Code No.B1420: Side-airbag module (RH) (squib) system (short-circuited between terminals of the squib circuit)
| caution |
If diagnosis code B1420 is set in the SRS-ECU, always diagnose the CAN bus lines.
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OPERATION
- The SRS-ECU judges how severe a collision is by detecting signals from the left and right side impact sensors. If the impact is over a predetermined level, the SRS-ECU sends an ignition signal. At this time, if the side-airbag safing G-sensor is on, the SRS side-airbag will inflate.
- The ignition signal is input to the side-airbag module to inflate the side-airbag.
DIAGNOSIS CODE SET CONDITIONS
This diagnosis code is set if there is abnormal resistance between the input terminals of the side-airbag module (RH) (squib).
PROBABLE CAUSES
- Improper engaged connector or defective short spring*
- Short between the side-airbag module (RH) (squib) circuit terminals
- Damaged connector(s)
- Malfunction of the SRS-ECU
| note |
*: The squib circuit connectors integrate a "short" spring (which prevents the air bag from deploying unintentionally due to static electricity by shorting the positive wire to the earth wire in the squib circuit when the connectors are disconnected). (Refer to  ). Therefore, if connector B-109, C-04 or C-04-1 is damaged or improperly engaged, the short spring may not be released when the connector is connected.
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STEP 1. M.U.T.-III CAN bus diagnostics.
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Use the M.U.T.-III to check the CAN bus lines.
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| warning |
Since the radiator fan rotates during CAN bus line diagnostics, make sure that no one is servicing the engine compartment before diagnosing the CAN bus line. Since the CAN communication stops when diagnosing the CAN bus line, the ETACS-ECU detects the time-out of the engine-ECU, and activates the radiator fan to prevent overheating as fail-safe.
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Q.
Is the CAN bus line found to be normal?
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 Go to Step 2.
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 Repair the CAN bus lines (Refer to GROUP 54C, Troubleshooting - Can Bus Diagnosis Table ).
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STEP 2. Check whether the diagnosis code is reset.
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Check again if the diagnosis code is set.
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(1)Erase the diagnosis code.
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(2)Turn the ignition switch to "ON" position.
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(3)Check if the diagnosis code is set.
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(4)Turn the ignition switch to the "LOCK" (OFF) position.
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Q.
Is the diagnosis code set?
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Go to Step 3.
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There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).
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STEP 3. Check SRS-ECU connector B-109, and side-airbag module connector C-04, C-04-1 (M.U.T.-III diagnosis code).
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(1)Disconnect the negative battery terminal.
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(2)Disconnect connectors B-109, C-04 or C-04-1, and then reconnect them.
(3)Connect the negative battery terminal.
(4)Erase the diagnosis code memory, and check the diagnosis code.
Q.
Is diagnosis code B1420 out put?
Go to Step 4.
The procedure is complete. It is assumed that diagnosis code B1420 set because connector B-109, C-04 or C-04-1 was engaged improperly.
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STEP 4. Check the side-airbag module (RH) (M.U.T.-III diagnosis code).
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(1)Disconnect the negative battery terminal.
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(2)Disconnect the side-airbag module connector C-04.
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(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).
(4)
| caution |
Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.
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Insert special tool resistor harness (MB991866) into the C-04 male side connector (SRS-ECU side) by backprobing.
(5)Connect the negative battery terminal.
(6)Erase the diagnosis code memory, and check the diagnosis code.
Q.
Is diagnosis code B1420 set?
Go to Step 5.
Go to Step 6.
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STEP 5. Resistance measurement at the SRS-ECU connector B-109.
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(1)Disconnect SRS-ECU connector B-109.
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(2)
| danger |
To prevent the air bag from deploying unintentionally, disconnect the side-airbag module connector C-04 to short the squib circuit.
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Disconnect side-airbag module connector C-04.
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(3)
| caution |
Insert an insulator such as a cable tie to a depth of 4mm or more, otherwise the short spring will not be released.
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Insert a cable tie [3 mm wide, 0.5 mm thick] between terminals 35 and the short spring to release the short spring.
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(4)Resistance measurement between B-109 harness side connector terminals 12 and 13.
OK: Open circuit
Q.
Is the check result normal?
Go to Step 7.
Repair the harness wires between SRS-ECU connector B-109 (terminal No.12 and 13) and side-airbag module connector C-04 (terminal No.2 and 1).
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STEP 6. Check the side-airbag module (RH) (M.U.T.-III diagnosis code).
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(1)Disconnect the negative battery terminal.
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(2)Disconnect SRS-ECU connector B-109.
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(3)Use a flat-tipped screwdriver to pull out forward and unlock the locking button of the side-airbag module connector (harness side), and then disconnect side-airbag module (RH) connector C-04-1.
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(4)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991884).
(5)Connect special tool resistor harness (MB991884) to the C-04-1 side-airbag module connector (harness side).
(6)Connect the negative battery terminal.
(7)Erase diagnosis code memory, and then check the diagnosis code.
Q.
Is diagnosis code B1420 set?
Replace the air bag harness (RH) (Refer to ).
Replace the side-airbag module (RH) (Refer to ).
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STEP 7. Check whether the diagnosis code is reset.
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Q.
Is diagnosis code B1420 set?
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Replace the SRS-ECU (Refer to ).
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An intermittent malfunction is suspected (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).
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