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Discussion Starter · #1 ·
Last week I received the dreaded CHASSIS SETTINGS SERVICE REQUIRED.
VIDA showed a low voltage on the RR position sensor, so I replaced that tonight. That one is fine now (at least I think). But after a test drive, I got the message again. VIDA showed left rear acceleration sensor signal missing.
I looked in the rear at the sensor and wiggled the wires a bit. VIDA showed a good signal (roughly matching the other sensors voltages). A rescan for codes turned up nothing. I didn't re-drive it yet, but will in the AM.
Since there are now two sensors that all of the sudden are causing SUM codes, what is the likelihood that the SUM module itself is on the fritz?
The one code was a SUM-0081 which can be related to any of the accelerometers or position sensors.

Hoping someone has some insight because I don't want to keep replacing sensors if that's not going to solve the problem. 153k wonderful miles so far, but I'm expecting this stuff to start failing.
 

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Have you ever replaced your heater core? I got some weird messages and 4C button lights when mine went a few months back. Turns out that when the heater core fails, it leaks right on to the SUM module, which is by your right knee in the driver side foot well. Became apparent that was the issue when I noticed my driver-side carpet was a little damp.

I was able to revive my SUM module by removing it, scrubbing away residue on the PCB and components with a toothbrush and WD-40, and then letting it dry for a few days. Been solid since. Car is still driveable with the SUM removed, by the way.
 

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Discussion Starter · #4 ·
Some developments this AM.

SUM-0081 came back on, so I fired up VIDA and turned on the datalogging for the 3 accelerometers and 2 position sensors. I would get these random "flat spots" which I am guessing are NOT normal. On the second graph, where the arrow is, is when the CHASSIS SETTINGS SERVICE REQUIRED message appeared. It appears to get more rough after that and I believe that is because the suspension actually gets stiffer at that point. (Somewhere between SPORT and ADVANCED).

Those flat spots are random and I would guess there are several per minute that occur. The SUM-0081 is the only code I am currently getting now, and seeing that all my sensors are getting the same flat spot, I would guess its a power supply issue. I'd love to swap the SUM and see if the problem disappears.
Any chance someone has a SUM laying around that I could test?


 

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If SUM isn't programmed to a car, you're welcome to try one out of my totaled wagon. I'm 45 minutes away from you.
 

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I'm not sure if you've seen the other posts on the subject, but some people have discovered that there are several sensor power circuits on the R.

If these get shorted they will zero out the sensor values from the sensor set on that circuit. For that reason if the sum is still talking to the computer but several sensors are dropping out I'd start inspecting all the wiring on that particular circuit for wire loom damage and shorts.
 

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After looking at the values more intently, you are dropping values from both the front and rear sensors, so nix my thought that it may be a wiring issue. Might be good to check the SUM to see if its damaged or corroded.
 

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Discussion Starter · #8 · (Edited)
SUM is not programmed to car. I'd love to try this. I may be going through that way this weekend. Can you PM me your number?

Correction, it is programmed to car and requires VIDA subscription to download new software. Ugh.
 

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Discussion Starter · #9 ·
Bought a USB oscilloscope for further testing.
Wiring diagram shows that of the 7 accelerometer/position sensors, 6 of them come off of one SUM power circuit, and 1 is on its own. Strange, but we'll see what turns up.

I think I noticed something today, though. When I take a left turn, at speed, it causes it to trigger the code.
 

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Bought a USB oscilloscope for further testing.
Wiring diagram shows that of the 7 accelerometer/position sensors, 6 of them come off of one SUM power circuit, and 1 is on its own. Strange, but we'll see what turns up.

I think I noticed something today, though. When I take a left turn, at speed, it causes it to trigger the code.
That's probably the unit located in the trunk. It's the only asymmetric sensor in that there isn't a second one mounted in the same place on the other side of the car as is the case with the other 6.
 

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Discussion Starter · #11 ·
Actually its the left rear position sensor that is by itself. (the one that connects to the control arm)

So I connected the scope to the other power supply (that powers 6 sensors) and started driving. Took a left turn putting pressure on the right side and sure enough...CHASSIS message appeared and I was watching the voltage waveform bounce all over the place, instead of staying a steady 5vdc. So I knew something on that circuit did it.

Put it up on the lift and went with my gut. Took the right front wheel off and found the sensor wires worn through in 2 spots. It's been rubbing on the axle. This is precisely why I hate when other people touch my car. I was too busy when I needed to replace these shocks, so I had a reputable local indy shop do the job, but even they screwed up. They never secured the wires properly.

 

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Actually its the left rear position sensor that is by itself. (the one that connects to the control arm)
That's interesting. I wonder what the design motivation was for that.

As far as having other people work on your car, I can relate. A few months after having my struts replaced, I started getting the active chassis failure indicator. When we got underneath the car, we found that the strut cable had been severed. The installer did nothing to secure the cabling when he did the work. Thankfully the strut was replaced under warranty.
 

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At least you got it figured out and it's an easy fix :) Are you going to repair the wires or just replace the sensor/wire?
 

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Discussion Starter · #14 ·
At least you got it figured out and it's an easy fix :) Are you going to repair the wires or just replace the sensor/wire?
I had my wife take my car to the gym to confirm that the message doesn't reappear, but I'm fairly confident after seeing that mess.
Eventually I will replace that section of wire and probably remove some of it because it seems unnecessarily long. For now I just taped each wire individually and wrapped the whole thing, and zip tied it to one of the supports.
 

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I would get these random "flat spots" which I am guessing are NOT normal.

Sadly, those "flat spots" are 'normal' (or at least common). For all of 4C's deficiencies, that's not one of them. I'm not even sure it's a VIDA deficiency. IMHO it probably has more to do with the fact that windoze is not a real-time OS...

Good sleuthing on the wiring issue (most of the time, that's all it is...), and enjoy your new dso.

These SUMS are darn near bulletproof but, as some owneRs have learned, they are not very waterproof. In fact, that's why xemodex doesn't 'do' SUMs: the only ones they've seen are water-damaged beyond repair. (I wonder if the roughly-1-inch rubber grommets near the front that like to fall out of the underside of the floor pan can let water in?) Periodic checking for (grommet presence and) carpet dampness by one's right ankle is good advice for owneRs...
 

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Glad you found it. If you want a job done right, its always best to do it yourself if you have the skills and time, lol. I've lost track of all the little things I've fixed that other shops screwed up . . .
 
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