Hi all - I’ve for the most part wrapped up all projects on my 03 RX300, but then recently had the SRS warning light come on during a few hour drive with no obvious cause. I got techstream working and retrieved a B1100 code for the airbag sensor assembly. I thought I noticed an electrical smell but in hindsight that could have been just about anything.

I suspect this might be due to moisture. One of my projects was to stem a sunroof drain leak and then clean up the aftermath. The drivers side floor was saturated with water for an unknown length of time.

I stripped the interior yesterday and traced the extent of the water damage - it looks isolated to the footwell and clear of any wire harnesses. I ended up stripping and tossing a fair amount of ruined sub-carpet material. I found no mold and no visible corrosion here or anywhere else. Still, I can’t be 100% sure.

I checked all connections to the SRS module and seats, and am going to give them a spray with contact cleaner later today. However, I’m not especially hopefully because they appeared free of corrosion to my eye, and I kind of suspect more specific codes are thrown when a particular connection has failed.

I figure this ends with installation of a new sensor assembly, but I’m curious whether there’s any wisdom about this kind of thing here - possible routes of ingress for water I haven’t checked; likely failure points where it could have consequently shorted to ground. Long shot but figured I’d ask…

Thanks.

 

Try using a hair dryer to remove any remaining moisture from electrical connections.
Or put a rental carpet dryer fan in the car for a day or so. Others have done that to dry them.
Hopefully it will just dry and you can clear the code.

 

Try all the easy stuff first.

Do keep in mind that some of the SRS codes are considered 'sticky codes' [my term]. You need advanced code readers to clear these codes. My limited knowledge is that after certain duration the trigger becomes ineffective and one has to replace the bad bag [which one is yet another thing] and clear the code (else it gets set again).

I would highly encourage you to broaden your search outside Club Lexus [toyota] as this issue may be out of our league. [With apologies to the resident experts ... only because this issue has not been discussed frequently]. Once you do find out the steps/solution, please post back here so that we can enrich our learning.

Salim

 

Thanks both. As I suspected I didn’t have any luck cleaning the contacts. I reattached everything and still pulled the same B1100 code. (As far as clearing it - everything I’m reading says that SRS codes are scanned fresh with every startup - perhaps that is mistaken?)

I did make an unfortunate discovery. While removing panels from the passenger side to access the last mounting bolt for the airbag assembly, I realized that there is a lot of moisture over here as well, which I hadn’t anticipated. On this side it seems to be coming through the insulation which is waterlogged, but no standing water.

I have two theories - either the insulation wicked moisture from the drivers side to the passenger side over time, OR there is a secondary leak from the AC evap drain tube. In either case it could easily have gotten moisture into the SRS control unit under the gear shifter, as it is directly adjacent, leading to the control unit malfunction code. For that reason I think it’s the latter, because I replaced the compressor and was running the AC for the first extended period of time since purchase when the SRS light first came on.

I’m going to run the AC and check for moisture in the passenger footwell, and also feed some air through the drain. In the meantime going to order a new airbag sensor assembly. More to come…

 

Ok, problem solved. Here's a quick rundown of what I tried and what worked. Sorry that I don't have pictures - I was working on a busy street in Manhattan and wasn't thinking about photo documentation.

To recap: the problem was a steady SRS light on the dash, indicating the airbag system has thrown a fault and is disabled. Techstream gave me a B1100 code, indicating a malfunction with the center airbag sensor assembly.

TL;DR: moisture was a red herring. Replacement of old sensor assembly with new was painless and successful.

I want to mention first that in some prior posts this code has been interpreted as a nonspecific fault somewhere within the airbag system, requiring lots of diagnosis. From what I can tell this is not true. While on some Toyota vehicles there are roughly equivalent codes (B1000 for example) that indicate malfunction with the sensor assembly OR, for example, a short to ground somewhere else in the circuit, in the RX300 this fault ONLY means a sensor assembly malfunction. Had I known this I would not have spent so much time troubleshooting elsewhere.

First thing I did, as mentioned in my prior posts, was to disassemble the underside of the dashboard and the center stack below the shifter. My secondary motivation for doing this was to track the extent of the water intrusion into the cabin. Here is a rough and generally incomplete guide to disassembly. I winged it and found it very easy. There are probably many guides available that will walk through the process in more detail than I do here. But, roughly:
- First you will have to remove the scuff plates on the passenger and drivers side doors. These are loosely attached to the door seals with clips - you can essentially just muscle them off.
- From here on the drivers and passengers' side doors you can remove the trim panel closest to the scuff plate. I can't recall if there are mounting screws here, but if there are, they are obvbious.
- Drivers side: remove the panel beneath the steering wheel by removing the two mounting screws on the lower left and right corners.
- There are some connections to this panel that you will want to remove. The OBD connector can be unclipped by squeezing either side. The hood release is a bit more complicated - it is charged with a spring that you will probably need a small screwdriver to dismount.
- On the passenger side, unclip the panel above the passenger footwell. Then, open the glovebox and unscrew it where it is mounted at the corners.
- Finally, use a flathead screwdriver to pry up on the wood trim surrounding the center stack/gear selector. Remove all the screws attached to the adjacent interior panels. This will allow you to remove the center trim around the base of the center stack, inside the footwells. There are a few plastic clips remaining for you to detatch; they can be easily deactivated with a flathead screwdriver. The airbag sensor assembly lives inside of here.

With all the panels off, you can see ducting for the climate control running from the firewall to the dashboard vents, foot vents, rear vents, etc. On the other side of the base of the center stack, you will see two black ducts running from the floor to up to the center underside of the dash. To access the airbag center assembly you will have to remove these. They are not actually attached - just padded with foam to create a snug fit. If you push down and out on the duct you want to remove, it will come out. This is hard to explain but very intuitive once you see it. There is also a center duct that runs to the rear vents that in theory looks removable, but I have skinny arms and was able to work around it. YMMV.

As I removed panels, I discovered a pool of water in the drivers side footwell, saturating the insulation. I already knew there was some moisture here from the wetness of the carpet, but had fixed the leak and towel-dried the surface about a week prior, so I suspect this was more longstanding. I spent a few days drying the footwell as thoroughly as possible, and then continued disassembling.

Ok, with everything taken apart it's time to troubleshoot. First it is VERY IMPORTANT that you follow the service reccomendation of disconnecting the negative terminal from the battery AND wait a few minutes for all secondary power to discharge, as it has its own capacitive backup power to deploy the airbags even if power from the car is cut. This is because SRS is sensitive and may interpret tampering as an accident and deploy, which is extremely dangerous - not to mention counterproductive, since you are trying to service your airbag system. Don't skip this step.

With the battery disconnected and the airbag system discharged, the first thing I did was clean all the contacts I could access. SRS-related connections are easy to identify because they are yellow. I disconnected the three connectors to the center assembly as well as the connector under the drivers' seat and sprayed them with WD-40 contact cleaner on the male and female sides, followed by a light brushing with a cloth. I think this can be done more diligently, so I would advise reading about contact cleaning best practices, as well as try to locate the remaining, more inaccessible connectors. For me this was rather perfunctory as I had very low hopes it would work. Surprise, it did not.

Next I tried to track water ingress. My sunroof drains are both clogged, but the sunroof is broken, so I have the seals taped over (classy I know). I thought I was getting a leak at the A/C evap drain but it appeared to be passable ( ). In the cabin, I found a fair amount of moisture saturating the brown insulation tight to the firewall. A lot of this was really gross and I ended up ripping it out. It was wet EVERYWHERE, even in places that had no obvious route of ingress, so my best guess is that water from the drivers side or passenger side wicked through and saturated the rest. I wasn't able to reproduce the condition myself but will be keeping an eye on it.

In any case, once I had stripped the interior down to the sensor assembly, I became confident that the malfunction wasn't caused by moisture. The sensor assembly is attached to a mounting plate that sits about a centimeter above the car frame, meaning any water would have drained beneath it. There is a clear plastic visor protecting the connections from any moisture condition I could imagine based on body panel seams, proximity to carpeting/insulation, etc. (That's by no means a definitive conclusion for all kinds of interior moisture, just the one I reached in my case.) I was able to confirm my suspicions once I removed the sensor assembly and opened it up to inspect the electronics inside: absolutely no evidence of corrosion or water damage, old or new.

At this point replacement of the sensor assembly is as easy as unplugging the old one and plugging in the new one. You will need a T30 bit to remove the three mounting bolts holding the unit in place. They are a bit stubborn. Again, make sure your battery is disconnected and the unit is discharged by the time you do this - the only stories I've heard of accidental airbag deployment during service occured when servicing the airbag ECU without disconnecting the battery. The vibration produced by unbolting the sensor assembly or jiggling things around could easily cause a deployment condition on some vehicles.

Unfortunately, the unit in my model (891700W080) is no longer manufactured. Maybe this has been known for a while; it was a surprise to me, I found recent posts linking new OEM sensor assemblies now listed as discontinued. I ended up finding a used one on eBay for about $100. I mention that because the service manual STRONGLY discourages use of a used sensor assembly, but I think it's no longer possible to obtain a new one. No surprise there as these are all now 20+ years old. Make sure you verify that the airbags have not deployed on the donor car, as this will leave a behind a permanent deployment code.

Here is a link to the service manual I used to troubleshoot the sensor assembly. You can also find full service manuals for the RX300 by googling variations of "RX300 diagnostics pdf".

At this stage I called my mechanic, as I had seen evidence on the forums that a new sensor assembly might have to be paired with the car in ways I worried my - er - perfectly legitimate copy of Techstream wouldn't be capable of. He reassured me that any sensor assembly with an exactly matching part number would be plug and play, and the malfunction code would clear as soon as an operable unit were detected. Sure enough: I installed the replacement sensor assembly and the code disappeared, no clearing or pairing required.

As it turns out, failure of this sensor assembly isn't unheard of. It operates with very strict internal resistance and if this isn’t detected, a fault is thrown. I suspect that's what happened here, and the adjacent water intrusion was just a coincidence.

Sorry for the length - I found a dearth of info about this issue and wanted to be as thorough as possible. Please don't hesitate to get in touch if any of this is unclear. I will try to help talk you through it.

 

Thank you for enriching CL.

Salim