Abs speed sensors in the hubs provide the abs unit and ecu with the relative info for the speedometer to operate. Given the fault occurs at the same time, the circuit from the sensor isn't making contact.
Given that the sensors take the brunt of the grime and dirt from the road in between the hub and drive shaft it's more likely to fail before anything else on the circuit. It is showing an abs fault due to the discrepancy between the other sensors that are sending a signal.
Although it may be the abs unit, which is not impossible to fail.
The fact the brake fault and speedo occur after a while means it isn't a break in the communication or circuit but more of a voltage threshold issue, it was working ok before after all...
So now we have a puzzle...
To error on the side of caution, get the alternator charge state and voltage regulation checked properly at a tyre and exhaust center, its a free check
On tick over it should be 13.8 to 14.5v.
However while typing this one other outside possibility has sprung to mind....
The fault occurs when the car has warmed up yes?
When was the auxiliary belt last changed?
Maybe when the OP has checked the voltage it has been from cold start, with a warmed up engine the belt is stretching and thus a a drop In voltage...
A belt doesn't necessarily have to squeal when loose, especially when the ribs have lots of splits in between... Worth checking... It might be just that simple
As a layman so-to-speak with no full knowledge of the wiring, electronics etc I wish I could follow this with more experience as it seems like this is the kind of reply that might serve my issue well.
I would like to say that I find it hard to see this as a sensor problem! With the speedo averaging information from all sensors for its output, as it works initially every morning, I would have thought all sensors must be working?
I dont understand why a sensor would fail at the same time during the first journey of the day every day. It makes no sense to me.......?
With regard the drop in voltage..........
To me that makes the most sense but I had assumed it was likely a fault of the battery.
As stated I have checked the output of the battery at all times and since I started this thread, numerous times more.
The battery does need a charge as it sits idle at 12.4V when having not operated for 24 hours. I want to charge to a 12.6V reading after 24 hours of non-operation and is my next step. However, I expect this to make absolutely no difference as the issue started just after a service during which a new battery was installed. Re-charging it therefore is not likely to have any positive effect?
After running the car around for 5-10 minutes the batterys charge is at 12.8 reducing to 12.6 over approximately half an hour. It remains at that charge before dropping over a 24 hour period of non-operation to 12.4V as just stated.
The alternator puts out 13.8 - 14.0V so although not on the higher side of things as we stand today, for a 14 year old car I would say this is normal?
Therefore, these readings (with a charge of the battery) appear to suggest the battery and alternator are working (on their own) OK.
So how else would we see a drop in voltage potentially were that the issue here ?
I have not considered the auxiliary belt to this point and other than a recent service at 140,000 kms (Now at 142,400 approx.) I wouldn’t know when this was last checked or changed. Would it be checked on a service?
Also, Is it something I can look at and expect to see something obvious were there a problem?
Funnily enough this whine you speak of?
When I turn my engine off there is always a little whine, barely audible, for about three seconds, which I have noticed more recently. It sounds to me like something slowing down or some pressure being released, along those lines anyway. Its nothing major, just a slight whine for a few short seconds. It is, however, the last thing to be heard before the car falls silent?
That being said, while I have noticed it, that is only because I have spent a lot of time turning the engine off and on recently troubleshooting. It is not something I would consider out of the ordinary and is certainly not something that sounds WRONG
necassarily either. Rather, I am quite sure it has always been there though this could be an innacurate memory/assumption. I am not convinced, put it that way.
What do you think?
(P.S. I have a replacement ABS module on route from the UK. When that is fitted we should know whether the ABS unit is indeed the issue. For the record, I was loathe to order the unit I really was. Owing to the pattern of the problem, it seems to indicate that thee ABS module does work, if only for a little while each day, but work it does all the same. As such I am very grateful for your suggestions here and any follow up as I remain convinced that changing the ABS Unit will not fix the problem. Obviously, it will be great if I am wrong.)