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[TheBoy]

Never really thought of this, until she started moaning about it, and she's right...

V6 servotronic, uses speed signal to reduce assistance as you get faster.

So why is it, when speed signal disappears, due to intermittent ABS ECU, does the steering go heavy? Surely it should be as light as anything, as it assumes you're not moving, thus need maximum assistance?

[Entwood]

Never really thought of this, until she started moaning about it, and she's right...

V6 servotronic, uses speed signal to reduce assistance as you get faster.

So why is it, when speed signal disappears, due to intermittent ABS ECU, does the steering go heavy? Surely it should be as light as anything, as it assumes you're not moving, thus need maximum assistance?

Opposite I thought.. goes to mimimum assistance as it "assumes" you may be do some much faster speeds and too much assistance would be dangerous .. so in the name of safety, no signal = no assistance

[Andy B]

Never really thought of this, until she started moaning about it, and she's right...

V6 servotronic, uses speed signal to reduce assistance as you get faster.

So why is it, when speed signal disappears, due to intermittent ABS ECU, does the steering go heavy? Surely it should be as light as anything, as it assumes you're not moving, thus need maximum assistance?

Opposite I thought.. goes to mimimum assistance as it "assumes" you may be do some much faster speeds and too much assistance would be dangerous .. so in the name of safety, no signal = no assistance

Sounds a reasonable assumption to me     

I remember taking my 2.2 Carlton onto the motorway for the first time, I'd never had power steering before, & this was the usual basic always on type of assistance. It felt like I only needed to look hard at the wheel & it'd move! 

[Kevin Wood]

Yes, I'd guess it "fails safe" to minimum assistance by design too.

[TheBoy]

I understand the failsafe argument, but how does the servotronic ECU know. AFAIK, it only receives speed signal, nought else. So it will just assume standstill?

[TheBoy]

Can you tell I was laying awke last night, pondering this one

[aaronjb]

I understand the failsafe argument, but how does the servotronic ECU know. AFAIK, it only receives speed signal, nought else. So it will just assume standstill?

Does it receive RPM by any chance, as well? I know the Corsa electric PAS system does, for that reason..

[Kevin Wood]

IIRC, the steering goes heavy after the ABS ECU has actually failed while the vehicle is moving or if it wasn't there (or working) at startup. I guess the servotronic box looks for activity at startup of the ABS ECU, and invalid activity such as coming to an impossibly sudden halt from <mumble> MPH, and, if it sees this, goes into a fail-safe mode.

There's also the possibly that it it's simply that the signal is normally in one state when the car is stopped, but, with a failed ECU, it reverts to the opposite state.

The servotronic box raises a code if it detects a faulty speed signal input, so there must be some intelligence in it. Granted, it only has the speed signal as an input so it can't compare it to anything else to determine if the car is likely to be moving.

[TheBoy]

IIRC, the steering goes heavy after the ABS ECU has actually failed while the vehicle is moving or if it wasn't there (or working) at startup. I guess the servotronic box looks for activity at startup of the ABS ECU, and invalid activity such as coming to an impossibly sudden halt from <mumble> MPH, and, if it sees this, goes into a fail-safe mode.

That was my feeling. But, whilst pondering it, surely it wouldn't go to failsafe in a 100% brake locked up stop, as I bet they are the same config for ABS and non ABS models.

I'd check for servotronic codes, and see what configs it has on, if only I had the facilities 


Moving to car chat, as its not a help request (as we all know what the cure is), more of a discussion point

[Kevin Wood]

I'd check for servotronic codes, and see what configs it has on, if only I had the facilities 

I can bring the Tech 2 to Serek's on Sunday (if I make it). Alternatively, I'll be passing your way in a couple of weeks anyway.