LEXUS SC400 1991 Service Repair Manual

How to Proceed with Troubleshooting Using Volt/Ohm Meter
and TCCS Checker
For the explanation of steps [1] ~ [6], [8] and [10] ~ [16], see the explan\
ation of steps with the same title on page
TR±2.
[7] [9] CIRCUIT INSPECTION BY CHECKER If the Normal code is displayed in the diagnostic code check, connect the \
checker to the vehicle and check
all the circuits which can be inspected using the checker.
If a malfunctioning circuit is then detected, proceed to ºCircuit Ins\
pection by Volt/Ohm Meterº and check
the applicable circuit using a volt/ohm meter. Determine if the malfunction is in the sensor, actuator, wire
harness, connector or the ECU. If the malfunctioning circuit cannot be detected u\
sing the checker, proceed
to ºBasic Inspectionº and perform troubleshooting.
If a malfunction code is displayed in the diagnostic code check, use the c\
hecker to inspect the circuit indi-
cated by the diagnostic code chart for the displayed code.
For instructions on how to connect the checker to the vehicle and how to us\
e the checker, please refer to
the Instruction Manual for TCCS checker.
TR±6
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ENGINE TROUBLESHOOTING How to Proceed with Troubleshooting
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P. TR±8
P. TR±11 , TR±13
P. TR±12
P. IN±20
P. TR±12
P. TR±14
P. TR±24
P. TR±35
P. TR±48
P. TR±23
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ENGINE TROUBLESHOOTING How to Proceed with TroubleshootingTR±7
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CUSTOMER PROBLEM ANALYSIS CHECK SHEET
TR±8±
ENGINE TROUBLESHOOTING Customer Problem Analysis
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±MEMO±
ENGINE TROUBLESHOOTINGTR±9
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DIAGNOSIS SYSTEM
DESCRIPTION
The ECU contains a built±in self±diagnosis system by which
troubles with the engine signal network are detected and a
ºCHECKº engine warning light on the instrument panel lights up.
By analyzing various signals as shown in the later table (See page
TR±14) the Electronic Control Unit (ECU) detects system malfunc-
tions relating to the sensors or actuators.
In the normal mode, the self±diagnosis system monitors 22 (USA
specification vehicles with TRAC control) or 21 (USA (except for
California) and Canadian specification vehicles with TRAC con-
trol) items, indicated by code No. as shown in TR±14. A ºCHECKº
engine warning light informs the driver that a malfunction has been
detected. The light goes off automatically when the malfunction
has been repaired. But the diagnostic code(s) remains stored in
the ECU memory (except for code Nos. 16 and 53). The ECU
stores the code(s) until it is cleared by removing the EFI fuse with
the ignition switch off.
The diagnostic code can be read by the number of blinks of the
ºCHECKº engine warning light when TE1 and E1 terminals on the
TDCL or check connector are connected. When 2 or more codes
are indicated, the lowest number (code) will appear first.
In the test mode, 15 (USA specification vehicles with TRAC con-
trol) or 14 (USA (except for California) and Canadian specification
vehicles with TRAC control) items, indicated by code No. as
shown in TR±14 are monitored. If a malfunction is detected in any
one of the systems indicated by code Nos. 13, 21, 22, 24, 25, 26,
27, 28, 29, 35, 41, 42, 47, 71 and 78 (USA specification vehicles)
or 13, 21, 22, 24, 25, 26, 27, 28, 29, 35, 41, 42, 47 and 78 (USA
(except for California) and Canadian specification vehicles) the
ECU lights the ºCHECKº engine warning light to warn the techni-
cian that malfunction has been detected. In this case, TE2 and E1
terminals on the TDCL should be connected as shown later. (See
page TR±12 ).
In the test mode, even if the malfunction is corrected, the malfunc-
tion code is stored in the ECU memory even when the ignition
switch is off (except code Nos. 43 and 51). This also applies in the
normal mode. The diagnostic mode (normal or test) and the output
of the ºCHECKº engine warning light can be selected by connect-
ing the TE1, TE2 and E1 terminals on the check connector or
TDCL, as shown later.
A test mode function has been added to the functions of the self±
diagnosis system of the normal mode for the purpose of detecting
malfunctions such as poor contact, which are difficult to detect in
the normal mode. This function fills up the selfdiagnosis system.
The test mode can be implemented by the technician following the
appropriate procedures of check terminal connection and opera-
tion described later. (See page TR±12)
TR±10
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ENGINE TROUBLESHOOTING Diagnosis System
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Diagnosis Inspection (Normal Mode)
ºCHECKº ENGINE WARNING LIGHT
CHECK
1. The ºCHECKº engine warning light will come on when theignition switch is turned ON and the engine is not running.
HINT: If the ºCHECKº engine warning light does not light up,
proceed to troubleshooting of the combination meter (See
page
BE±146).
2. When the engine is started, the ºCHECKº engine warning light should go off.
If the light remains on, the diagnosis system has detected a
malfunction or abnormality in the system.
DIAGNOSTIC CODE CHECK
1. Turn ignition switch on.
2. Using SST, connect terminals between TE1 and E1 of TDCLor check connector.
SST 09843±18020
3. Read the diagnostic code from ºCHECKº engine warning light.
HINT: If a diagnostic code is not output, check the TE1 termi-
nal circuit (See page TR±146).
As an example, the blinking patterns for codes;normal, 12
and 31 are as shown on the illustration.
4. Check the details of the malfunction using the diagnostic
code table on page TR±14.
5. After completing the check, disconnect terminals TE1 and E1, and turn off the display.
HINT: In the event of 2 or more malfunction codes, indication
will begin from the smaller numbered code and continue in
order to the larger.
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ENGINE TROUBLESHOOTING Diagnosis SystemTR±11
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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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DIAGNOSTIC CODE CHART
HINT: Parameters listed in the chart may not be exactly same as your reading \
due to type of the instruments
or other factors.
*4: See page TR±21.
TR±14
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ENGINE TROUBLESHOOTING Diagnostic Code Chart
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If a malfunction code is displayed during the diagnostic code check in tes\
t mode, check the circuit for that code
listed in the table below (Proceed to the page given for that circuit).
Tro ble Area
ºCHECKº EngineWarning Light *
Memory*See Page
Trouble AreaNormal
ModeTest
Mode
±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
w Open or short in engine speed sensor, No. 1, No. 2
cam position sensor circuit.
w Engine speed sensor
w No. 1, No. 2 cam position sensor
w Starter
w ECU
ONN.A.TR±48
w Open or short in engine speed sensor circuit.w Oen or short in engine s eed sensor circuit.
w Engine speed sensor
ONN.A. Engine s eed sensor
w ECU
ONN.A.
w Open or short in engine speed sensor circuit.g
w Mechanical system malfunction (skipping teeth of
ti itiming
wbelt belt stretched)N.A.ONTR 52wbelt, belt stretched)
wEngine speed sensor
TR±52
w Engine s eed sensor
w ECU
w Mechanical system malfunction (skipping teeth ofw Mechanical system malfunction (ski ing teeth of
wtiming belt, belt stretched)ONNAwtiming belt, belt stretched)
w No. 1, No. 2 cam position sensorONN.A. No. 1, No. 2 cam osition sensor
w ECU
w Open or short in IGF1 circuit from igniter No.
1±ECU.
w Igniter No. 1
w ECU
ONN.A.TR±54
w Open or short in IGF2 circuit from igniter No.
2±ECU.
w Igniter No. 2
w ECU
ONN.A.TR±54
w ECUONN.A.XTR±61
w Open or short in heater circuit of main oxygen sen-
sor.
w Main oxygen sensor heaterONN.A.w Main oxygen sensor heater
w ECU
TR±62
w Main oxygen sensor circuit
w
Main oxygen sensorONONw Main oxygen sensor
*1, 2: See page TR±20.
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ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±15
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