Edition 46
Technical Trends
by Bryant Underwood, Public Safety Sourcing, Cassidian Communications

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We often bemoan the issues and complexities of Reverse Logistics (RL) with regard to computing or communications. However, one of the largest, interesting and most compelling aspects of RL is automotive service. For most of us, the way automotive service is delivered is a mystery when it’s good and a nightmare the rest of the time. Let me pull the curtain back and expose a little of the technical complexity in delivering automotive service with a real world example.

Recently a friend asked for help with a domestic SUV that had a very strange problem. The problem started when the cruise control became very intermittent. Sometimes when the owner attempted to turn the cruise control on or to set the speed they might have to press the button several times to get the cruise to set. The problem became progressively worse and then the cruise control just completely stopped working. Just before the cruise control stopped working the airbag warning light came on. So now we had two symptoms, the switches on the steering wheel for the cruise control and the airbag both reported errors. The trouble codes indicated the ignition switch was bad. I pulled the switch to check it to make sure before replacement. This in itself was no easy task because the switch is not really just a switch. It has a series of internal voltage dividers. These allow the vehicle control systems to detect multiple switch positions with less wiring and lower costs.

So to perform the test, I needed to validate the switch continuity and the various resistor values. The switch was fine and the resistors were all dead-on correct.


The next item in the troubleshooting tree is a little item called a ‘clockspring’. This is a pricey assembly of coiled cable that connects the airbag with the steering wheel controls. Since the airbag and cruise control were on the same circuit this looked like a bingo. Testing a clockspring can vary greatly. On this vehicle the assembly also housed the steering angle sensor for the traction control and anti-lock brake systems. With this configuration the testing would be almost impossible outside of an engineering lab. A replacement was the next logical step. The best price I could find for a new clockspring with shipping was for ~$650 for the entire assembly. I purchased one, changed it out. After getting the dash all back together I turned the key and started it up. In just a moment all hope left the building. I was greeted with the exact same warning lights and error codes as before. Did I mention you cannot return electronic parts for credit? I went back to the documentation. The only other part that could be causing the problem was the switch. At $50 it looked cheap. So even though my testing said all was fine, I picked one up and replaced it. Again, the same errors and warning lights flashed their insult at me from the instrument console. At this point I am ready to ‘get medieval’ on this problem.

What happened? Well I did get it fixed. After considerable troubleshooting and research I traced the problem to a spare 10A fuse. Notice I did not say blown fuse, I said spare. Turns out the owner towed a trailer that blew the fuse for the rear lights weeks before these problems cropped up. At the time the owner opened up the fuse holder and replaced the blown fuse from one in the ‘spare’ slot. All was good for a month or so with no issues. Then the gremlins started to appear.

Here is what happened. Almost all modern vehicles have an under-hood power distribution system packaged into what looks like a fuse holder. These typically are referred to with phrases like ‘Integrated Power Module’. A look inside reveals this is not a simple fuse holder but a very complex power distribution system.

So what was the problem? It turns out that most of these integrated power modules are made by one contract manufacturer as an ODM supporting several domestic auto manufacturers. To save costs, the ODM uses the same design with differing packaging and software depending on what vehicle or manufacturer the module is used on. On the vehicle I was troubleshooting the fuses that were labeled spare, would be used when the module was installed in another vehicle with differing software loads.


Since these particular fuses were not used on this car, someone decided to give them the “spare” label and just remove software references to them from the module. Clearly they are not spare and all the software was not corrected. There is some piece of rouge code that did not get modified properly for this SUV. Once the fuse was gone these obscure events eventually kicked off a software routine and the module started reporting errors. These errors were not mapped properly because at the root cause level they were errors for another vehicle, not this one. Since this is such an odd set of circumstances it most likely took years for this problem to bubble up for the manufacturer to see in the warranty repair data. Also, let me add there are no technical advisories that describe or address this problem in any way for the factory technicians. The factory techs I spoke with about this error were aware of the power module problems but had no idea about how crazy the problem was or how cheap the solution could be. These factory-trained techs performed the same troubleshooting I did. Except the next step for the factory-trained technician would be to replace the entire module for $700 followed by the wiring harness for $3000. This explains why I feel at least slightly satisfied to have gotten away with just $700 spent.

Why no technical bulletin? My guess is that this problem was known and understood by the factory and that the actuaries that did the math decided when all risks were considered it was not worth it. Sometimes there is a benefit to being silent.
RLM
Bryant Underwood manages Public Safety Sourcing for Cassidian Communications, an EADS North America Company in Frisco Texas.

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