Code No.B1634 Knee air bag module (squib) system (shorted to squib circuit
power supply) <Vehicles with rear curtain air bag>
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- If diagnosis code B1634 is set in the SRS-ECU, be sure to diagnose the
CAN bus line.
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Only when the frontal impact exceeding the
threshold is simultaneously detected (turned ON) by the front impact sensor
as well as by the analogue G-sensor and safing G-sensor in SRS-ECU, the
electric current is supplied from SRS-ECU to the knee air bag module
(squib).
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The code is set when the input terminal of
SRS-ECU knee air bag module (squib) shorted to power supply.
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- Damaged wiring harness and connectors
- Knee air bag module (squib) harness shorted to power supply
- Malfunction of SRS-ECU
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STEP 1. M.U.T.-III CAN bus diagnostics.
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Use M.U.T.-III to diagnose the CAN bus
lines.
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Q.
Is the check result normal?
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 Go to Step 2.
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 Repair
the CAN bus line (Refer to GROUP 54C - Troubleshooting  ).
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STEP 2. Check whether the diagnosis code is set again.
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(1)Connect the negative battery terminal.
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(2)After erasing the diagnosis code memory, check the
diagnosis code again.
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(3)Disconnect the negative battery terminal.
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Q.
Is diagnosis code No. B1634 set?
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Go to Step 3.
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Intermittent malfunction (Refer to
GROUP 00 - How to Use Troubleshooting/Inspection Service Points
- How to Cope with Intermittent Malfunction).
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STEP 3. Diagnosis check by dummy resistor connection.
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(1)Check that the negative battery terminal is disconnected.
If the negative battery terminal is connected, disconnect it.
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(2)Use the flat-tipped screwdriver to pull out
the locking button of wiring harness side connector, and release the
lock.
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(3)Connect the dummy resistor (Special tool:
MB991865) to the resistor harness (Special tool: MB991884).
(4)Connect
the resistor harness (special tool) to right curtain air bag module
connector.
(5)Connect the negative battery terminal.
(6)After erasing
the diagnosis code memory, check the diagnosis code again.
Q.
Is diagnosis code No. B1634 set?
Go to Step 4.
Replace the knee air bag
module.
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STEP 4. Voltage measurement at the SRS-ECU connector.
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(1)Check that the negative battery terminal is disconnected.
If the negative battery terminal is connected, disconnect it.
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(2)While pushing the part "A" indicated in the
figure of the harness side connector, turn the lock lever to the direction
of the arrow to release the lock lever. After disconnect the SRS-ECU
connector.
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(3)
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To release the connector short spring in the
following operations, disconnect this harness side connector, and keep
the squib circuit shorted.
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Slide the outer housing of harness side connector in the arrow
direction shown, and disconnect the harness side connector.
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(4)
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The short spring may not be released due to the
insufficient insertion. Therefore, insert the insulator for 4 mm or
more.
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Insert an insulator (width: 3 mm, thickness: 0.5 mm) such as cable
tie between the KDS+, KDS- line, and then release the short
spring.
(5)Connect the negative battery terminal.
(6)Ignition switch:
"ON"
(7)Take the measurements below at the harness side
connector.
OK: 1 V or less
(8)Disconnect the negative
battery terminal.
Q.
Is the check result normal?
Go to Step 5.
Repair the wiring harnesses
KDS+, KDS- line between the SRS-ECU connector and the knee air bag
module connector.
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STEP 5. Check whether the diagnosis code is set again.
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Q.
Is diagnosis code No. B1634 set?
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Replace SRS-ECU.
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Intermittent malfunction (Refer to
GROUP 00 - How to Use Troubleshooting/Inspection Service Points
- How to Cope with Intermittent Malfunction).
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