Detecting Conditions
WARNING: This page is about a different car, the 2003 Toyota Prius, 2002 Toyota Prius, and 2001 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
DTC 54 may be set if after turning the ignition switch ON, a short or open circuit in pressure switch (PL) continued for more than 1 second. Or, after turning the ignition switch ON, open in pressure switch (PH) continued for more than 1 second.