1991 LEXUS SC400 Service Repair Manual

4WD glove box key fob key battery open bonnet radio antenna

Page 3681 of 4087

$LEXUS SC400 1991 Service Repair Manual NGOK OKNG OKNG INSPECTION PROCEDURE HINT: If diagnostic codes º22º (water temperature sensor circuit), º2\ 4º (intake air temperature sensor cir-cuit) and º41º (throttle position sensor circuit$

Page 3682 of 4087

LEXUS SC400 1991 Service Repair Manual
Diag. Code 22Water Temp. Sensor Circuit
CIRCUIT DESCRIPTION
The water temperature sensor senses the coolant tem-
perature. A thermistor built in the sensor changes the
resistance value according t

Page 3683 of 4087

$LEXUS SC400 1991 Service Repair Manual DIAGNOSTIC CHART DIAGNOSTIC CHART HINT: If diagnostic codes º22º (water temperature sensor circuit), º\ 24º (intake air temperature sensorcircuit) and º41º (throttle position sensor circuit)$

Page 3684 of 4087

$LEXUS SC400 1991 Service Repair Manual NGOK OKNG OKNG INSPECTION PROCEDURE HINT: If diagnostic codes º22º (water temperature sensor circuit), º\ 24º (intake air temperature sensor circuit)and º41º (throttle position sensor circuit)$

Page 3685 of 4087

LEXUS SC400 1991 Service Repair Manual
±MEMO±TR±71
ENGINE TROUBLESHOOTING
WhereEverybodyKnowsYourName

Page 3686 of 4087

LEXUS SC400 1991 Service Repair Manual
Diag Code 25 26

Air±Fuel Ratio Lean Malfunction
Diag. Code 25, 26
Air±Fuel Ratio Rich Malfunction
CIRCUIT DESCRIPTION
Refer to page TR±62 for the circuit description.
Code No.
Diagnostic Code Det

Diag Code 25 26

Air±Fuel Ratio Lean Malfunction
Diag. Code 25, 26
Air±Fuel Ratio Rich Malfunction
CIRCUIT DESCRIPTION
Refer to page TR±62 for the circuit description.
Code No.
Diagnostic Code Detecting SystemTrouble Area
(1) Main oxygen sensor voltage is 0.45 V or less (lean) for 90 sec. under conditions
(a) and (b).
(2 trip detection logic)
*2
(a) Coolant temp.: 70 °C (158 °F)
or more.
(b) Engine speed: 1,500 rpm or more.
Open or short in main oxygen sensor
circuit
Main oxygen sensor
Ignition system
ECU
25
(2)*1 Difference of air±fuel ratio feedback
compensation value between front (No.
1 3 cylinders) and rear (No. 4 6
cylinders) is more than 15 percentage
for 20 sec. or more under conditions (a)
and (b).
(2 trip detection logic)
*2
(a) Engine speed: 2,000 rpm or more.
(b) Coolant temp.: Between 60 °C
(140 °F) and 95 °C (203 °F).
Open and short in injector circuit.
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction (skipping
teeth of timing belt)
Ignition system
Compression pressure (foreign object
caught in valve)
Air flow meter (air intake)
ECU
(3)*1 Engine speed varies by more than 15
rpm over the preceding crank angle period
during a period of 20 sec. or more under
conditions (a) and (b).
(2 trip detection logic)
*2
(a) Engine speed: Idling
(b) Coolant temp.: Between 60 °C
(140 °F) and 95 °C (203 °F).
Open and short in injector circuit.
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction (skipping
teeth of timing belt)
Ignition system
Compression pressure (foreign object
caught in valve)
Air flow meter (air intake)
ECU
26*1
(1) Difference of air±fuel ratio feedback
compensation value between front (No. 1
3 cylinders) and rear (No.4 6 cylinders) is
more than 15 percentage for 20 sec. or
more under conditions (a) and (b).
(2 trip detection logic)
*2
(a) Engine speed: 2,000 rpm or more.
(b) Coolant temp.: Between 60 °C
(140 °F) and 95 °C (203 °F).
Open and short in injector circuit.
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction (skipping
teeth of timing belt)
Ignition system
Compression pressure (foreign object
caught in valve)
Air flow meter (air intake)
ECU
261
(2) Engine speed varies by more than 15
rpm over the preceding crank angle peri-
od during a period of 20 sec. or more un-
der conditions (a) and (b).
(2 trip detection logic)
*2
(a) Engine speed: Idling
(b) Coolant temp.: Between 60 °C
(140 °F) and 95 °C (203 °F).
Open and short in injector circuit.
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction (skipping
teeth of timing belt)
Ignition system
Compression pressure (foreign object
caught in valve
Air flow meter (air intake)
ECU
*1: Only for USA specification vehicles.
*2: See page TR±25.
TR±70
±
ENGINE TROUBLESHOOTING Circuit Inspection
WhereEverybodyKnowsYourName

Page 3687 of 4087

LEXUS SC400 1991 Service Repair Manual
CIRCUIT DESCRIPTION (Contd)
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

Page 3688 of 4087

LEXUS SC400 1991 Service Repair Manual
DIAGNOSTIC CHART
Check voltage of terminal VF.
Repair or replace harness or
connector.
Repair or replace.
Repair or replace.
Replace main oxygen sensor.
Repair or replace.
Repair or replace.
Replace

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