABS AND TRACTION ECU
CAUSE THE TRACTION BRAKE ACTUATORS (ACC CUT, M/C CUT, RESERVOIR CUT SOLENOID) TO TURN ON TO SWITCH THE
HYDRAULIC CIRCUIT TO ªTRACTIONº MODE.
IN THIS CASE, SIGNALS ARE INPUT FROM TERMINAL SRR OF ABS AND TRACTION ECU TO TERMINAL (B)6 OF ABS ACTUATOR, AND
FROM TERMINAL SRL OF ABS AND TRACTION ECU TO TERMINAL (B)1 OF ABS ACTUATOR, CONTROLLING THE REAR WHEEL
SOLENOID IN THE ABS ACTUATOR AND INCREASING THE HYDRAULIC PRESSURE OF THE WHEEL CYLINDER IN ORDER \
TO
PREVENT SLIP.
TO MAINTAIN THE HYDRAULIC PRESSURE OF THE REAR WHEELS, THE REAR WHEEL SOLENOID I\
NSIDE THE ABS ACTUATOR IS
PUT IN ªHOLDº MODE AND KEEPS THE HYDRAULIC PRESSURE TO THE BRAKE CYLINDER CONSTANT.
WHEN THE BRAKE CYLINDER HYDRAULIC PRESSURE IS REDUCED, THE PRESSURE REDU\
CTION MODE REDUCES AND CONTROLS
THE HYDRAULIC PRESSURE.
SYSTEM OUTLINE
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227
4. OPERATION OF AIR MIX CONTROL SERVO MOTOR
WHEN THE TEMPERATURE SW IS TURNED TO THE ªCOOLº SIDE, THE CURRENT FLOWS FROM TERMINAL MC OF A/C CONTROL
ASSEMBLY " TERMINAL 4 OF AIR MIX CONTROL SERVO MOTOR " MOTOR " TERMINAL 5 " TERMINAL MH OF A/C CONTROL
ASSEMBLY " GROUND AND THE MOTOR ROTATES. THE DAMPER OPENING ANGLE AT THIS TIME IS INPUT FROM TERMINAL 1 OF
SERVO MOTOR TO TERMINAL TP OF A/C CONTROL ASSEMBLY, THIS IS USED TO DETERMINE THE DAMPER STOP POSITION AND
MAINTAIN THE SET TEMPERATURE.
WHEN THE TEMPERATURE CONTROL SW IS TURNED TO THE ªHOTº SIDE, THE CURRENT FLOWS FROM SERVO MOTOR "
TERMINAL MH OF A/C CONTROL ASSEMBLY " TERMINAL 5 OF AIR MIX CONTROL SERVO MOTOR " MOTOR " TERMINAL 1 "
TERMINAL MC OF A/C CONTROL ASSEMBLY, ROTATING THE MOTOR IN REVERSE AND SWITCHING THE DAMPER FROM ªCOOLº TO
ªHOTº SIDE.
5. AIR CONDITIONER OPERATION
THE A/C CONTROL ASSEMBLY RECEIVES VARIOUS SIGNALS, I.E., THE ENGINE RPM FROM THE IGNITER, OUTLET TEMPERATURE
SIGNAL FROM THE A/C THERMISTOR, COOLANT TEMPERATURE FROM THE WATER TEMP. SENSOR AND THE LOCK SIGNAL FROM
THE A/C COMPRESSOR, ETC.
WHEN THE ENGINE IS STARTED AND THE A/C SW (A/C CONTROL ASSEMBLY) IS ON, A SIGNAL IS INPUT TO THE ECU. (BUILT IN THE
A/C CONTROL ASSEMBLY).
AS A RESULT, THE GROUND CIRCUIT IN A/C CONTROL ASSEMBLY IS CLOSED AND CURRENT FLOWS FROM HEATER FUSE (10A) TO
TERMINAL 2 OF MAGNETIC CLUTCH RELAY " TERMINAL 3 " TERMINAL ACMG OF ENGINE AND ECT ECU " TERMINAL E OF A/C
CONTROL ASSEMBLY " GROUND , TURNING THE MAGNETIC CLUTCH RELAY ON, SO THAT THE MAGNETIC CLUTCH IS ON AND THE
A/C COMPRESSOR OPERATES.
AT THE SAME TIME, THE ENGINE AND ECT ECU DETECTS THE MAGNETIC CLUTCH IS O\
N AND THE A/C COMPRESSOR OPERATES.
OPEN DIRECTION TO AVOID LOWERING THE ENGINE RPM DURING A/C OPERATING.
WHEN ANY OF THE FOLLOWING SIGNALS ARE INPUT TO THE A/C CONTROL ASSEMBLY, THE CONTROL ASSEMBLY OPERATES TO
TURN OFF THE AIR CONDITIONING.
* ENGINE HIGH TEMP. SIGNAL IS HIGH.
* COOLANT HIGH TEMP. SIGNAL IS HIGH.
* A SIGNAL THAT THE TEMPERATURE AT THE AIR OUTLET IS LOW.
* A SIGNAL THAT THERE IS A LARGE DIFFERENCE BETWEEN ENGINE RPM AND COMPRESSOR RPM.
* A SIGNAL THAT THE REFRIGERANT PRESSURE IS ABNORMALLY HIGH OR LOW.
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