"Brake failure stop safely" and limp mode - see photo

[danc]

My 2006 auto XC90 (pre-facelift model, 50k miles) has intermittently started showing a couple of warning messages, shortly followed by limp mode.

It's now done this three times in the last three months, as follows:

1. Car drives normally, then from moving off from a standing start, clunks into limp mode (low power, remains in low gear and 40mph max, D symbol on dashboard changes to dash or "-" symbol - see photo)

2. Immediately, "Anti-skid Service Required" message displayed on dashboard, amber warning light

3. Few seconds later, "Brake Failure Stop Safely" message displayed, red warning light, rev, mph, temp dials stay at 0

4. Limp back home, switch engine off, then fails to re-start for at least an hour.

I've experienced no loss of braking (that I can tell).

My local Volvo specialist says the codes show faults relating to:

1) a brake pressure sensor and / or
2) the steering sensor

Both are expensive to replace, particularly without knowing which one is at fault. The car is back with me for now although it now feels far from reliable.

Has anyone experienced this sequence of events? Ideas on where to head next with this, appreciated.