Lexus SC300 / Lexus SC400. Manual - part 792

DIAGNOSTIC TROUBLE CODE
CLEARANCE

Using diagnostic check wire:

(a)  Connect the 2 service wires to terminals Tc and AB of DLC1.
(b)  Turn the ignition switch ACC or ON And wait approx. 6

seconds.

(c)  Starting with the Tc terminal, apply body ground alternately

to terminal Tc and terminal AB twice each in cycles of 1.0
seconds Confirm that body ground is absolute. Finally, keep
applying body ground to terminal Tc.
HINT: When alternately grounding terminals Tc and AB, re-
lease ground from one terminal and immediately apply it to
the other terminal within an interval of 0.2 second. If diagnos-
tic trouble codes do not clear, repeat the above procedure un-
til the codes are cleared.

(d)  Several seconds after performing the clearing procedure, the

SRS warning light will blink in a 50 m sec cycle to indicate the
codes have been cleared.

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SUPPLEMENTAL RESTRAINT SYSTEM

TROUBLESHOOTING

RS–63

Using LEXUS hand–held tester:

(a)  Hook up the LEXUS hand–held tester to the DLC1 or DLC2.
(b)  Clear the diagnostic trouble codes by following the prompts

on the tester screen.
HINT: Please refer to the LEXUS hand–held tester operator’s
manual for further details.

RS–64

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SUPPLEMENTAL RESTRAINT SYSTEM

TROUBLESHOOTING

SYMPTOM SIMULATION

“Intermittent troubles or problems” are the malfunctions about which the customer has a complaint, but which
do not occur and can not be confirmed in the workshop. The intermittent problems also include complaints about
the SRS warning light going on and off erratically.
The self–diagnostic system stores the circuit of the intermittent problem in memory even if the ignition switch
is turned off.
And, for accurate diagnosis of the problems, ask the customer to obtain information as much as possible follow-
ing the customer problem analysis check sheet (See page 

RS–58

) and try to reproduce the intermittent problem.

The problem simulation methods described below are the effective ways for this nature of problem to produce
the problem conditions by applying vibration, heat, and humidity.

1

VIBRATION METHOD: 

When vibration seems to be the major cause.

CONNECTORS

Slightly shake the connector vertically and horizontally.

(Inspection of connectors)

(a) Does the wire harness connecting with its corre-
sponding part have insufficient slack?

(b) Are the terminals dirty?

(c) Are the terminals making loose contact due to termi-
nals spread?

WIRE HARNESS

Slightly shake the wire harness vertically and horizontal-
ly. The connector joint, fulcrum of the vibration, and
body through portion are the major areas to be checked
thoroughly.

PARTS AND SENSORS

Apply vibration slightly by a finger to the part or sensor
considered to be the problem cause and check if the
malfunction will occur.

Caution:

Do not apply vibration to the center

airbag sensor assembly.

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SUPPLEMENTAL RESTRAINT SYSTEM

TROUBLESHOOTING

RS–65

2

HEAT METHOD: When the problem seems to occur when the suspect area is heated.

Heat the component that is likely the cause of the mal-
function with a hair dryer or similar object. Check to see
if the malfunction will occur.

Notice:

Do not heat to more than 60



C (140



F) (Tempera-

ture limit that the component can be touched with a
hand.)

Do not apply heat directly to any part in the ECU.

3

WATER SPRINKLING METHOD:

When the malfunction seems to occur on a rainy day or in
a high–humidity condition.

Sprinkle water onto the vehicle and check to see if the
malfunction will occur.

Notice:

Never apply water directly onto the

electronic components.

HINT:

If the vehicle is subject to water leakage, the leaked
water may contaminate the ECU. When testing a ve-
hicle with a water leakage problem, special caution
must be paid.

4

OTHER: 

When a malfunction seems to occur when electrical load is excessive.

Turn on all electrical loads including the heater blower,
headlights, rear window defogger, etc. and check to see
if the malfunction will occur.

RS–66

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SUPPLEMENTAL RESTRAINT SYSTEM

TROUBLESHOOTING