1991 LEXUS SC400 ECO mode

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.
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ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±21
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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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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 or TDCL with IG
switch OFF).
Start the engine and warm up with all ACC switch OFF.
After the engine is warmed up, let it idle for 3 min.
After performing the idling in , perform gradual acceleration with in th\
e range 1,300
1,700 rpm (centered around 1,500 rpm) with the A/C switch ON and D range fo\
r A/T
(5th for M/T).
(Take care that the engine speed does not fall below 1,200 rpm when shifting.\
Gradu-
ally depress the accelerator pedal and kept it. Steady so that engine br\
aking does not
occur).
Maintain the vehicle speed at 40±50 mph (64±80 km/h).
Keep the vehicle running for 1±2 min. after starting acceleration.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light\
up after approx. 60 sec. from the start of acceleration.
NOTICE: If the conditions in this test are not strictly followed, detection of t\
he malfunction will not be possible.
Malfunction: Main Oxygen Sensor Deterioration
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ENGINE TROUBLESHOOTING Circuit InspectionTR±61
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CIRCUIT DESCRIPTION (Cont'd)
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 confirming that diag.code is no longer detected.
DIAGNOSIS CODE DETECTION DRIVING PATTERN
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 ON), perform
gradual acceleration with in the range 1,300 ± 1,700 rpm (centered
around 1,500 rpm).
(Take care that the engine speed does not fall below 1,200 rpm when
shifting. Gradually depress the accelerator pedal and kept it. Steady so
that engine braking does not occur.)
Maintain the vehicle speed at 40 ± 50 mph (64 ± 80 km/h).
Keep the vehicle running for 1 ± 2 min. after starting acceleration.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light\
up af-
ter approx. 60 sec. from the start of acceleration.
NOTICE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
TR±63
±
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 or TDCL with IG
switch OFF).
Start engine and warm up with all ACC switch OFF.
After engine is warmed up, let it idle for 5 min.
(After the engine is started, do not depress the accelerator pedal.)
If the malfunction is not detected during idling, perform racing without any load at
approx. 2,000 rpm for 60 sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light\
up during the 5 min. idling period or within 60 sec. of starting racing.
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 Injector circuit, Injector Leak or Blockag\
e
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ENGINE TROUBLESHOOTING Circuit InspectionTR±71
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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 c\
onfirming that diag. code is no longer detected.
Malfunction: Open or Short in Main 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.
Perform quick racing to 4,000 rpm three times by accelerator pedal.
After performing the racing in (4), perform racing at 2,000 rpm for 90\
sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light up after 90 sec. from the start of racing.
NOTICE: If the conditions in this test are not strictly followed, detection of t\
he malfunction will not be possible.
TR±75±
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. codeis no longer detected.
Malfunction: Open or Short in Injector circuit, Injector Leak or Blockage, Loose E/G Earth Bolt.

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 5 min.
(After the engine is started, do not depress the accelerator pedal.)
\bIf the malfunction is not detected during idling, perform racing without a\
ny load at approx.
2,000 rpm for 30 sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light up during the 5 min. idling
period or within 30 sec. of starting racing.
NOTICE: If the conditions in this test are not strictly followed, detection of the\
malfunction will not be possible.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±76
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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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ENGINE TROUBLESHOOTING Circuit InspectionTR±77
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