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Thursday, February 29, 2024

Doug's Domain

Doug Vetter, ATP/CFI

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Saturday, February 16, 2013

Another SRS Fault Light

Last weekend I took my mother out to lunch. After we said our goodbyes and I hopped in the car to head home I noticed the glaring red airbag warning light illuminated. "No fair" I said aloud in my best Bart Simpson voice, "Not my fault...I didn't do it". My internal troubleshooting subroutine whirred and clanked a few moments. When the rusty gears ground to a halt and the bell went "ding", I came up with two possibilities: one of the airbags had finally given up the ghost and failed a Power-On Self Test (POST), or one of the system sensors had failed.

A few days later, coincidentally 15 years to the day I picked up the car at this dealership in 1998, I drove the car into my tech's bay. We connected the latest factory diagnostic system (SSS), this time via what appeared to be a new wireless head. Given the long history of problems with the new system talking to this old car I was somewhat skeptical that it would work but sure enough it did. We read the fault memory and the result was almost predictable: one occurrence of an open circuit in the passenger side occupancy mat.

(Image: Screenshot of the SSS showing the fault memory scan)My technician explained that the mat is constructed of an electrical lattice of sorts that conducts when someone sits in the seat. The mat is connected to a sensor that interprets the signals coming from the mat, and passes a signal to the SRS module to indicate whether the seat is occupied. This is simple compared to the currently-shipping systems that basically take an electrical image of whatever is present in the seat, whether it be one's posterior or a child seat, and not only determine whether to fire the airbag in a collision (as is the case in the E36) but also to alter the strength and timing with which the airbag is fired, the purpose being to reduce the chance for injuries.

That brings me to point out that while it's normally very important to know how to adjust the seat for the proper driving position for comfort and visibility, it's particularly important in older vehicles like the E36 because its airbags are dumb and dutiful -- assuming the occupancy sensor says "go boom" – they will fire at a predefined time and expand at a predefined rate. This timing assumes the occupant is a specific distance away from the airbag. If you sit too close or too far away from the airbag it can cause serious injuries. The worst case scenario is that your face meets the airbag precisely as the bag reaches full expansion. This has been known to break facial bones. Think about that next time you're driving down the road with the seat reclined back and your hand draped on top of the wheel trying to look cool.

My technician knowingly raised the passenger seat to verify the connector on the sensor mounted to the bottom of the seat was fastened and found that in good shape. He then suggested that we clear the fault memory to see if that takes care of it and then replace the mat and sensor as an assembly only if the problem returns. The issue, of course, is that while the sensor can be replaced relatively easily, the mat requires lifting the seat foam base, four new "tree" fasteners, etc. and both procedures involve removal of the seat from the vehicle – something I would obviously prefer to delay until the upcoming leather installation. Only time will tell if I get my wish.

Windshield Washer Fluid Reformulated

BMW appears to have reformulated (and not in a good way, IMHO) their windshield washer fluid concentrate. I've used this stuff for years because it has always been reasonably priced (in part because I'm not paying to ship water as I would in the case of pre-mixed stuff), I can dilute it accordingly depending on the time of year, and it's always performed well.

Looking at the labels of the old and new fluids, the original fluid contains:

...while the new fluid apparently only contains Methyl Alcohol and “bittering agents” to dissuade the intellectually challenged and substance dependent from consuming it. The fluid is now tinted blue and has basically no smell, at least as compared to the original stuff. It also appears to have a thinner viscosity. I bought four bottles of the stuff before I knew it had been reformulated and I still have several bottles of the old stuff so I plan to do some A-B comparisons and report my findings. If I find the new stuff sucks I'll start mixing my own.

Wiper Refills Changed

I visited the parts counter looking for wiper blade refills and confirmed a rumor provided by a colleague that BMW has changed the wiper blade refill kits to exclude the metal splines. The splines tend to hold up well (meaning they don't rust) so ordinarily I'd just chalk this up to typical BMW nickel and diming and go about my day. Except that the new rubber blades don't seem to mate properly with the splines due to a problem with the way they are molded...perhaps because they have to work for several applications. I replaced a set on a friend's E39 recently and found I had to cut out a small ridge of rubber from the sides of one end of the blade so it would mate properly with his original splines.

The alternative, naturally, is to buy new blade holders which come with new blades already installed. The assemblies vary in price by model but are generally $100 for the set. I'll try to use the new refills on the E36, but if I'm not happy I'll go looking for an aftermarket (perhaps Bosch-branded) solution and give the middle finger to BMW yet again. Why can't they just leave well enough alone?

Mileage: 232044, Parts: $15