We have just picked up a fairly clean, 27k mile, 2004 Corsa C 1.2 16V for a member of the family and because daughter drove her 01 Corsa for
10 years / 60K miles and to 200+ k miles, when she drove it home from the (backstreet) dealer she fairly quickly felt it had a subtle steering funny.
The Corsa C's have EPS (Electronic Power Steering) so basically the steering column is driven by an electric motor though a very simple steering rack. The amount of 'assist' is managed though the ECU's and is backed off as the road speed increases. All that seems to be working fine.
Along with ticking off all the basics (tyre pressures, tyre condition, 4 wheel laser alignment / tracking etc) and getting a couple of local garages to test drive it for us, we all seem to agree there is something, we aren't any closer to what might be the cause, even if we now know more about what isn't.
Because it's 'electric' I have also tested the battery / charging system and although bioth are 'Good', they might be considered 'a bit weak'. Eg, system voltage sits at 14.2V at engine idle, and when you apply any load (headlights, rear screen heater, blower, air-con or turn the steering wheel etc) you see on the OBD scope the voltage drop but unless the load is max, it recovers to 14.2 within a few seconds. At absolute max load it might drop to 13.9 and continue to fall slightly over time.
Comparing that to my Meriva of the same year, that sits at 14.4V under all load situations but that may well have a higher capacity alternator (that is also very new) and a higher capacity battery.
So, the steering symptoms are that as you are say exiting a large fast roundabout, the car will generally self centre but not quite all the way. Eg, it might continue slightly to the left ... it seems to have this 'sticky' spot around the middle? I feel it's only mild because the camber of the road also impacts the effect.
With the vehicle up in the air and with the engine running you can take the steering from lock to lock by hand using either road wheel.
When you are only moving slowly you are getting the most power steering assistance and the self centering isn't so apparent / expected it seems less noticeable as an issue. Eg, the EPS 'masks' the issue to some degree.
So, working on the basis that there is some excess friction in the steering system somewhere (not much else would limit caster induced self centering I don't think), the bits that could add friction are, top strut bearing, lower strut ball joint, drop link, track road end, inner track control arm joint, rack, steering column coupling and the column / motor drive assy.
I have ideas for tests to try to isolate some of that.
Lift the front and drop the track rod ends and steer the leg(s) manually and check for any tightness / binding.
Check the ease of movement of the track road end and track control arm inner joints.
Remove the steering coupling and check for binding.
I'm not sure yet what if anything could cause binding in the steering column itself or if there is anything that could be stripped, like to EPS motor etc.
Then it's down to the (very simple) steering rack that whilst looking easy to strip / clean / check / re-lube / re-assemble etc, looks like a bit of a PITA to get off (you have to drop the rear of the subframe & exhaust etc).
So this was really an overview of what we have felt / seen / done so far in the hope that someone might have seen similar on a similar system and so may be able to give us a good pointer to the most likely to be the cause.
We factored the thought that we may have to do / spend something on such things but that extra cost would be worth it for the final solution etc.
Part of that was familiarity with and fondness for the Corsa C as a simple and functional solution (and the Meriva A is built on the Corsa C platform and daughter and I have Meriva A's) and we also have some special tools and diagnostic kit etc.
And FWIW, even daughters 2001 Corsa was ULEZ compliant, as is this 2004 Corsa of course and both Merivas. ;-)
Cheers, T i m