DECIPHERING CODES

[voicepro]

I've been getting a SVC STABILITY SYS display on the dash cluster, but even after referring to my Owners' Maual and running all the

codes, I can't figure out just what needs to be serviced or repaired. The code is TCS C1228. Anyone know what the heck I'm supposed

to do about this one? Appreciate the input. Hit me at voicepro@att.net please. Many thanks. Oh...1998 DeVille DeElegance.

[Cadillac Jim]

C1228 Right Rear Excessive Wheel Speed Variation

First, check for proper tire pressure. Second, if you can jack up the wheel, see if it is out-of-round; if it is, likely there is a tire bruise (damaged cord) and there is possible danger of a blowout. If those are good, have the wheels balanced.

[voicepro]

Thanks very much, Jim. I've been in touch with my shop and they want me to come in tomorrow so they can look into replacing the struts...which likely is the problem. Tires are almost new -- less than five grand on them -- and

I check inflation pretty regularly. Have suspected for some time the suspension wasn't quite up to par, so perhaps my seat-of-the-pants sense was telling me something it took a few more miles for the on-board diagnoistics to

reveal. With no specific part indicated, I just wasn't sure what to look at...but my shop has some old-line guys, and I trust their analysis. Appreciate your input.

[cdgrinci]

Wouldn't a wheel speed sensor incite this type code; check for bad sensor, dirty sensor or loose wiring; just a guess on my part.

[Cadillac Jim]

Yes, an intermittent or scratchy connection can cause a C1228. It's intended to catch a wheel changing RPM too much as it bounces over a pothole or if it is badly out-of-balance or out-of-round and bounces on the pavement. This can happen with little sound or feel in the cabin when it is on the rear, particularly on the passenger side.

Poor damping can cause bouncing when the tire and wheel are just fine, but the damping has to be essentially zero to cause a good wheel to throw a C1228. If your car passes the "bounce test" (put your weight on one corner of the car, then release, if it comes back up more than once, it fails) but I've never seen OEM shocks or struts on any Cadillac ever get so bad that it fails the bounce test. Since the code is always on one wheel, I would look at the tires and wheels first.

A new tire can be out-of-round. In fact, most are, so some degree. A top-notch tire shop will use a special machine to skim a fraction of a millimeter off new mounted tires to bring the tires in to a perfect roundness. Then, other new tires can have an asymmetry in the cord that causes their rolling radius to vary as the tire rolls, an effective out-of-round condition that can be found only with a road force balance and requires that the tire be replaced.

[voicepro]

...not sure if I'm out of the woods yet. Per your suggestion, I went first to my tire store and had them pull all four, examine them

for damage, rebalance and rotate them. As an aside, they said most folks don't, but should have their balance checked every

year. In my case, the right front was showing a significant wobble, so they rebalanced it and it went to the right rear as part

of the rotation (which was due anyway at 10-12,000 miles on the tires).

...then I went to my garage and told my mechanic my issue, and suggested first I'd like to clear all the codes and start over.

He told me to disconnect the battery terminals, hold the ends (- and +) together for a couple minutes, then just let the car

sit for a half hour or so. I did this...the hooked the battery up again and headed for home.

...the ride home -- about twenty miles or so -- was uneventful, and about half that distance was at freeway speed. And so

far, not a single code is showing. I'll keep an eye on it for the next couple of days, of course, and get back to the garage

if it reappears, but it looks to me as if rebalancing the tires was the key to SVC STABILITY SYS...at least in my case.

...thanks for your input and wisdom, Jim.

[rockfangd]

interesting.

My eldo has a slightly bent wheel on the right front and it causes a little wobble but does not throw any codes or messages. Keep us posted

[voicepro]

...well, drat! Thought I had the problem solved. But the SVC STABILITY SYS message, along with the Traction Control and Anti-Lock Brake icons. One in a while

they're even accompanied by the Service Engine Soon light, but that's intermittent.

...I guess I'll have to let my garage have a look at the car after all.

...I did eyeball the brake pads when they were rotating the tires yesterday, and they looked fine.

...beats me what the C1228 code is trying to tell me. I wish I could put my finger on the specific component that wants repair or replacement.

...any ideas?

[Texas Jim]

C1228 - Right rear excessive wheel speed variation

Have you unplugged the sensor on that wheel and plugged it back in two or three times??

If not, that would be the first thing I would try... It may just be dirty or maybe not plugged in good.

If that don't help, you probably need to replace the wheel sensor.

On some model years, the sensor can be replaced by itself... on some other model years, the sensor is built into the hub and the whole hub has to be replaced.

[voicepro]

...well, I'll be dipped. Something as simple as that, huh? Okay...I'll have a go at it, Jim...and thanks very much for sticking with me during this (relatively minor) ordeal.