Lexus SC300 / Lexus SC400. Manual - part 673

OK

NG

OK

NG

NO

YES

7

Check each item found to be a possible cause of problem.

Check each ciruit found to be a possible cause of trouble according to the results of the check in 1. The
numbers in the table below show the order in the which the checks should be performed.

 

TR–132

 

TR–6

 

TR–51

 

TR–13

 

TR–114

 

TR–88

 

TR–68

 

TR–72

 

TR–72

Repair or replace.

8

Check compression (See page 

EM–30

).

Repair or replace.

9

Does malfunction disappear when a good main oxygen sensor is installed?

Replace main oxygen sensor.

Check and replace engine & ECT ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–80

–MEMO–

TR–81

ENGINE TROUBLESHOOTING

Diag. Code  27, 29

Sub–Oxygen Sensor Circuit

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–62

.

Code No.

Diagnostic Code Detecting Condition

Trouble 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–oxygen

sensor

Sub–oxygen sensor heater.

ECU

27

29

(2) Main oxygen sensor signal is 0.45 V or more and

sub–oxygen sensor signal is 0.45 V or less 

under sonditions (a) and (b).

(2 trip detection logic) *

(a) Coolant temp.: 80

°

C (176

°

F) or more.

(b) Accel. pedal: Fully depressed for 2 sec. or

more.

Open or short in sub–oxygen sensor circuit.

Sub–oxygen sensor

ECU

*: See 

page 

TR–21

.

HINT: 

Diag. code 27 is for the left bank sub–oxygen sensor circuit. 
Diag. code 29 is for the right bank sub–oxygen sensor circuit.

TR–82

–

ENGINE TROUBLESHOOTING

Circuit Inspection

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 confirming that diag. code

is no longer detected.

Malfunction: Open or Short in Sub–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.



With the A/C ON and the transmission in D range (O/D OFF), drive at 40 –60 mph (64–96
km/h) for 6 min.



After the driving in , stop the vehicle.



Once the vehicle is stopped, within the next minute apply acceleration with the throttle
fully open for 4 sec.

HINT:  If a malfunction exists, the ”CHECK” engine warning light will light up after full acceleration

for 4 sec.

NOTICE: 

If the conditions in this test are not strictly followed, detection of the malfunction
will not be possible.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–83