Lexus SC300 / Lexus SC400. Service manual — part 672

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 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.)

If the malfunction is not detected during idling, perform racing without any load at approx.
2,000 rpm for 30 sec.

HINT: If a malfunction exists, the ”CHECK” 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 Inspection

TR–76

DIAGNOSTIC CHART

DIAGNOSTIC CHART

WIRING DIAGRAM

Refer to page

TR–64

for the WIRING DIAGRAM.

Check and replace ECU.

Repair or replace harness or
connector.

Check compression

Check and replace ECU.

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

Check compression.

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

Check for open and short in harness and
connector.

Check voltage of terminal OX.

Check voltage of terminal VF.

Replace main oxygen sensor.

Repair or replace.

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

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

Replace main oxygen sensor.

Repair or replace.

Repair or replace.

Repair or replace.

TR–77

–

ENGINE TROUBLESHOOTING

Circuit Inspection

NG

Type I

NG

Type II

NG

OK

INSPECTION PROCEDURE

1

Check voltage between terminals VF1, VF2 and E1 of check connector.

C

P

(2) Warm up engine at normal operating temperature.

(2) Connect terminals TE1 and E1 of check connector.

(2) Connect positive prove to terminal VF1, VF2 and

negative prove to terminal E1 of check connector.

(2) Warm up the oxygen sensor by running engine at

2,500 rpm for about 2 minutes.

(2) Then, maintaining engine at 2,500 rpm, count how

many times needle of voltmeter fluctuates between
0 and 5 V

Result:

Go to step [7].

2

Check voltage beween terminals OX1, OX2 and E1 of check connector.

C

OK

Hint

P

Warm up engine at normal operating temperature.

Measure voltage between terminals OX1, OX2 and E1
of check connector when sngine is suddenly raced to full
throttle.

The Voltage should be 0.5 V or higher at least once.

Perform inspection within 1 second

Go to step [7].

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–78

OK

NG

OK

NG

OK

NG

NO

YES

3

Check for open and short in harness and connector between engine & ECT ECU and main oxy-

gen sensor, engine & ECT ECU and check connector (See page

IN–27

).

Repair or replace harness or connector.

4

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

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

TR–132

TR–6

TR–51

TR–13

TR–114

TR–88

TR–68

TR–72

Repair or replace.

5

Check comparession (See page

EM–30

).

Repair or replace.

6

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

Replace main oxygen sensor.

check and replace engine & ECT ECU.

TR–79

–

ENGINE TROUBLESHOOTING

Circuit Inspection