Lexus SC300 / Lexus SC400. Manual - part 481

Main Oxygen Sensors

INSPECTION OF MAIN OXYGEN
SENSORS

1. 

WARM UP ENGINE
Allow the engine to warm up to normal operating tempera-
ture.

2. 

INSPECT FEEDBACK VOLTAGE
Connect the positive (+) probe of a voltmeter to terminal VF1
(for No.1) or VF2 (for No.2) of the check (”DIAGNOSIS”) con-
nector, and negative (–) probe to terminal E1. Perform the
test as follows described on the next page.
HINT: Use SST when connecting between terminals TE1 and
E1 of the check connector.
SST 09843–18020

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EFI SYSTEM

Electronic Control System (Main Oxygen Sensors)

FI–73

Replace the ECU

Zero again

After replacing
the oxygen sensor

Normal

8 times 
or more

Zero

Check the number of times the voltmeter needle fluctuates in 10 seconds

Zero

8 times or more

Warm up the oxygen sensors with the engine at 2,500 rpm
for approx. 120 seconds

Connect terminals TE1 and E1 of the check connector.
And maintain engine at 2,500 rpm

Warm up the engine sensors with the engine at 2,500 rpm
for approx. 120 seconds. And maintain engine at 2,500 rpm.

Check the number of times the voltmeter needle 
fluctuates in 10 seconds.

Less than 8 times

Disconnect terminals TE1 and E1 of the check connector.
And maintain engine at 2,500 rpm.

Measure voltage between terminals VF1 (VF2) and E1.

Less than 8 times

More than 0V

0V

Normal code, code
Nos. 21, 25, and 26

Malfunction code(s)
(Ex. code Nos. 21, 25 and 26

Read and record diagnostic codes. (See TR section)

Repair the relevant diagnostic code

Disconnect terminals TE1 and E1 of the check connector.
And maintain engine at 2,500 rpm.

Read and record diagnostic codes. (See TR section)

Malfunction code(s)
(Ex. code Nos. 21, 25 and 26

Normal code, code
Nos. 21, 25, and 26

Repair the relevant diagnostic code

FI–74

–

EFI SYSTEM

Electronic Control System (Main Oxygen Sensors)

Measure voltage between terminals VF1 (VF2) and E1.

Disconnect terminals TE1 and E1 of the check connector.
And maintain engine at 2,500 rpm.

Measure voltage between terminals VF1 (VF2) and E1.

Disconnect the PCV hose.

0V

5V

More than 0V

Repair (Over rich)

Disconnect the water temp. sensor connector and connect 
resistor with a resistance of 4 – 8 k

Ω

 or another coded water

temp. sensor.

Connect terminals TE1 and E1 of the check connector.

Warm up the oxygen sensors with the engine at 2,500 rpm for 
approx. 120 seconds, and maintain engine at 2,500 rpm

Measure voltage between terminals VF1 (VF2) and E1.

Replace the oxygen  sensor.

Repair (Over  lean)

5V

0V

–

EFI SYSTEM

Electronic Control System (Main Oxygen Sensors)

FI–75

Sub–Oxygen Sensor (USA Spec. only)

COMPONENTS FOR REMOVAL AND
INSTALLATION

FI–76

–

EFI SYSTEM

Electronic Control System (Sub–Oxygen Sensor (USA Spec. only))