I have a 2012 Infiniti G37x with 95,000 kilometres on it. (Canada).

As you know, under hard decelaration (panic braking almost), the seat belts will tighten up automatically via some sort of motor and pull the seat belt taut in order to take up any slack in the seat belt which could harm the occupants in a collision.

Recently, my car is doing this under just moderate braking. Normally, the car never did this. Now, a moderate application of the brake applies the seat belt pre-tensioner (100 percent of the time), and it reels you back into the seat in a real hurry. It's very uncomfortable. I took it to the dealer that I bought the car from and initially they told me the brakes needed bleeding. I was skeptical about that, but figured that flushing the brake hydraulic system would not be money down the drain. Well, it didn't work. (My spidy senses told me that it wouldn't work.)

It's a long story, but they are proposing more work (and cost) that seem pointless to me. I will explain in greater detail later as I'm strapped for time right now.

But what I'd like to know from everyone out there is, "has anyone on this forum had the problem where all of a sudden your car's seat belt pretensioner started actuating under moderate / normal braking?"

If so, what was the cause.

Cause right now, my dealer is just throwing ideas at the wall.

Thanks

 

^^
I previously had a 2012 G37S 6 speed and never noticed that problem. Then again my driving style rarely required any of the panic braking that you describe.
Perhaps you should just readjust your driving style to avoid panic braking by speeding?
The seat belts are designed to prevent your body and head from striking the windshield allowing you to live another day.
Just my $.02

 

Perhaps you should learn to read.

Because if you knew how to read you would have understood that what I said in my post above was that this problem is now occurring under MODERATE braking. And you would have understood that this is outside the normal performance characteristics of the car and is a new perforformance issue with the car. You would also have known that nowhere did I state that I was speeding.

Just my $0.02.

 

A seatbelt pretensioner cannot be used more than one. It's an explosive charge that releases a backward winding spring, one shot and it's done. It will pull you VERY HARD into the seat and the seatbelt is 100% non functional after it strikes. This is actuated by the SRS diagnostic module in conjunction with the airbags deploying based on which collision sensors were tripped.

What you're probably feeling is the automatic lockup on a seatbelt if you pull on it really hard, there is basically a "ball on a pendulum" that "swings forward" when you jam on the brakes and engages the lock on the seatbelt which causes it to no longer extend, it has to be released/retracted back into the seat belt winder to get the pendulum to swing back to the start position.

I'm guessing your seatbelt lockup has failed and is jammed to one side and isn't resetting properly. Try pulling the seatbelt out ALL THE WAY until there is no seatbelt left whatsoever and then letting it quickly retract back into the winder.

If that doesn't work you probably need to remove the trim panel over the winder and spray it with some silicone spray.

 

Nope, its a motor that tightens the seatbelt under (usually) more extreme braking. You can actually hear the whir of the motor. It probably reels in about 2 inches of seat belt slack to pull you back in the seat.

It reels in both front belts simultaneously and then holds in the locked position for maybe 7 seconds, then automatically releases and resets. In an average about town trip, say 10 km, it will deploy and reset 5 or 6 times. Its uncomfortable, annoying and fills you with a bit of dread every time you hit the brakes.

Its definitely a motor.

The motor is.located in the B post in the seatbelt reel i believe.

I may be using the wrong term when I say "seat belt pretensioner". It may have a different name, but it is an electric motor that applies tension to the seat belt normally under panic braking (like traffic in front of you suddenly brakes and you hammer on the brakes to avoid plowing into the guy in front of you), but in my case has recently taken to acctuating fairly regularly.

The dealer in his description on the work order did not write it up as "seat belt pretensioner" but in fact just wrote it up as "seat belt tightening" and verified the problem. His first suggestion was to bleed the brakes, and I agreed to that course of action (even though I had my doubts that the brakes needed bleeding), however, that did not fix the problem. His subsequent reccomendation was many items - replace the front brakes and rotors, a valve in the brake hydraulic system, an abs module, a g force sensor, brake pedal adjustment (seiously) and 2 or 3 other items. That's where I drew the line because he doesn't know how to fix the problem. He's just going through everything that maybe could be wrong (and charging me one after the other until maybe he gets it). I don't like that course of action because they won't credit you for the needless work. Any fool can just replace one thing after the other until you find it. By bringing it to the dealer, I was figuring that he had seen this problem before and would know the problem, or that he could at least diagnose the problem and zero in on it. That does not appear to be the case. I'm surprised, very surprised in fact at that. In fact, the mechanic who wrote up the subsequent diagnostic report put "straight time" in his report. Meaning that this (and by default me) is viewed as a bottomless pit of money.

I just dropped 2 grand on the car on Friday (rear brakes, serpentine belt, oil change, engine air filter, brake bleed, fuel injector service) I can see this seat belt issue costing me another 2 to 3 grand in a heart beat. I'm cautious. The car is 8 years old, but only has 95 thousand kilometres on it and has not been driven hard. Though it is parked outside. I questioned the service advisor on their approach and what I was told was that they have a flow chart in the service manual and they are following that flow chart.

I've googled it and there is some information on line about this problem. But its not definitive and its scant. One guy on line stated that he changed the front brakes and the problem was corrected. The mechanic did recommend changing the front pads and rotors, but I declined that because I changed the pads and rotors myself 2 years and less than 20,000 km ago. He said there was 4 mm of pad left. 4 mm is a fair bit of pad left. Given the rears just cost me 725 plus tax, the fronts will be the same-ish. I agreed for him to do the rears because he reported 1 mm of pad left and he had the car, but the fronts had lots of pad left and 'rusty rotors" are normal (he took a photo of the outside edge of the rotor as example of being rusty. Of course it rusts, its bare cast iron and it is not swept by the pads.) In addition, he (the mechanic) recommended a new oil pan and transmission pan because they are rusty too. At 600 and 800 plus tax respectively. That was also declined as was the cabin microfilter because I changed that myself last Christmas and its a 10 minute job. I will put the car on stands and crawl underneath next week to verify the extent of the corrosion in the oil pan and transmission pan.

I'm now taking this problem on myself because I've dropped enough money at the dealer.

The first step is on line forums like this to see if others have had the same problem. Also, reading the service manuals myself to see what they say and checking the front brakes myself
and replacing if necessary and the recommended course of action.

 

Ok I just realized you posted in the G37 section, I should have realized this when you described the issue but there's VERY little G37 activity here on the G35DRIVER site. Most folks post over on MY37.

You do NOT have the striker fired pre-tensioner, you are correct it's a motorized pre-tensioner. The system is INCREDIBLY basic though and I don't know why the dealership can't figure out the issue.

Here's how it works basically, there is a brake pedal stroke sensor, it just measures travel of the brake pedal and sends a signal back to the pre-crash seat belt control unit. If the brake pedal is depressed far enough then the control unit begins to wind the motor for the front seats, left and right seat are controlled independently and if the seat belt is not engaged (there is a switch so the control unit knows) then that seat's winder will not activate.

This is why most folks are able to fix the issue by changing the brakes or bleeding the brakes, if the pedal has too much travel to engage the brakes then it's going to start activating the pre-tensioning system because that brake pedal stroke sensor doesn't know the difference, it just measures how far the brake pedal is being depressed.

If your brake pedal is nice and firm and doesn't have extra travel I would start by replacing the pedal stroke sensor, check out this eBay listing so you can see what the sensor looks like. Verify that it's actually bolted in place properly and didn't lose one of the mounting screws, also there is a slight amount of adjustment on the switch so you might be able to just loosen the bolts and reposition it slightly. You can see from the picture that the bolt holes are oblong and allow for some play. Also work the switch manually by hand and make sure that little travel arm is nice and smooth and doesn't bind up or feel wierd.

EDIT: This sensor is located up on the arm for the brake pedal under the dash.

https://www.ebay.com/itm/OEM-Pedal-T....c100005.m1851

Internally that switch works almost exactly like the APP accelerator pedal position switch, there are basically two rheostats, one sends a signal that scales from 0 to 5 volts, the other sends a signal that scales from 5 to 0 volts. They are inverse from each other, the computer looks at both signals to verify the switch is functioning properly.

If the brake pedal feels nice and solid and you don't think the brakes need bled, and the switch appears to be functioning normally and has been replaced, then the next logical step would be to replace the pre-crash seat belt control unit. This is NOT the SRS diagnostic module, it's a separate computer behind the glove box and it's only purpose is the seat belt winding motor. Remove the glove box and you can see it. Here is an ebay listing of a control unit so you can see what it looks like. I don't think they required any kind of programming, simply plug-and-play. Also I think they were mostly a generic item and didn't need to be an EXACT part number match but you should try to get an exact match if one is available.

https://www.ebay.com/itm/08-09-2008-...Cclp%3A2334524

When replacing any electrical components including that pedal switch it's good practice to disconnect the battery.

 

Read the content of the service manual on seat belts. It is the link below.

https://www.nicoclub.com/service-man...an/2012/SB.pdf

 

If your brake pedal does NOT feel very solid and you think there's extra play or you are depressing it further than it should then start first by bleeding the brakes. G37 have the same weird bleed order as the G35, it's not your standard "furthest wheel to closest wheel" bleed order.

Rear right - front left - rear left - front right

If it still has extra play / overtravel after bleeding the brakes then your brake master cylinder likely needs replacement.

Personally I like using a Motiv bleeder, quick and easy one man brake bleeding without all that hassle of pumping up the brake pedal.

 

That's not the correct book, he wants SBC - Seat Belt Controls, not SB - Seat Belt.

 

That's perfect. Thanks for your help.

I did some google searching last week when the dealer called me to tell me that they had a very long list of what could be wrong. (They started with bleeding the brakes, then that didn't work. They stated that the mechanic had reported that the brake pedal felt soft. I had never noticed a soft brake pedal. (But to be honest, the Infiniti brake pedal never struck me as rock solid either from new.) They also claimed they felt a pulsation in the brakes, which again might cause the caliper pistons to be pushed ever so slightly back in the bore resulting in increased brake travel). Again, I had not noticed a brake pulsation. And I am a hound for any unusual "feel" to any car I drive. I am tuned into smell, noise, feel when I am driving.) But never the less, I have just purchased new OEM rotors and pads and will do that work myself. From my google searching, I became aware of the brake pedal travel sensor you mentioned. And I could see that the holes in the sensor were slotted allowing some adjustment. What I didn't know until your post was whether or not that brake travel sensor was interlocked to the air bag system. Last thing I want to do is clock that sensor a bit too much and ka-boom when I hit the brakes.

I was not aware of the control unit behind the glove compartment until I read your post, so thanks very much for that.

Right now in Toronto, there is a bit of snow on the ground and it's should melt later this week which will allow me to remove and replace the front brakes on the weekend. (I have to work in the mutual driveway at my house because I cannot fit the car between the houses to work in my garage.) So this weekend, I plan to RnR my front brakes, check for the alleged corrosion to the oil pan, replace the cabin air filter and install the snow tires. If the brake work doesn't solve the problem, I will take a look at that brake travel sensor.

Also, the dealer told me that the car has a "g-force sensor" that works in tandem with the brake pedal (he never mentioned the brake travel sensor though). I thought that made sense because what if the driver didn't see it coming and did not apply the brakes to actuate the seat belt tensioner? You post would imply no such g-force sensor. Unless the control module does that.

I will report back what results from my planned work this weekend coming.

 

I hope not.

And usually my wife flies the brake pedal while run back and forth between the bleeders and the Master cylinder.

 

The "g-force sensor" they're talking about is actually a YAW SENSOR located below the center console, it's not related to the SRS or pre-crash system. It just detects if the vehicle is rotation (spinning like if you're sliding on ice), it measures against the steering angle sensor and if there is a difference between steering angle and yaw rotation then the Vehicle Dynamic Control (VDC) begins to automatically pulse the brakes on specific corners of the car to bring you out of a spin.

There will be a light on the dash that says VDC/SLIP, VDC is when it's actively working brakes to control spin, SLIP is when it's limiting throttle because one or more wheels are not sending the same wheel speed data back via the independent wheel speed sensors.

I think the G37 uses the same style of initialization on the system, when you start the car roll down the driver window and listen carefully for a faint "grinding" sound coming from the engine bay on the driver side, there is an ABS motor that turns on for 1 second when the vehicle first reaches 10mph (convert that to KM). That's how the VDC system works, you don't have to have your foot on the brakes to generate fluid pressure because it has it's own motor to make pressure. When the VDC system is on the motor will be on as well.

I doubt any of these systems are causing your problem though because the light on the dash WILL BE ON anytime the VDC/SLIP systems are engaged.

 

Hey, Did you ever get this figured out? This started happening to my 08 G35 after I had stainless steel brake lines installed. I figure since there's less give in the system the sensor now thinks more moderate braking is emergency braking. Anyone know if there's any adjustment capability? Thanks!

 

Yes, I sorted it out. I replaced the brakes - rotors and pads and the problem is MUCH better.

Note, I bought new OEM rotors and pads from Infiniti. When I went to "Downtown Infiniti" the parts guy asked me if I wanted standard pads, or uprated pads. This was the first time I'd ever been asked that, but I elected for the supposedly better pads. They were made by Mitsubishi if I recall correctly. Anyway, they were a BEAR to install. They were incredibly tight to fit into the front brake pad cradle (at least that's what I call it. It's a cast piece that bolts up to the front suspension that contains these brass clips. The pads have tabs on them that have to slip into the brass clips. It was impossible to get the pads into the clips. They were almost there, but not quite. (And yes, I bought the hardware kit too. Didn't matter old or new, same problem.) The solution was to take a metal file and gently file the tabs until they slid into the brass clips properly. Not something I would have expected.