I have had an ongoing, intermittent ABS "thing". Is it so that our cars mainly need new CU's, or is it something cheaper to check first?

Since I bought my car ( a year ago) the ABS-light has lit up a few times.

First time at the dealer, the checked all the connectors (wich had water in them) and cleaned them. Second time, they were going to do some rewiring (a kit that was made for this car). The dealer found out that the previous owner already did that, so they left that. Instead, they were measuring around on the circuit, cleaning connectors etc.

They said that they did not know if this would fix it, since they really did not know the source of the problem.

I was told that if the problem continues, they would have to consult the Volvo importer for other known sources.

So far, this only cost me an hour of workshop bills, but I suspect that next visit will include starting to change parts.

-The symptomes are:

Before my first "fix", the light would light up now and then while braking somewhat hard under wet or dry conditions. Sometimes (or always) the ABS function would fail until next startup.

After my first visit, on a warm vacationtrip, the ABS light could come up when idling on a hot place (hot sun and engaged AC). It would go out when restarting, only to come back on.

After my second visit, the problem has been similar to what I first expirienced.

What things should be done, in what order?

Thank you!

Erlend