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Front Seat Removing and Buckle Replacement
 
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Pelican Technical Article:

Front Seat Removing and Buckle Replacement

Nick Czerula

Time:

1 hour1 hr

Tab:

$150

Talent:

***

Tools:

Sockets 13mm 16mm, T50 Torx socket, screwdriver

Applicable Models:

BMW Z3 (1996-02)

Parts Required:

Seat belt buckle

Hot Tip:

Have a friend around to help lift seat

Performance Gain:

Remedy fault code for seat belt pre-tensioner

Complementary Modification:

Clean under seat

Front seat belt buckles in BMW Z3 models are equipped with pyrotechnic automatic pre-tensioners. The pyrotechnic device has an explosive charge, which is triggered by the airbag (MRS) control module in case of sudden deceleration such as a car crash. Once triggered the device cinches up the seat belt by 55 mm (about 2 inches). 

The seat belt pre-tensioner can fail over time and will set a fault code in the airbag control module. If a fault code is set, the airbag warning light will illuminate. To replace this part you have to remove the front seat to access the fastener and wiring harness. If your airbag light is on, you will need a code reader or scan tool to determine what fault code is stored. If you find you have a pre-tensioner fault code, this is a good place to start. You will also need to clear the fault code once the part is replaced; simply replacing the part will not turn off the airbag warning light.

The explosive charge in the seat belt pretensioner poses a hazard if not handled carefully. The front seat belt buckles are bolted to the inside of each front seat. If you aim to remove either front seat, disconnect the negative battery terminal and insulate the end to prevent accidental reconnection.

Interior trim pieces in BMW Z3 cars are often made of preformed hard plastic. Plastic clips or metal screws are used to hold them in place. To avoid marring the trim, work with a plastic prying tool or wrap a screwdriver tip with masking tape before prying out trim panels, switches or electrical accessories.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

In this tech article, I combined the procedures for the front seat belt buckle and the front seat removing, as they are so closely related. 

Move seat all the way back and up to highest position.
Figure 1

Move seat all the way back and up to highest position. Then working at the front of the seat rail, remove both 13mm seat mounting nuts (green arrow).

Next, remove the seat belt from the seat belt bracket on the top of the seat.
Figure 2

Next, remove the seat belt from the seat belt bracket on the top of the seat. Carefully slide it out and place it aside.

Then, move seat all the way forward.
Figure 3

Then, move seat all the way forward. Remove the two 16mm seat mounting bolts from rear seat rails (green arrows).

If your seat wonÃÆ'‚'t move and you are trying to remove it to replace or diagnose a bad motor or switch, you can try to remove the bolts and nuts using a wrench.
Figure 4

If your seat won't move and you are trying to remove it to replace or diagnose a bad motor or switch, you can try to remove the bolts and nuts using a wrench. I say try because it is a challenge. The front nuts can be removed with an open end wrench, there is little room for movement, but with some patience you can get the nuts out. The rear bolts are more challenging, especially the inner bolt because it is tucked under the seat. Try using a short 16mm wrench and loosening the bolts, the hardest part will be breaking them free. I find lever on the wrench end against a block of wood with a pry bar breaks them free. This photo shows removing one of the fasteners using an open end wrench.

Another option for moving a stuck seat is to manually power up the fore and aft motor.
Figure 5

Another option for moving a stuck seat is to manually power up the fore and aft motor. The motor is located at the front of the seat, under the seat cushion (green arrow). Use the steps mentioned later in this article and disconnect the seat motor electrical connectors. This way you have less of a chance or sending power into the vehicle electrical system. With the motor disconnected, us a fuse jumper to battery positive and a jumper to battery negative, then connect the jumpers to the motor. If the motor goes in the wrong direction, reverse your connection. Disconnect battery negative cable. See our tech article on battery installing and connecting.

Now you have to disconnect the electrical connectors under the seat.
Figure 6

Now you have to disconnect the electrical connectors under the seat. Slide the seat forward on the carpet, then tilt it backward. You will see two sets of electrical connectors. One is for the seat motors, one set is for the seat belt buckle. Disconnect the seat motor connectors by squeezing the retaining tabs (green arrows) and pulling the connector straight out. Repeat this step for both connectors. To disconnect the seat belt buckle connector(s), pull the electrical connectors (yellow arrows) straight out and separate. Hold one side steady while pulling the other, this will prevent stressing the harness.

Lift side of seat up and tilt toward opposite side of vehicle.
Figure 7

Lift side of seat up and tilt toward opposite side of vehicle. Use a black of wood (yellow arrow) to hold seat in the position. Avoid letting seat rest on plastic trim, it will scratch it. Remove the seat belt 16mm bolt (green arrow). Lay seat belt aside.

Cover seat rail with a fender cover (yellow arrow).
Figure 8

Cover seat rail with a fender cover (yellow arrow). Then open the convertible top. With the top open, grab the seat back at the bottom between the back and the seat cushion. Lift the seat out of the vehicle. Be careful not to scratch the body or trim when removing.

With seat on floor, disconnect seat belt pre-tensioner electrical connector by pulling it straight up.
Figure 9

With seat on floor, disconnect seat belt pre-tensioner electrical connector by pulling it straight up.

Remove wiring harnesses (green arrows) from seat by feeding it through the seat cushion fabric at rear.
Figure 10

Remove wiring harnesses (green arrows) from seat by feeding it through the seat cushion fabric at rear.

Then remove T50 Torx seat belt buckle fastener (green arrow).
Figure 11

Then remove T50 Torx seat belt buckle fastener (green arrow). Remove seat belt buckle with pre-tensioner from seat. This is a good chance to clean the side of your seat. There may be stains or a bunch of debris on rail like our subject vehicle.

Install new seat belt buckle and tighten fastener.
Figure 12

Install new seat belt buckle and tighten fastener. Check that seat belt buckle cutout is engaged with steel dowel on seat (green arrows). Be sure to properly route wiring harness and confirm pre-tensioner electrical connector is properly seated. Lift seat into vehicle, then reconnect electrical connectors. Install seat and seat belt fasteners and tighten. If you had a fault code for the pre-tensioner, now is the time to clear it.

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Comments and Suggestions:
genki Comments: i have a 98 z3 and changing out the seats with what i know to be M sport seats in very nice condition...not replacing the seat belts...do i have to working about the seatbelt explosive devices...will undoing the negative lead on the battery and then reataching it take care of it?
October 18, 2016
  Followup from the Pelican Staff: Yes, do exactly that. Remove the negative terminal and reconnect it when done. DO not connect it while the components are out, a fault code may be set. - Nick at Pelican Parts  
Mikey Comments: Most of this is also applicable to the 318ti. Thanks for this, it really helped!
October 13, 2016
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
tonyb Comments: on my 1997 Z3 there is a redundant wire, I guess its for a seat belt buckle connected warning system? To test the pyrotechnic device, meter the resistance across the two pins to device. Should be around 2-3 ohms.
December 10, 2015
  Followup from the Pelican Staff: NEVER test resistance across a, airbag component. The voltage from your meter could trigger the part, injuring you or someone around you. - Nick at Pelican Parts  
Phil Comments: Is the the correct repair for a code on a 1997 Z3 1.9 that says the fault is "seat belt buckle switch, passenger"?
November 11, 2015
  Followup from the Pelican Staff: Yes, unless of course the wiring to the seat belt buckle is damaged. - Nick at Pelican Parts  
Torch Comments: Thank you so much for seat removal instructions.
November 8, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Frankie Comments: Thank you so much.Very helpful.
June 13, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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Page last updated: Wed 12/7/2016 02:07:24 AM