Lexus SC300 / Lexus SC400. Manual - part 674

DIAGNOSTIC CHART

DIAGNOSTIC CHART

HINT:

•

When other codes are output in addition to 27 and 29 at the same time, check the circuits for other
codes first.

•

If diag. code 27 is displayed, check left bank sub–oxygen sensor circuit, and if 29 is displayed,
check right bank sub–oxygen sensor circuit.

WIRING DIAGRAM

Check voltage of terminals HTL2, HTR2.

Check resistance of sub–oxygen sensor heater.

Check and repair sub–oxygen sensor heater
circuit.

Check operation of sub–oxygen sensor heater.

Check and replace ECU.

Replace main oxygen sensor.

*: In this case, oxygen sensor can be

deteriorated.

Replace main oxygen sensor.*

TR–84

–

ENGINE TROUBLESHOOTING

Circuit Inspection

NG

OK

OK

NG

INSPECTION PROCEDURE

1

Disconnect the engine & ECT ECU connector.

C

OK

P

(2) Connect the Check Harness A.

(See page 

TR–30

)

(2) Disconnect engine & ECT ECU connector.

(2) Turn ignition switch on.

Measure voltage between terminals HTL2, HTR2 of en-
gine & ECT ECU connector and body ground.

Voltage:

10 – 14 V

Go to step [3].

2

Check sub–oxygen sensor heater.

C

OK

P

Disconnect sub–oxygen sensor connector.

Measure resistance between terminals 1 and 2 of sub–
oxygen sensor connector.

Resistance:

5.1 – 6.3 

 20



C (68



F)

Replace sub–oxygen sensor.

Check and repair harness or connector between
main relay and sub–oxygen sensor, sub–oxygen
sensor and engine & ECT ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–85

NG

OK

3

Check voltage between terminals HTL2, HTR2 of engine & ECT ECU connector and body
ground.

C

OK

Hint

P

(2) Connect engine & ECT ECU connector.

(2) Warm up engine to normal operating temperature.

Measure voltage between terminals HTL2, HTR2 of en-
gine & ECT ECU connector and body ground, when en-
gine is idling and racing at 4,000 rpm.

In the 4,000 rpm racing check , continue engine racing
at 4,000 prm for approx. 20 seconds or more.

Replace sub–oxygen sensor.*

*: In this case, oxygen sensor can be deteriorated.

Check and replace engine & ECT ECU.

TR–86

–

ENGINE TROUBLESHOOTING

Circuit Inspection

–MEMO–

ENGINE TROUBLESHOOTING

TR–87