Thanks for the feedback Richard, funnily enough I looked at the wiring diagrams (which only seem to show the downstream sensors!), but I noticed that fuses 13 and 14 seemed to be a common factor. So the first thing I looked at today was fuse 13 and guess what it was blown. I replaced it and it blew again. So I am in a way quite relieved as the obvious common problem seems to be a great starting point. So my question is could this be a shorted heater circuit - does that happen?? or do you know of any obvious places to look to trace the short? Thanks again
Apologies for late reply, just noticed your post above. As you say a good clue allowing the search for cause to be narrowed. Looking downstream from engine fuse 13 we have
all four oxygen sensor heaters (sensors themselves within connect direct to PCM as with cam sensors), evap cannister purge valve and all four cam solenoids. Once the fuse blows all these feeds would be lost explaining the fault codes you originally mentioned. Although any one or its wiring could be at fault, it does look like the oxy sensor heaters would be first place to look if only because they are under greatest thermal stress.
Note my wiring diagram shows both upstream and downstream oxy heaters fed from same fuse. Cannot find what engine fuse 14 you mention feeds other than its labeling as VPR3 to PCM, so unless you know otherwise that may be a red herring.
Good luck with search!
ETA: it may be possible to narrow search down on the oxy sensors, assuming one is faulty and that fuse 13 blows before engine started. The downstream pair are fed directly from this fuse with yellow/white cable that splits to feed sensor heaters each side. The upstream pair are also fed by another yellow/white cable from fuse 13, but in this case via pin 16 on engine loom connector C58 (which also feeds cam solenoids). It's possible if you broke this connector then tried replacing the 15 amp fuse to check whether it still blows, it would allow further narrowing down of root cause. Unsure if you need engine running to prove and if it would start at all with connector broken though, hence comment at start of paragraph.
