1991 LEXUS SC400 light

TROUBLESHOOTING
 HOW TO PROCEED WITH 
 TROUBLESHOOTING RS±54 CUSTOMER PROBLEM ANALYSIS CHECK SHEET RS±58 DIAGNOSIS INSPECTION RS±59 SYMPTION SIMULATION RS±65 DIAGNOSTIC TROUBLE CODE MATRIX CHART RS±67 PROBLEM SYMPTOM CHART RS±67 CIRCUIT INSPECTION RS±68 DTC (Normal) RS±68 DTC 11 RS±70 DTC 12 RS±78 DTC 13 RS±85 DTC 14 RS±92 DTC 15 RS±97 DTC 22 RS±102 DTC 31 RS±108 DTC 53 RS±110 DTC 54 RS±115 SRS Warning Light System (Always Lit Up, when ignition switch is Lock position) RS±119 Tc Terminal Circuit RS±121
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HOW TO PROCEED WITH TROUBLESHOOTING
Malfunction symptoms of the supplemental restraint system are difficult to confirm, so the diagnostic
trouble codes become the most important source of information when troubleshoot\
ing. Perform trouble-
shooting of the supplemental restraint system in accordance with the fol\
lowing procedure:
HINT: Do not disconnect the battery negative (±) terminal cable until st\
ep , Diagnostic Trouble Code
Check and Recording, has been completed.

CUSTOMER PROBLEM ANALYSIS
Using the CUSTOMER PROBLEM ANALYSIS CHECK SHEET (See page RS±58) for reference, ask the
customer in as much detail as possible about the problem.
WARNING LIGHT CHECK
Check the SRS warning light. If the light remains on, a malfunction is stored in the center airbag sensor,
assembly, so proceed to step . If the SRS warning light is not on, a malfunction has occurred in the SRS
warning light circuit, so perform troubleshooting for 22.
HINT: 22 is recorded when a malfunction occurs in the SRS warning light syst\
em.
If an open malfunction occurs in the SRS warning light system, the SRS w\
arning light does not light up,
so that until the malfunction is repaired, the diagnostic trouble codes (\
including 22) cannot be confirmed.
 DIAGNOSTIC TROUBLE CODE CHECK AND RECORDING
Check the di agnostic trouble codes and make a note of any malfunction codes which ar\
e output. If a normal
code is output, an abnormality in the power source circuit may have occurred\
, so perform troubleshooting
for source voltage in step .
If 22 is output, skip steps  and  and proceed to step .
 MALFUNCTION CODE CLEARANCE
Clear the malfunction code.
HINT: The malfunction code output in step  indicates that a malfunction has occurred in the circuit desig-
nated by the malfunction code, but does not indicate whether the malfunction \
is still occurring or whether
it was in the past.
Accordingly, it is necessary to find out the present condition of the malfunction oc\
currence by clearing the
malfunction code and performing the diagnostic code check again. If this\
operation is neglected and trou-
bleshooting is performed using only the malfunction code confirmed in step , isolating the problem com-
ponent becomes difficult and invites mistaken diagnosis.
 DIAGNOSTIC TROUBLE CODE CHECK AND RECORDING  SYMPTOM SIMULATION
After repeating ignition switch ON±OFF operation (ON: wait 20 secs, OFF: \
wait 20 secs.) 5 times, check
the diagnostic trouble codes. If any code is output, the malfunction is sti\
ll occurring, so proceed to step .
Bearing in mind that a malfunction code was registered in step , provided that the normal code is present-
ly output, use the methods described in step  to simulate the malfunction.
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10 MALFUNCTION CODE CLEARANCEWhen all the malfunction codes found in steps  and  have been repaired, clear the malfunction codes.
11 DIAGNOSTIC TROUBLE CODE CHECK
After repeating ignition switch ON±OFF operation (ON: wait 20 secs, OFF: \
wait 20 secs.) 5 times, check
the diagnostic trouble codes. If a code is displayed, return to step  and troubleshoot the displayed mal-
function code.
NOTICE: When connecting the battery after clearing the malfunction code, always\
do it with the igni-
tion switch in LOCK position. When the battery has been reconnected, turn the ignition switch to
ACC or ON position after at least 20 seconds have elapsed.
If the battery is reconnected with the ignition switch in ACC or ON posi\
tion, or the ignition switch
is turned ACC or ON within 20 seconds of connecting the battery, it is possible that the diagnosis
system will not operate normally.
12 CONFIRMATION TEST Check the warning light again and confirm that all the malfunctions have been\
repaired. If the warning light
indicates an abnormality, repeat the operation again from step .
RS±56
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SRS WARNING LIGHT CHECK
DIAGNOSIS INSPECTION
(a) Turn the ignition switch to ACC or ON and check that the SRSwarning light lights up.
(b) Check that the SRS warning light goes out after approx. 6
seconds.
HINT:
wWhen the ignition switch is at ACC or ON and the SRS
warning light remains on, the TROUBLESHOOTING
has detected a malfunction code.
w If, after approx. 6 seconds have elapsed, the SRS
warning light sometimes lights up or the SRS warning
light lights up even when the ignition switch is OFF, a
short in the SRS warning light circuit can be considered
likely. Proceed to SRS warning light system (always lit
up when ignition switch LOCK position) on page
RS±119 .
DIAGNOSTIC TROUBLE CODE CHECK
Using diagnosis check wire:
1. OUTPUT DIAGNOSTIC TROUBLE CODE
(a) Turn the ignition switch to ACC or ON position and wait approx. 20 seconds.
(b) Using SST, connect terminals Tc and E of the DLC2. SST 09843±18020
NOTICE: Never make a mistake with the terminal connec-
tion position as this will cause a malfunction.
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2. READ DIAGNOSTIC TROUBLE CODERead the 2±digit diagnostic trouble code as indicated by the
number of times the SRS warning light blinks. As an example,
the blinking patterns; normal, 11 and 31 are as shown on the
illustration.
wNormal code indication
The light will blink 2 times per second.
w Malfunction code indication
In the event of a malfunction, the light will blink. The number
represented by the first blink code output indicates the first
digit of a 2±digit diagnostic trouble code. After a 1.5 second
pause, the second blink code will indicate the second digit.
If there are two or more codes, there will be a 2.5 second
pause between each.
After all the codes have been output, there will be a 4.0 se-
cond pause and they will all be repeated.
HINT:
w In the event of a number of trouble codes, indication will
begin from the smaller numbered code to the larger.
w If it does not output a diagnostic trouble code or output
a diagnostic trouble code without terminal connection,
proceed to the Tc terminal circuit inspection on page
RS±121 .
Using LEXUS hand±held tester: (a) Hook up the LEXUS hand±held tester to the DLC1 or DLC2.
(b) Read 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.
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HINT:

When the SRS warning light remains lit up and the diagnostic trouble code in\
the normal code, this means a
source voltage drop.
This malfunction is not stored in memory by the center airbag sensor assembl\
y and if the power source voltage
returns to normal, after approx. 10 seconds the SRS warning light will automati\
cally go out.

Code 22 in recorded when a malfunction occurs in the SRS warning light syste\
m. If an open malfunction occurs
in the SRS warning light system, the SRS warning light does not light up\
. so that until the malfunction is repaired,
the diagnostic trouble codes (including code 22) cannot be confirmed.

When 2 or more codes are indicated, the lowest numbered code will appear\
first.

If a code not listed on the chart is displayed, then the center airbag s\
ensor assembly is faulty.
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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, theSRS warning light will blink in a 50 m sec cycle to indicate the
codes have been cleared.
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SYMPTOM SIMULATION
ªIntermittent troubles or problemsº 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 pr\
oblems also include complaints about
the SRS warning light going on and off erratically.
The self±diagnostic system stores the circuit of the intermittent pro\
blem in memory even if the ignition switch
is turned off.
And, for accurate diagnosis of the problems, ask the customer to obtain info\
rmation 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.
1VIBRATION 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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