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RESTRAINT CONTROL SYSTEM 9A1-7
System Schematic
RTW 79ALF000301
SRS Diagnostic System Check
The diagnostic procedures used in this section are
designed to find and repair SRS malfunctions. To get
the best results, it is important to use the diagnostic
charts and follow the sequence listed below:
A Perform the “SRS Diagnostic System Check.”
The “SRS Diagnostic System Check” must be the starting point of any SRS diagnostics. The “SRS
Diagnostic System Check” checks for proper “SRS”
warning lamp operation, the ability of the SRS
control unit to communicate through the “Serial
Data” line and whether SRS diagnostic trouble codes
exist.
B Refer to the proper diagnostic chart as directed b
y
the “SRS Diagnostic System Check.”
The “SRS Diagnostic System Check” will lead you to the correct chart to diagnose any SRS malfunctions.
Bypassing these procedures may result in extended
diagnostic time, incorrect diagnosis and incorrect
parts replacement.
C Repeat the “SRS Diagnostic System Check” afte
r
any repair or diagnostic procedures have been
preformed.
Performing the “SRS Diagnostic System Check” after all repair or diagnostic procedures will ensure
that the repair has been made correctly and that no
other malfunctions exist.
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9A1-8 RESTRAINT CONTROL SYSTEM
Circuit Description
W hen the ignition switch is first turned “ON”, “Ignition 1”
voltage is applied from the “SRS” fuse to the SRS
control unit at the “Ignition 1” input terminals “1”. The
SRS control unit responds by flashing the “SRS”
warning lamp seven times, while performing tests on
the SRS.
Notes On System Check Chart
1. The “SRS” warning lamp should flash seven times after the ignition is first turned “ON”.
2.
After the “SRS” warning lamp flashes seven times, it
should turn to “LOCK”
3. This test checks for the proper operation of the “Serial Data” line. This test will also determine
whether history diagnostic trouble codes are stored
and, if so, identify them.
4. Improper operation of the “SRS” warning lamp is indicated. This test differentiates between ‘a
warning lamp stays “ON” condition’ and ‘a warning
lamp does not come “ON” condition’.
5. This test checks for proper operation of the “Serial Data” line. This test will also identify the stored
diagnostic trouble codes and whether they are
current or history.
Diagnostic Aids
The order in which diagnostic trouble codes are
diagnosed is very important. Failure to diagnose the
diagnostic trouble codes in the order specified ma
y
result in extended diagnostic time, incorrect diagnosis
and incorrect parts replacement.
SRS Diagnostic System Check
Step Action Yes No
1 Note the “SRS” warning lamp as the ignition switch is turned
“ON”.
Does the “SRS” warning lamp flash seven (7) times? Go to Step 2 Go to Step 3
2 Note the “SRS” warning lamp after it flashed 7 times.
Does the “SRS” warning lamp go “OFF”? Go to Step 4 Go to Step 5
3 Note the “SRS” warning lamp as the ignition switch is turned
“ON”.
Does the “SRS” warning lamp come “ON” steady? Go to Chart B. Go to Chart C.
4
1. Note the “SRS” warning lamp as the ignition switch is turned
“ON”.
Ignition switch is at “LOCK”.
2. Connect a scan tool to data link connector.
3. Follow direction given in the scan tool instruction manual.
Ignition switch is “ON”.
4. Request the SRS diagnostic trouble code display, recode all
history diagnostic trouble code(s), specifying as current or
history in repair order.
Is (are) diagnostic trouble code(s) displayed?
Ignition switch
“LOCK”.
W hen DTC B0071 is set, go to DTC B0071 Chart.
For all other history codes refer to
“Diagnostic Aids” For that specific DTC.
A history DTC indicates the
malfunction has
been repaired or is intermittent. SRS is functional
and free of
malfunctions, no
further diagnosis is required.
If scan tool
indicated “NO DATA
RECEIVED,” refer to chassis
electrical section 8.
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RESTRAINT CONTROL SYSTEM 9A1-9
Step Action Yes No
5 1. Ignition switch is at “LOCK”.
2. Connect a scan tool to data link connector.
3. Follow directions as given in the scan tool instruction manual.
4. Ignition switch is “ON”.
5. Request the SRS diagnostic trouble code display, Recode all diagnostic trouble code(s), specifying as current or history in
repair order.
Is (are) diagnostic trouble code (s) displayed? Ignition switch
“LOCK”.
W hen the current DTC is set, go to applicable DTC chart.
And then if DTC B0019, B0025,
B0051, B0055 or
B0071 is set, go to these DTC chart first.
W hen only history
DTCs exist, refer to “Diagnostics Aids” for that specific DTC.
A history DTC indicates the
malfunction has
been repaired or is intermittent. If scan tool indicates
“No Data Received,” refer to chassis
electrical section 8.
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9A1-10 RESTRAINT CONTROL SYSTEM
Chart A SRS Control Unit Integrity Check
RTW 79ALF000301
Circuit Description
W hen the SRS control unit recognizes that “Ignition 1”
voltage, applied to terminals “1”, is greater than 9 volts,
the “SRS” warning lamp is flashed 7 times to verif
y
operation. At this time the SRS control unit performs
“Turn–ON” tests followed by “Continuous Monitoring”
tests. W hen a malfunction is detected, the SRS control
unit sets a current diagnostic trouble code and
illuminates the “SRS” warning lamp. The SRS control
unit will clear current diagnostic trouble codes and move
them to a history file when the malfunction is no longe
r
detected and/or the ignition switch is cycled, except for
DTCs B0051 and B0055.
Chart Test Description
Number(s) below refer to step number(s) on the
diagnostic chart:
1. This test confirms a current malfunction. If no current malfunction is occurring (history DTC set)
the “Diagnostic Aids” for the appropriate diagnostic
trouble code should be referenced. The SRS control
unit should not be replaced for a history diagnostic
trouble code.
2. This test checks for a malfunction introduced into the SRS during the diagnostic process. It is extremel
y
unlikely that a malfunctioning SRS control unit would
cause a new malfunction to occur during the
diagnostic process.
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RESTRAINT CONTROL SYSTEM 9A1-11
3. W hen all circuitry outside the SRS control unit has been found to operate properly, as indicated by the
appropriate diagnostic chart, then and only then
should the SRS control unit be replaced.
Chart A SRS control unit Integrity Check
WARNING: DURING SERVICE PROCEDURES. BE VERY CAREFUL WHEN HANDLING A SRS CONTROL UNIT.
NEVER STRIKE OR JAR THE SRS CONTROL UNIT. NEVER POWER UP THE SRS WHEN THE SRS CONTROL
UNIT IS NOT RIGIDLY ATTACHED TO THE VEHICLE. ALL SRS CONTROL UNIT AND MOUNTING BRACKET
FASTENERS MUST BE CAREFULLY TORQUED AND THE ARROW MUST BE POINTING TOWARD THE FRONT
OF THE VEHICLE TO ENSURE PROPER OPERATION OF THE SRS. THE SRS CONTROL UNIT COULD BE
ACTIVATED WHEN POWERED WHILE NOT RIGIDLY ATTACHED TO THE VEHICLE WHICH COULD CAUSE
DEPLOYMENT AND RESULT IN PERSONAL INJURY
Step Action Yes No
1 1. This chart assumes that the “SRS Diagnostic System Check”
and either a symptom chart or a diagnostic trouble code chart
diagnosis has been performed. W hen all circuitry outside the
SRS control unit has been found to operate properly, as
indicated by the appropriate diagnostic chart, and the
symptom or DTC remains current, check the following.
2. Diagnostic procedures must be performed to verify the need
for SRS control unit replacement.
3. Ignition switch is at “LOCK”.
4. Reconnect all SRS components and ensure all components are properly mounted.
5. Ensure the ignition switch has been in the “LOCK” position for
at least 15 seconds.
6. Note the “SRS” warning lamp as the ignition switch is turned
“ON”.
Does the warning lamp flash 7 times then go “OFF”? The symptom or
DTC is no longer occurring.
Clear SRS
diagnostic trouble codes.
Repeat “SRS
Diagnostic System Check” Go to Step 2
2 Using a scan tool, request the diagnostic trouble code display.
Is the same symptom or DTC occurring that was occurring when
the “SRS Diagnostic System Check” was first performed? Go to Step 3 Ignition switch
“LOCK”.
Go to the
appropriate chart for the indicated malfunction.
3 1. Clear the “SRS Diagnostic Trouble Codes”.
2. Ignition switch is in the “LOCK” position for at least two
minutes.
3. Note the “SRS” warning lamp as the ignition switch is turned
“ON”.
Does warning lamp flash 7 times then go “OFF”? SRS is functional
and free of
malfunctions.
No further
diagnosis is required.
Go to Step 4 Ignition switch
“LOCK”.
Replace SRS control unit.
Go to Step 4
4 Reconnect all SRS components, ensure all components are properly mounted.
Is this step finished? Repeat the “SRS
Diagnostic System Check” —
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Page 5694 of 6020
9A1-12 RESTRAINT CONTROL SYSTEM
Chart B “SRS” Warning Lamp Comes “ON” Steady
RTW 79ALF000301
Circuit Description
W hen the ignition switch is first turned “ON”, “Ignition 1”
voltage is applied from the “METER” fuse to the “SRS”,
warning lamp which is connected to “SRS W arning
Lamp”, terminal “4”. The “SRS” fuses apply system
voltage to the “Ignition 1” inputs, terminals “1”. The
SRS control unit responds by flashing the “SRS”
warning lamp 7 times. If “Ignition 1” is less than 9 volts,
the “SRS” warning lamp will come “ON” solid with no
DTCs set.
Chart Test Description
Number(s) below refer to step number(s) on the
diagnostic chart:
2. This test checks for an open in the “Ignition 1” circuit to the SRS control unit.
3. This test checks for the voltage of “Ignition 1”.
4. This test determines whether the malfunction is a short to ground in the SRS warning lamp circuit.
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RESTRAINT CONTROL SYSTEM 9A1-13
Chart B “SRS” warning lamp comes “ON” Steady
Step Action Yes No
1
1. W hen measurements are requested in this chart use a 5-
8840-0366-0DMM with correct terminal adapter from 5-8840-
0385-0.
2. Ignition switch is at “LOCK”.
3. Connect the scan tool to the data link connector, following
directions as given in the scan tool instruction MANUAL.
4. Ignition switch is “ON”.
5. Request the SRS diagnostic trouble code display.
Does the scan tool indicate “No Data Received”? Go to Step 2 Go to Step 3
2
1. Ignition switch is at “LOCK”.
2. Inspect the SRS control unit harness connector connection to
the SRS control unit.
Is it securely connected to the SRS control unit? Ignition switch
“LOCK”.
Replace SRS control unit.
Go to Step 5 Connect SRS
control unit
securely to de–
activate shorting
clip in SRS control unit harness connector.
Go to Step 5
3 Using scan tool, request the SRS data list.
Is “ignition” more than 9 volts? Go to Step 4 Ignition switch
“LOCK”.
Replace SRS control unit.
Go to Step 5
4
1. Ignition switch is at “LOCK”.
2. Disconnect the SRS coil and the passenger air bag assembly
yellow connector located at the base of the steering column
and behind the glove box assembly.
Disconnect the SRS control unit.
3. Disconnect the connector of the “SRS W arning Lamp” on the
instrument cluster.
4. Measure the resistance on the SRS control unit harness connector as follow.
z From terminals "3" and "23" to ground (ground) (without
the pretensioner)
z From terminals "3" and "15" to ground (ground) (with the
pretensioner and the passenger air bag)
z From terminals "3", "12" and "15" to ground (with the
pretensioner and without the passenger air bag)
Does 5-8840-0366-0DMM display “OL” (Infinite)? Go to Chart A Replace SRS
harness.
Go to Step 5
5 Reconnect all SRS components and ensure all components are
properly mounted.
Is this step finished? Repeat the “SRS
Diagnostic System Check” —
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9A1-14 RESTRAINT CONTROL SYSTEM
Chart C “SRS” Warning Lamp Does Not Come “ON” Steady
RTW 79ALF000301
Circuit Description
W hen the ignition switch is first turned “ON”, “Ignition 1”
voltage is applied from the “METER” fuse to the “SRS”
warning lamp which is connected to the “SRS W arning
Lamp”, terminal “4”. The “SRS” fuse applies system
voltage to the “Ignition 1” inputs, terminals “35”. The
SRS control unit responds by flashing the “SRS”
warning lamp seven times. If “Ignition 1” is more than
16 volts, the “SRS” warning lamp will still be “OFF” solid
with no DTCs set.
Chart Test Description
Number(s) below refer to step number(s) on the
diagnostic chart:
1. This test decides whether power is available to the
SRS control unit warning lamp power feed circuit.
2. This test determines whether the voltage is present
in the warning lamp circuit.
3. This test determines if the malfunction is in the
instrument cluster.
4. This test checks for open in the warning lamp
circuitry.
5. This test isolates the SRS warning lamp circuit and
checks for a short in the SRS warning lamp circuit to
B+.
8. This test checks for a short from the SRS control
unit warning lamp power feed circuit to ground.
9. This test determines whether the short to ground is
due to a short in the wiring.
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