code 32 LEXUS SC300 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 to the coolant temperature.
The lower the coolant temperature, the greater the
thermistor resistance value, and the higher the coolant
temperature, the lower the thermistor resistance value
(See Fig. 1.).
The water temperature sensor is connected to the ECU
(See next page). The 5 V power source voltage in the
ECU is applied to the water temperature sensor from the
terminal THW via a resistor R. That is, the resistor R and
the water temperature sensor are connected in series.
When the resistance value of the water temperature
sensor changes in accordance with changes in the cool-
ant temperature, the potential at the terminal THW also
changes. Based on this signal, the ECU increases the
fuel injection volume to improve driveability during cold
engine operation. If the ECU records the diagnostic
code 22, it operates the fail safe function, keeping the
coolant temperature at a constant 80 5C (176 5F).
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ENGINE TROUBLESHOOTING Circuit InspectionTR±68
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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) are output\
simultaneously, E2 (sensor ground)
may be open.
WIRING DIAGRAM
Check and replace ECU. Repair or replace harness or con-
nector.
Replace water temp. sensor.
Check voltage of sensor.
Check resistance of sensor.
Check for open and short in harness and
connector between ECU and water temp. sensor. Check for momentary interruption
(See page
TR±23).
TR±69±
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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) are output simultane\
ously, E2 (sensor ground) may be open.
1Check voltage between terminals THW and E2 of engine & ECT ECU connector\
.
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Turn ignition switch on.
Measure voltage between terminals THW and E2 and
engine & ECT ECU connector.
Check for momentary interruption
(See Page TR±23).
2Check water temp. sensor.
C
OK
PDisconnect the water temp. sensor connector.
(See page FI±99).
Measure resistance between terminals.
Resistance is within Acceptable Zone on chart.
Replace water temp. sensor.
3
Check for open and short in harness and connector between engine & ECT ECU and\
water temp.
sensor (See page IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
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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
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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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Diag. Code 24Intake Air Temp. Sensor Circuit
CIRCUIT DESCRIPTION
The intake air temp. sensor is built into the air flow meter and senses the\
intake air temperature.
The structure of the sensor and connection to the ECU is the same as in the\
water temp. sensor shown on page
TR±68.
If the ECU records the diagnostic code º24º, it operates the fail \
safe function, keeping the intake air temperature
at a constant 20 5C (68 5F).
Code No.Diagnostic Code Detecting ConditionTrouble Area
24Open or short in intake air temp. sensor circuit
for 0.5 sec. or more.
Open or short in intake air temp. sensor circuit.

Intake air temp. sensor

ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: If diagnostic codes º22º (water temperature sensor circuit), º\
24º (intake air temperature sensor
circuit) and º41º (throttle position sensor circuit) are output simultaneousl\
y, E2 (sensor ground) may
be open.
WIRING DIAGRAM
Check and replace ECU. Replace water temp. sensor.
Check for momentary interruption
(See page
TR±23).
Repair or replace harness or
connector.
Check voltage of sensor.
Check resistance of sensor.
Check for open and short in harness and
connector between ECU and water temp. sensor.
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Diag Code

25Air±Fuel Ratio Lean Malfunction
Diag. Code
26Air±Fuel Ratio Rich Malfunction
CIRCUIT DESCRIPTION
Refer to page TR±62 for the circuit description.
Code No.Diagnostic Code Detecting ConditionTrouble 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)*
(a) Coolant temp.: 60 5C (140 5F) or more.
(b) Engine speed: 1,500 rpm or more.
Open or short in main oxygen sensor circuit

Main oxygen sensor

Ignition system

Water temp. sensor
25 V
26
(2) Main oxygen sensor voltage is alternating above and below 0.45 V at 5 times par
second or more under conditions (a) and (b).
(2 trip detection logic)*
(a) Engine speed: Idling
(b) Coolant temp.: Between 60 5C (140 5F)
and 95 5C (203 5F)

Open or short in injector circuit.

Fuel line pressure (injector blockage)

Air flow meter (air intake)

Engine ground bolt loose

Foreign object caught in valve
(3) Difference of air±fuel ratio feedback compensation
value between right and left banks is more than 10
percentage for 30 sec. or more under conditions (a)
and (b).
(2 trip detection logic)*
(a) Engine speed : 2,000 rpm or more.
(b) Coolant temp.: Between 60 5C (140 5F)
and 95 5C (203 5F)

Fuel line pressure (injector leak, blockage)

Mechanical system malfunction
(skipping teeth of timing belt)

Ignition system
*: See page TR±21.
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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±
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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.
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Diag. Code 27Sub±Oxygen Sensor Circuit (Only for
USA spec.)
CIRCUIT DESCRIPTION
The sub±oxygen sensor is installed on the exhaust pipe. Its construction\
and operation is the same
as the main oxygen sensor on page TR±60.
Code No.
Diagnostic Code Detecting ConditionTrouble Area
(1) Open or short in heater circuit of sub± oxygen sensor for 0.5 sec. or more.
Open or short in heater circuit of sub±oxy-
gen sensor.
 Sub±oxygen sensor heater.
 ECU
27
(2) Main oxygen sensor signal is 0.45 V or
more and sub±oxygen sensor signal is
0.45 V or less under conditions (a) (c).
(2 trip detection logic) *
(a) Coolant temp.: 80 °C (176 °F)
or more.
(b) Engine speed: 1,500 rpm or more.
(c) Accel. pedal: Fully depressed for 2 sec. or more.
Open or short in sub±oxygen sensor cir-
cuit.
 Sub±oxygen sensor
 ECU
* : See page TR±25.
TR±76
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