XC90 Seat Belts

[Paulj1]

Hello peeps, I have a March 2016 XC90 T8, love it great car. About a year ago, i had a seatbelt warning come on the dash, dealer said the seatbelt unit needs replacing, £600 please, i said no way, they replaced it under warranty.

Dealer said that the active seatbelts had deployed more than 50 times, unit has life of 50 activiations, so needs replacing.

Now i did used to drive over a few humps to make it activate, to scare the kids, so i stopped that.

A year on, in for service yesterday, asked them to check, they say its activated 35 times...no way......

I did get technical repsonse below from volvo, on how the system works, I cannot see how the hell this is happening, i live in a rural area, roads go up and down, round corners but i dont drive like a total loon.

I think there is something wrong on the car, and ideas thoughts, anyone else had this issue ??

Paul




The control modules able to request activation by ERR (electrica reversible retractor) are SRS, SODL/SODR, RML/RMR and ASDM.
The seatbelt will be tensioned for up to approx. 10 seconds.

SRS

· Can occur during road run-off, according to criteria for CWS (Complex World Safety). The SRS control module makes a risk assessment and thereby determines the estimated degree of severity of the run-off situation. Based on this, the belt is tensioned with either 170 N or 300 N.

·

· SODL and SODR (option) May occur with the following criteria:

· Risk of rear-end collision according to the criteria for RCW (Rear Collision Warning).

Tensioning always occurs with high force, 300 N, if the car is stationary and with low force, 170 N, while driving.

RML and RMR May occur in the following scenarios:

· Panic braking, based on speed and requested braking torque from VDDM.

· Evasive action, based on current steering angle and angular velocity from SAS.

· Under/oversteer, based on the signals from IMU in the SRS control module and steering angle from SAS.

Tensioning always occurs with low force, 170 N.

ASDM

When the City Safety function requests full brake activation, ERR is also activated with 300 N tensioning force when the relative speed to the object exceeds approx. 20 km/h (approx. 12 mph).

Deactivation, unreeling of belt
Deactivation and unreeling of the belt occurs:
When the control module that requested activation shifts the signal from activation to deactivation. For deactivation to occur, the average retardation calculated by the acceleration sensors in the SRS control module must have decreased to 2.5 m/s (0.25 g) for 1 second.
When the pyrotechnic seatbelt tensioner is activated. In situations where the pyrotechnic seatbelt tensioner is activated, the electric motor for ERR is controlled in the opposite direction. This is to release the coupling from the transmission. This prevents the power spikes that would otherwise occur if the pyrotechnic tensioner also needed to actuate the transmission and electric motor on deployment.

Characteristics:
On deactivation and unreeling of the belt, a buzzing sound may be heard. This is completely normal.

ERR has a limited service life. After 50 activations with high force or 1000 activations with low force, the belt unit must be replaced. The driver will be informed of this by a message in DIM when the total number of permitted activations has been exceeded.

Hopefully this explains the system and the possible triggers.

[Deman77]

The way I read it It should be mainly low force which is 1000 times life apart from city safety, but there it says full breaking only - I think that more aggressive city safety activation than the usual false alarm ones. But then again there is no mention of mild city safety activation.
Can you ask for clarification if all city safety activations (whenever it flashes the icon) would result in full force pretensioning or just the ones that cause actual breaking.

If it’s all of them it’s really concerning as mine triggers at least a couple of times each weekend with false alarms but I remember only 2-3 timers when it actually breaked for me when I did things to uncomfortable for it. but I know that each activation does smth with breaks to prepare them.

[Paulj1]

The city safe one is where relative speed is greater than 20kmph

I can think of once where in queing trafic the car did the full on bollocks out stop......

in reality volvo are saying that ive had 85 full force applications in two years, i think id remember if i had !!!!

[Deman77]

I think city safety is inactive below that speed so that one is the red herring. I never got false ones on the bend with parked cars at sub 20mph The question to Volvo should be whether every city safety trigger results in high tension deployment. The correct answer should be no because otherwise all these false city safety triggers people get would blow seat belt units in a few months and this would be a top thread. The question is what kind of city safety tripping causes it. Is there a way to tell for the driver?

It sounds like one of your systems is hyperactive.

[Philip Fisher]

I get quite a lot of false alarms as do many others. On most occasions i get an alarm and the faintest pull of the belt which is over in a fraction of a second.

I have had a couple of occasions when I have had a full on stop on the motorway, the system alarms and the belt pulls nice and tight. This was usually my fault (ie not false alarm).

I had one occasion when the car saw a sign on a roundabout and activated full on auto stop with belts and all.

I have had plenty of p1551ng about on bumpy roads and humpback bridges when I have deliberately triggered the belts by way of demonstration.

If the motors have a very short life (which is what they are telling you) then I am a bit worried for the future.

[Philip Fisher]

Ok so thinking about this, I think the key question is what do the 35 represent?

Is it 35/1000 of part force deployments or 35/50 of full force deployments or a combination of both? If you can understand that from the dealer we might be part way to unravelling this.

Maybe all of us with 2 year old cars are racking up the deployments ready to hit the limit just out of warranty....

[Haldex]

Originally Posted by Deman77

..all these false city safety triggers people get would blow seat belt units in a few months and this would be a top thread.

I’m with Deman on this one.. in all my time on 5-6 different volvo forums this is the first time I’m hearing of this.. never read of anyone having to replace the belt tensioner unit over multiple false deployments..

[AB-UK]

Originally Posted by Philip Fisher

Is it 35/1000 of part force deployments or 35/50 of full force deployments or a combination of both? If you can understand that from the dealer we might be part way to unravelling this.

Maybe all of us with 2 year old cars are racking up the deployments ready to hit the limit just out of warranty....

Volvo Selekt should feature this number on any of their adverts for used cars, alongside the mileage since it's just as significant.

[Lexman8]

Originally Posted by Deman77

I think city safety is inactive below that speed so that one is the red herring. I never got false ones on the bend with parked cars at sub 20mph

On an XC90 (and probably other SPA cars), City Safety operates between 3 and 43 mph for MY16 and MY17 cars. On MY18 cars the upper limit is raised to 50 mph for pedestrians and cyclists. I don't know if earlier cars with updated s/w get the revised upper limit or whether it's h/w dependent.

For pedestrians and cyclists the relative speed has to be below 30 mph for intervention to occur. For stationary or slow-moving vehicles CS operates at up to 43 mph. Large animals are detected at up to 43 mph but braking is limited (by design) so you may still hit it. There are other limitations too: visibility, angle of approach, etc.

[BiggyG]

Originally Posted by AB-UK

Volvo Selekt should feature this number on any of their adverts for used cars, alongside the mileage since it's just as significant.

Yep, I recently discovered mine was an ex-rental. God knows how many times it was activated before!

I've had at least one full-force stop. Looked down as my wallet fell into footwell, and got the full stop treatment. The seatbelt really tightens and squeezes all the air out of you!