Diagnosis code 28: Passenger’s (Front) Seat Belt Pre-Tensioner (Squib) System Fault 1 (Short Circuit between Terminals of the Squib Circuit)

OPERATION

The SRS-ECU judges how severe a collision is by detecting signals from the front impact sensors and the front air bag analog G-sensor. If the impact is over a predetermined level, the SRS-ECU outputs an ignition signal. At this time, if the front air bag safing G-sensor is on, the pre-tensioner will deploy.

DIAGNOSIS CODE SET CONDITIONS

This diagnosis code is set if there is abnormal resistance between the input terminals of the passenger’s seat belt pre-tensioner (squib).

PROBABLE CAUSES

Improper engaged connector or defective short spring*

Short circuit between the passenger's seat belt pre-tensioner (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). Therefore, if connector C-114 or D-29 <2000> or D-43 <2400> is damaged or improperly engaged, the short spring may not be released when the connector is connected.

DIAGNOSIS PROCEDURE

STEP 1. MUT-II/III diagnosis code

CAUTION

To prevent damage to MUT-II/III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting MUT-II/III.

Turn the ignition switch to the "ON" position.

Check if the diagnosis code is set.

Turn the ignition switch to the "LOOK" (OFF) position.

Q: Is diagnosis code 34 set?

YES: Go to Step 2

.
NO: Go to Step 3

STEP 2. Connector check: SRS-ECU connector C-114

Q: Is connector correctly engaged?

YES: Go to Step 3

.
NO: Engage the connector correctly. Then go to Step 7

STEP 3. Connector check: SRS-ECU connector C-114 and passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400> (Check whether the diagnosis code is reset).

Disconnect the negative battery terminal.

Disconnect connectors C-114 and D-29 <2000> or D-43 <2400>, and then reconnect them. For connector D-29 <2000> or D-43 <2400>, use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.

Connector the negative battery terminal.

Erase the diagnosis code memory, and check the diagnosis code.

Q: Is diagnosis code 28 set?

YES: Go to Step 4

.
NO: The procedure is complete. It is assumed that diagnosis code 28 set as connector C-114 or D-29 <2000> or D-43 <2400> was engaged improperly.

STEP 4. Check the passenger's seat belt pre-tensioner. (Check whether the diagnosis code is reset.)

Disconnect the negative battery terminal.

Disconnect passenger's seat belt pre-tensioner connector D-29 <2000> or D-43 <2400>. Use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.

Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991884).

Connect special tool MB991884 to the D-29 <2000> or D-43 <2400> harness side connector.

Connect the negative battery terminal.

Erase diagnosis code memory, and then check the diagnosis code.

Q: Is diagnosis code 28 set?

YES: Go to Step 5

.
NO: Replace the passenger's seat belt pre-tensioner (Refer to

). Then go to Step 7

STEP 5. Check the passenger's seat belt pre-tensioner circuit at the SRS-ECU connector C-114.

Disconnect SRS-ECU connector C-114.

DANGER

To prevents the air bag from deploying unintentionally, disconnect the passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400> to short the squib circuit.

Disconnect passenger's seat belt pre-tensioner connector D-29 <2000> or D-43 <2400>. Use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.

CAUTION

Insert an insulator such as a cable tie to a depth of 4 mm or more, otherwise the short spring will not be released.

Insert a cable tie [3 mm wide, 0.5 mm thick] between terminals No.27, 28 <except 2400 (RH drive vehicles)>, No.29, 30 <2400 (RH drive vehicles)> and the short spring to release the short spring.

CAUTION

Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.

Check for continuity between C-114 harness side connector terminals No.27 and 28 <except 2400 (RH drive vehicles)>, No.29 and 30 <2400 (RH drive vehicles)>.

OK: Open circuit.

Q: Is the check result normal?

YES: Erase the diagnosis code memory, and check diagnosis code. If diagnosis code 28 sets, replace the SRS-ECU (Refer to

). Then go to Step 7

.
NO: Go to Step 6

STEP 6. Check the harness for short circuit between SRS-ECU connector C-114 (terminal No.27 and 28 <except 2400 (RH drive vehicles)>, No.29 and 30 <2400 (RH drive vehicles)>) and passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400> (terminal No.1 and 2).

NOTE: After inspecting intermediate connector C-117 <2000>, inspect the wiring harness. If the intermediate connector C-117 <2000> is damaged, repair or replace it. Then go to Step 7

Q: Are harness wires between SRS-ECU connector C-114 (terminal No.27 and 28 <except 2400 (RH drive vehicles)>, No.29 and 30 <2400 (RH drive vehicles)>) connector and passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400> (terminal No.1 and 2) in good condition?

YES: Go to Step 7

.
NO: Repair the harness wires between SRS-ECU connector C-114 and passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400>. Then go to Step 7

STEP 7. Check whether the diagnosis code is reset.

Q: Is diagnosis code 28 set?

YES: Return to Step 1

.
NO: The procedure is complete (If no malfunctions are found in all steps, an intermittent malfunction is suspected). Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points


Diagnosis code 28: Passenger’s (Front) Seat Belt Pre-Tensioner (Squib) System Fault 1 (Short Circuit between Terminals of the Squib Circuit)

OPERATION The SRS-ECU judges how severe a collision is by detecting signals from the front impact sensors and the front air bag analog G-sensor. If the impact is over a predetermined level, the SRS-ECU outputs an ignition signal. At this time, if the front air bag safing G-sensor is on, the pre-tensioner will deploy.
DIAGNOSIS CODE SET CONDITIONS This diagnosis code is set if there is abnormal resistance between the input terminals of the passenger’s seat belt pre-tensioner (squib).
PROBABLE CAUSES Improper engaged connector or defective short spring* Short circuit between the passenger's seat belt pre-tensioner (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). Therefore, if connector C-114 or D-29 <2000> or D-43 <2400> is damaged or improperly engaged, the short spring may not be released when the connector is connected.
	DIAGNOSIS PROCEDURE

	STEP 1. MUT-II/III diagnosis code CAUTION To prevent damage to MUT-II/III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting MUT-II/III. Turn the ignition switch to the "ON" position. Check if the diagnosis code is set. Turn the ignition switch to the "LOOK" (OFF) position. Q: Is diagnosis code 34 set? YES: Go to Step 2 . NO: Go to Step 3.
	STEP 2. Connector check: SRS-ECU connector C-114 Q: Is connector correctly engaged? YES: Go to Step 3 . NO: Engage the connector correctly. Then go to Step 7.
	STEP 3. Connector check: SRS-ECU connector C-114 and passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400> (Check whether the diagnosis code is reset). Disconnect the negative battery terminal.
	Disconnect connectors C-114 and D-29 <2000> or D-43 <2400>, and then reconnect them. For connector D-29 <2000> or D-43 <2400>, use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector. Connector the negative battery terminal. Erase the diagnosis code memory, and check the diagnosis code. Q: Is diagnosis code 28 set? YES: Go to Step 4. NO: The procedure is complete. It is assumed that diagnosis code 28 set as connector C-114 or D-29 <2000> or D-43 <2400> was engaged improperly.
	STEP 4. Check the passenger's seat belt pre-tensioner. (Check whether the diagnosis code is reset.) Disconnect the negative battery terminal.
	Disconnect passenger's seat belt pre-tensioner connector D-29 <2000> or D-43 <2400>. Use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.
	Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991884). Connect special tool MB991884 to the D-29 <2000> or D-43 <2400> harness side connector. Connect the negative battery terminal. Erase diagnosis code memory, and then check the diagnosis code. Q: Is diagnosis code 28 set? YES: Go to Step 5. NO: Replace the passenger's seat belt pre-tensioner (Refer to ). Then go to Step 7.
	STEP 5. Check the passenger's seat belt pre-tensioner circuit at the SRS-ECU connector C-114. Disconnect SRS-ECU connector C-114.
	DANGER To prevents the air bag from deploying unintentionally, disconnect the passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400> to short the squib circuit. Disconnect passenger's seat belt pre-tensioner connector D-29 <2000> or D-43 <2400>. Use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.
	CAUTION Insert an insulator such as a cable tie to a depth of 4 mm or more, otherwise the short spring will not be released. Insert a cable tie [3 mm wide, 0.5 mm thick] between terminals No.27, 28 <except 2400 (RH drive vehicles)>, No.29, 30 <2400 (RH drive vehicles)> and the short spring to release the short spring.
	CAUTION Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened. Check for continuity between C-114 harness side connector terminals No.27 and 28 <except 2400 (RH drive vehicles)>, No.29 and 30 <2400 (RH drive vehicles)>. OK: Open circuit. Q: Is the check result normal? YES: Erase the diagnosis code memory, and check diagnosis code. If diagnosis code 28 sets, replace the SRS-ECU (Refer to ). Then go to Step 7 . NO: Go to Step 6.
	STEP 6. Check the harness for short circuit between SRS-ECU connector C-114 (terminal No.27 and 28 <except 2400 (RH drive vehicles)>, No.29 and 30 <2400 (RH drive vehicles)>) and passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400> (terminal No.1 and 2). NOTE: After inspecting intermediate connector C-117 <2000>, inspect the wiring harness. If the intermediate connector C-117 <2000> is damaged, repair or replace it. Then go to Step 7 . Q: Are harness wires between SRS-ECU connector C-114 (terminal No.27 and 28 <except 2400 (RH drive vehicles)>, No.29 and 30 <2400 (RH drive vehicles)>) connector and passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400> (terminal No.1 and 2) in good condition? YES: Go to Step 7. NO: Repair the harness wires between SRS-ECU connector C-114 and passenger’s seat belt pre-tensioner connector D-29 <2000> or D-43 <2400>. Then go to Step 7.
	STEP 7. Check whether the diagnosis code is reset. Q: Is diagnosis code 28 set? YES: Return to Step 1 . NO: The procedure is complete (If no malfunctions are found in all steps, an intermittent malfunction is suspected). Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points .