http://www.obd-codes.com/p0606
sounds kinda bad...
but dont panic JUST yet as said a weak battery can cause all sorts of undesired and phantom faults
on your multimeter you should have a letter 'V' with a wavey line next to it (Volts AC) and a letter 'V' with a solid straight line and a dotted line underneath (Volts DC)
you need to set your meter to the latter and you may have numbers within that section for instance 200m, 2000m, 20, 200, 400 (these are indications of the MAXIMUM voltage to be tested if you select 2000m and test a 12v system you will blow your meter)... for use on a 12v electrical system you should select the 20 denomination.
take readings directly across the battery terminals put the red lead on the '+' terminal and the black lead on the '-' terminal
post your readings for the following:-
keys out of ignition with no lights on (ensure the interior lights are off) you should get a reading of around 12.4v (if its less than about 11.8v then i would initially suspect a weak battery)
get somebody to start the car and note the reading when the engine is 'cranking' i.e. when the starter motor is running.
with the engine running note the reading this should be around 13.6-14.2v
please post your findings so that we may help more!
... or how also how to test the battery earth lead so could do with some help please...
im not convinced this would be a ground issue (although its nt unheard of) but your more than welcome to eliminate/include it using this method:- find a jump lead from a neighbour/friend clamp one end onto the '-' terminal and the other end directly to the body (one of the smaller bolts where the suspension top mount is bolted to the suspension turret/directly onto the engine or gearbox) this will confirm or deny battery earth lead issues...
