1991 LEXUS SC400 sensor

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
±
ENGINE TROUBLESHOOTING How to Proceed with Troubleshooting
WhereEverybodyKnowsYourName

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
±
ENGINE TROUBLESHOOTING Diagnosis System
WhereEverybodyKnowsYourName

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
±
ENGINE TROUBLESHOOTING Diagnosis System
WhereEverybodyKnowsYourName

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.
±
ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±15
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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.
±
ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±17
WhereEverybodyKnowsYourName

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.
±
ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±19
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Trouble Area
ºCHECKº
Engine Warning
Light*

Memory* See PageTrouble Area
Normal
ModeTest
Mode
MemorySee Page
w Open or short in EGR step motor circuit.ONNA Oen or short in EGR ste motor circuit.
w ECUONN.A.
w Open in EGR gas temp. sensor circuit.ONON
TR±108 Oen in EGR gas tem . sensor circuit.
w ECUONON
w Open or short in fuel pump ECU circuit.
w Fuel pump ECU
w Engine & ECT ECU power source circuit.
w Fuel pump
w Engine & ECT ECU
ONONTR±114
w A/C switch circuit
w Throttle position sensor IDL circuit
w Neutral start switch circuit.
w Accelerator pedal and cable
w ECU
N.A.OFFXTR±118
*4: This indicates items for which º2 trip detection logicº is used. With this logic, when a lo\
gic malfunction is
first detected, the malfunction is temporarily stored in the ECU memory. If the same case is detected again
during the second drive test, this second detection causes the ºCHECK\
º Engine Warning Light to light up.
The 2 trip repeats the same mode a 2nd time. (However, the IG switch must be turned OFF between the
1st trip and 2nd trip).
In the Test Mode, the ºCHECKº Engine Warning Light lights up the 1st trip a malfunction is detected.
±
ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±21
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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
WhereEverybodyKnowsYourName