Service Stability System Message

[SwampeastMike]

Bought the car in winter, 2008 and had occasional "Service Stability System" message from the DIC. Found a leaking rear shock and replaced all shocks & struts with OEM. Message never appeared through the summer. Now with cooler weather, it has returned. Still infrequent, and always occurs ONCE per drive cycle (near the very beginning) with cold engine and ALWAYS when going around specific corners. These corners are at the bottom of hills where I'm heading down and turning up. One corner in particular has a very funky pitch. I sometimes hear a quite loud noise from the underside (seems to be slightly in front, left of the passenger seat) for a few seconds. The braking solenoids?

I don't have a Tech-II scan tool, but do have one from Auto Engenuity with enhanced GM. Have checked a couple of times (not in the drive cycle with the error) but find zero DTCs. Any idea what's up? I do know that my scan tool works fairly well for this car as I've identified a number of minor problems and made repair before they became major.

[SwampeastMike]

More info:

Message occurred again, checked fairly quickly and found some related DTCs in history:

C1286 (steering/lateral accelerometer sensor bias malfunction) and C1287 (steering sensor rate malfunction).

My scan tool isn't the best but was able to verify that the steering wheel position sensor was giving the correct values--at least in the garage with a nice warm car. Four wheel alignment recently performed after brakes, shocks & struts replaced. Shop said they couldn't get it "perfect" but it's the best alignment I've experienced in any car including brand new. 40 mph to 0 mph with hands off wheel.

Next step according to manual is to verify wiring and connections. Can certainly do, but given the number of modules involved and locations all over and what almost certainly seems to be an intermittent problem (and only when vehicle is physically cold--garage is unheated and parked in the weather during most days), would truly appreciate some advice of where to REALLY look. I'm suspecting the steering suspension sensor. Is this a common problem for a car of this age (99)?

[John Wicz]

Hi,

I don't have the C1286 but do have C1287 (history), mine just started giving me the message also. Pretty sure from all that I've read that it is the Steering Position Sensor.

[SwampeastMike]

Thanks. Believe I'll clean the position sensor connector nicely, check routing of wiring and wait. Expensive part that doesn't look particularly fun to replace. Other thing I've noticed/remembered is that the problem only happens in cool, humid weather. Not sure of the internal construction of the thing, but have a sneaking suspicion that it's supposed to be completely sealed and that a tiny air leak is allowing a condensation problem.

[John Wicz]

Thanks. Believe I'll clean the position sensor connector nicely, check routing of wiring and wait. Expensive part that doesn't look particularly fun to replace. Other thing I've noticed/remembered is that the problem only happens in cool, humid weather. Not sure of the internal construction of the thing, but have a sneaking suspicion that it's supposed to be completely sealed and that a tiny air leak is allowing a condensation problem.

I bought a new one, it is plastic. I don't think that cleaning the connector is going to help (although it can't hurt). It is a dealer stocked item if that tells you anything........

I paid $60 for the new sensor and will be able to report more on the difficulty after I attempt to replace mine in the next couple of days.

[SwampeastMike]

Thanks. Believe I'll clean the position sensor connector nicely, check routing of wiring and wait. Expensive part that doesn't look particularly fun to replace. Other thing I've noticed/remembered is that the problem only happens in cool, humid weather. Not sure of the internal construction of the thing, but have a sneaking suspicion that it's supposed to be completely sealed and that a tiny air leak is allowing a condensation problem.

I bought a new one, it is plastic. I don't think that cleaning the connector is going to help (although it can't hurt). It is a dealer stocked item if that tells you anything........

I paid $60 for the new sensor and will be able to report more on the difficulty after I attempt to replace mine in the next couple of days.

Yep, dealer stock definitely tells me something... Only part for mine I've found in stock is the coolant tank cap. Yes, please report on the difficulty. Since it's the first thing to come off the base of the steering column, it seems that the column can be removed with wheel and covers in place. Thought I read something in the manual about a re-calibration or something similar after replacing the position sensor requiring a Tech II tool, but can't seem to find it now. Is such requuired?

[John Wicz]

I changed my sensor this weekend, not too hard. The toughest part for me was the intermediate shaft and getting the boot back on the rack (I gave up on trying to disconnect it from the column end and found it much easier to disconnect it from the rack side) but, trying to get the boot back on the rack is a different story.

There is no re-cal necessary. You need to make sure that you have an "E7" external torx socket to hold the studs that the 6 column nuts attach to. Basically you disconnect the intermediate shaft, disconnect about a half dozen electrical connectors, remove the 6 (13mm) nuts and the column pulls out.

Once the column is out, completely remove the intermediate shaft, pull off the plastic cover, remove the sensor retainer then the sensor and then put the new sensor in, remove the sensor locating pin and then put everything back together.

Maybe someone knows an easy way to replace the boot back on the rack, but I spent a lot of time on this part (and I'm still not sure that it is totally down "tight" on the rack).