Rollover Sensor Issue

[Polkat]

Hello all. Brand new to the forum. I've owned a 2005 2WD TB LS since 2006.

My Trailblazer has an airbag light on. The codes that came back were B3855 and B3856. I was able to find this in Google in reference to another GM vehicle:
DTC B3855

Rollover Sensor Performance

DTC B3856

Discard Rollover Sensor

and:

B3855:

A valid ID message is not received within 5 seconds of the ROS being powered up.
A status message is not received.

B3856:

The SDM has received a NOK message from the ROS.
A ROS internal fault exists for a 127 ignition cycles.

I'm guessing ROS = rollover sensor

I've removed all of the interior to get to the rollover sensor (behind center console in front of rear seats). Nothing looks physically wrong with the sensor and as far as I can tell, the connection looks good. The part number is 15250669.

My question is, how dangerous would it be for me to replace this myself? I can't find an exact part number match on any parts websites, but it looks like it will be around $300 for a new one, which seems ridiculous to me. I was able to find a used one on ebay for around $50.

My fear is if I replace this thing with the used ebay part, or a "new" one for that matter, will it be dangerous?

Has anyone had any experience with this?

Thanks!

 

[MAY03LT]

I've removed all of the interior to get to the rollover sensor (behind center console in front of rear seats). Nothing looks physically wrong with the sensor and as far as I can tell, the connection looks good. The part number is 15250669.

My question is, how dangerous would it be for me to replace this myself? I can't find an exact part number match on any parts websites, but it looks like it will be around $300 for a new one, which seems ridiculous to me. I was able to find a used one on ebay for around $50.

My fear is if I replace this thing with the used ebay part, or a "new" one for that matter, will it be dangerous?

Has anyone had any experience with this?

Welcome to the site!

The info that you posted matches our service info to a tee. There are no test procedures for testing the ROS itself, they want the 3 wires to the ROS to be tested if it's not a current (active) fault. However, they said the same thing about the 2 wire impact sensors, and those can be tested. If you've had the codes cleared, and the light immediately came back on, I think banging in a replacement sensor is a good first step.

Very few things make me uneasy about working on vehicles, but airbags are one of them. The service information does not mention if the battery needs to be disconnected, but in all of the test procedures, it only wants the key OFF when unplugging/plugging in the sensor. So I think you'll be ok if you don't disconnect the battery.

Removal Procedure

Fold back the rear carpet in order to gain access to the sensor. Refer to Carpet Replacement - Rear in Interior Trim.
Disconnect the electrical connector.
Remove the nuts securing the rollover sensor to the floor panel.

Installation Procedure

Install the nuts securing the rollover sensor to the floor panel.
Tighten the screws to 10 N·m (88 lb in).
Connect the electrical connectors.
Install the rear carpet. Refer to Carpet Replacement - Rear in Interior Trim.

 

[Polkat]

Thanks for the help.

A little more background: My TB has 97,000 miles on it and the transmission is toast (no second gear and first gear is on the way out too). My wife and I are trying to decide if this vehicle is worth trying to fix or not. Replacing the transmission will be expensive enough, but the deciding factor is if I can fix the airbag system. If I can fix the problem, we will dump $$$ into the tranny, if not, new vehicle time.


Before accessing the rollover sensor, I followed the airbag control module removal instructions for the 2004 TB via the posted service manual (I disconnected the connectors to all the sensors but I did not actually remove the control module). It appears the 2004 TB does not have a rollover sensor so I was confused at first when going through the service manual. I also pulled the airbag fuse under the hood and disconnected the neg battery cable to be safe.

My wife is afraid if I mess with the sensor, or replace it, the airbags will deploy as soon as I reconnect the sensors and power. We definitely don't want that to happen for obvious reasons...

Is it worth the risk (if there is any real risk at all)?

Thanks again!

 

[MAY03LT]

Thanks for the help. A little more background: My TB has 97,000 miles on it and the transmission is toast (no second gear and first gear is on the way out too). My wife and I are trying to decide if this vehicle is worth trying to fix or not. Replacing the transmission will be expensive enough, but the deciding factor is if I can fix the airbag system. If I can fix the problem, we will dump $$$ into the tranny, if not, new vehicle time.

Man, that's a tough call. Even though everything points to the ROS, nothing is guaranteed. I'd hate to see it not be a $50 (used) sensor and then need further diagnosis or even the airbag module. Decisions, decisions....

Before accessing the rollover sensor, I followed the airbag control module removal instructions for the 2004 TB via the posted service manual (I disconnected the connectors to all the sensors but I did not actually remove the control module). It appears the 2004 TB does not have a rollover sensor so I was confused at first when going through the service manual. I also pulled the airbag fuse under the hood and disconnected the neg battery cable to be safe.

I did the same thing! I noticed they have 04 airbags in the 02-05 manual. I didn't check if the ROS was in the 06 manual, I went right to the OEM manual for 05.

I am anti-battery disconnecting, but any airbag work is the #1 exception. I witnessed a bad mishap when another technician made an error when doing a repair which involved moving an airbag module (battery hooked up). Ever since then, I am super cautious.

My wife is afraid if I mess with the sensor, or replace it, the airbags will deploy as soon as I reconnect the sensors and power. We definitely don't want that to happen for obvious reasons...

Is it worth the risk (if there is any real risk at all)?

Thanks again!

I think you'll be be fine. You seem to take safety seriously so I say go for it. I think the worst case scenario would be that the new (used) ROS has a fault and you'd be back at square one with the stupid light being on.

I don't have my notes in front of me, but the criteria for the airbags to go off is almost a novel. The ROS troubleshooting chart included each of it's circuits shorted, and all that did was turn on light/set codes.

Also, no prob man, and good luck with whichever route you go!

 

[Polkat]

Well, I figured I'd take a $50 chance and ordered the ebay ROS. If it doesn't work I will be out ~$50 and move on. I'll post my results after the part comes in.

 

[C-ya]

MAY (or roadie), I haven't looked in the book, but why is the ROS in the airbag circuit? Or is it even in that circuit? Maybe they light that light to make sure the right codes are scanned. The only experience I have with an ROS is in my fuel-injected street bike. It has an ROS in it to turn the fuel pump off in the event of an accident and the bike is laying on its side.

 

[bobdec]

From GM sales literature.. " Curtain side-impact airbags with a rollover sensing system designed to provide increased head protection are available on 2005 models." Addded in 2005 as a $425.00 option.

 

[C-ya]

From GM sales literature.. " Curtain side-impact airbags with a rollover sensing system designed to provide increased head protection are available on 2005 models." Addded in 2005 as a $425.00 option.

Good to know. One of the few options my truck doesn't have.

 

[wesman43]

From GM sales literature.. " Curtain side-impact airbags with a rollover sensing system designed to provide increased head protection are available on 2005 models." Addded in 2005 as a $425.00 option.

Ugh I would gladly pay that much. Wish mine had em.

 

[Polkat]

Well this sucks...

Removal Procedure

Fold back the rear carpet in order to gain access to the sensor. Refer to Carpet Replacement - Rear in Interior Trim.
Disconnect the electrical connector.
Remove the nuts securing the rollover sensor to the floor panel.

Installation Procedure

Install the nuts securing the rollover sensor to the floor panel.
Tighten the screws to 10 N·m (88 lb in).
Connect the electrical connectors.
Install the rear carpet. Refer to Carpet Replacement - Rear in Interior Trim.

I was trying to tighten the screws to 10 N·m (88 lb in) as directed in the instructions. That seemed really tight, but I figured it must be due to not wanting the ROS to work itself loose and two of the screws separated from the floor panel. It almost looks like they were glued to the floor. However they were connected to the floor panel, they weren't connected strongly enough to handle that much torque...

Now I am completely at a loss for what to do....JB Weld I guess?

 

[Polkat]

The good news is, the Ebay ROS worked and the airbag light is off!

The bad news is, I don't trust epoxy holding the ROS mounting bolts to the floor, even though that's what seemed to be holding them to the floor before.

I worry that someday someone is going to inadvertently kick the sensor (its right in front of the back seat) and jar it loose, possibly making the roof airbags deploy.

We were leaning towards selling this vehicle before the mounting bolts broke, but I can't do that in good conscience if that sensor isn't mounted properly. Anyone have any advice?

Thanks

 

[NJTB]

The good news is, the Ebay ROS worked and the airbag light is off!

The bad news is, I don't trust epoxy holding the ROS mounting bolts to the floor, even though that's what seemed to be holding them to the floor before.

I worry that someday someone is going to inadvertently kick the sensor (its right in front of the back seat) and jar it loose, possibly making the roof airbags deploy.

We were leaning towards selling this vehicle before the mounting bolts broke, but I can't do that in good conscience if that sensor isn't mounted properly. Anyone have any advice?

Thanks

Can you drill through the floor and put a nut and bolt on the sensor? I don't know what's on the other side of the floor, so be careful.