Tugboat

Hello all, We have are chasing a problem with a r34 Stagea in which the 4wd light is going off once the vehicle is started, but comes on again only after a few metres of travel. Code 78 (air bleed valve) is present in the ABS. Has anyone come across this before?, or can tell me where i might find this valve... The code clears with a scan tool, but reoccurs almost instantly. The vehicle has a PFC fitted as well, if that makes any difference. Tugboat