TCS C1225, Left Front excessive wheel speed var...

[TDK]

Folks,

We woke up to a few inches of snow at about 31F in Salt Lake City and drove through it for about 30-minutes. We then parked for about an hour and got some gas before the next 3-4 hour jaunt to Grand Junction. At the gas pump I noticed there was a speed bump just an inch or two ahead of the front tires. Upon leavning, the tires spun in some soft slush for a moment and the ABS kicked on, followed by "Service Stability System. I braked a bit, backed up for more room to get over the hump, but the message did not go away. I stopped, restarted and it was cleared from the display and my short-term as well.

There was no more buzzing or Stability messages for the next 600-miles or so, which included a lot of snow/ice at speed and dry runs up into the triples at times.

A couple days later in Denver at a clear-dry intersection with a moderate-start, it sounded like the ABS/stability kicked in at the left-front but no messages. I feathered the throttle for the next few starts and there were no problems. However, I got another ABS-buzzing later on a easy-clean start, (still no messages) so I checked codes. I found the C1225-history and cleared it to see it it re-occurs.

It also had the gas cap code history P0440 (emissions system, which did not re-occur after I simply tightened it.

There was a P0603 (long term memory reset) probably from when my son replaced the battery for us a few months ago when it was parked at his house for a while.

It seems odd that one wheel spin at relatively low speed/rpm would cause any significant damage to either a connection or sensor. Is it possible that there is a low-speed calibration value or whatever - that became corrupted by the immediate stop and restart?

I know that one of the first things is to check the speed-sensor electrical connection at the left-front wheel area. However, if it is out of reach, then I will have to take it to an oil-change type shop to have them check it. We are about 900-miles from the dealership we would normally take it to for this kind of minor thing.

I can only hope that does not screw up on the trip back, because we will have ample oppertunity to use the ABS/stability on the road at speed over the mountains west of Denver. And then there is the possibility of the infamous "speed limited to 90", which is kinda like a penalty flag.

This '99 is a fine car and has an identicaly-rated power-train. But both she and I think our '94 Concours (limited to 130, instead of 112), had more power. On these trips - the top end really was used too, (even though I got lectured every time).

Later,

[Cadillac Jim]

Sounds like you might have low air pressure in the left front. That is the first tire to pick up a nail from a shattered pallet falling off a truck on the freeway. Check the air pressure on all four tires. When the car is cold, set their pressure according to the information on the sticker on the driver's door pillar. If you're pulling off the highway with the tires warmed up, add two or three psi or set them all to the highest pressure you see in any of the four tires, whichever is higher.

[TDK]

Jim,

Thanks for the suggestion to check the air pressures, but unfortunately, all the tires are at 30#.

Note, when the buzzing first occurred, I was immediately concerned that the tranny had slipped or something. I do not believe that has happened nor have there been any tranny codes (which I assume would show up upon an actual malfunction).

I got the buzzing sound again today again on a moderate start, which I believe is the ABS/tstability getting a bit excited. I am a bit concerned that there is never any "traction active" message, which I assume should be showing up if indeed the traction control fires up. Then again, if it is a bit screwed up in its head, then all bets are off.

I disabled the traction via the glove-box switch and it appears to start in second but without any buzzing, even on a heavy-foot start.

The codes have not re-appeared (in particular the C1225 left front excessive wheel speed variation).

Yesterday afternoon, I had to have some emergency dental work on an absesced, root-canal. Therefore, I have not been able to get underneath to check the connection - which might be the most simple explanation.

Thanks for any other ideas or experiance in this regard.

[TDK]

Folks,

I put the left-front wheel up on the curb and fiddled with what I believe is the speed sensor cable, (it seemed to be looped above the brake line). There did not seem to be anything loose by tugging. I tried to seat the cable into whatever harness or socket (kinda tough without actually seeing it very well). There is one portion near the top by the fender liner that seems soft and flimsy by comparison, so perhaps the cable covering is missing or out of place there. It is also possible that cycling the traction control via the glove-box switch may have rattled its brains to where it reset properly.

In any case, I tried some heavy-foot starts and there was no indication of ABS/stability activating.

There wasnot good oppertunity to test the stability at speed on the trip from Denver to Grand Junction. However, we may run into some snow and ice on the remaing 640-miles, through Salt Lake City, so it is still on my mind.

If it continues to act-up, this will be a job for the dealership up on a proper lift - along with a few other minor items like a very intermittant-to-work trunk release (from either key fob or inside button) and to check the brakes.

Thanks again,

[TDK]

OK then,

I was considering some the front brake pads (or lack thereof) as being possibly related to the "service stability issue". I had to use the brakes hard and quick once, just after the mountain at some bumber-to-bumper traffic about 30-miles before Denver. It seemed then - that there was not a lot of pedal left and ther may have been some grinding noise as well later on. So perhaps the front brakes and specifically the left-front are not working up to par and creating the "service stability" code. Please let me know what you think about the following possibilities:

1. The brake fluid needs to be topped and bled (although being low should probably code as well). Regardless, there may be a bubble in the left-front causing improper actuation.

2. The left-front brake pad/rotor is much more worn, compared to the right-front.

In either case, the system itself might not be able to directly-measure the final control element (the hyd fluid bubble or lack of pad/rotor thickness), but only report an end result - with multiple possible causes.

Consider this: During the initial spin and stop, (which triggered a code of excessive left-front speed) - only the right-front actually stopped in time but the left-front spun longer because the ABS/stability could not get it to stop in time. Hence the computer threw out the excessive-variation code flag on the left-front.

The above proposition might not explanin the apparent ABS/stability application at some hard starts later on dry pavement. But maybe the tire actually spun or the ABS/stability computer has the line pressure/pulses to the left-front wheel cyclinder all jacked-up already - to compensate for the earlier, initial malfunction. It thinks the left-front brake need extra power - so it gets a little crazy on a hard take-off and actuates for a split second. Perhaps the left-front brake pad is stuck a bit (not enough silicone on the release pin problem noted elsewhere) and there is some lock-up resistance that has to be broken with a bit of power - resulting in noise akin to the ABS/stability.

The above is all conjecture on my part, but I would appreciate any input on the topic and specifically - on how the Stability works in a '99 DeVille base.

We made it back fine and I'll be making an appointment with the GM dealer, who has done nice work for me int he past.

BTW:

The BWD (Big White Dog) averaged 23.6 mpg and 74.6 mph on the trip home from Denver of 950-miles, (including 2-gas stops, 2-other-than-driver potty stops and a detour to lunch/shopping in Salt Lake City.

Thanks all,