My zsara picasso hdi looses power whilst driving.it does not cut out and ticks over without a problem

I would check for an air leak in the fuel pipe.

It's due to discharged battery. Charge it using external charger or use jumpstart cables.

citroen zsara picasso brake light fuses

ya

check those links for the switch as well if you find the fuse to be OK

check throttle body / cable
needs adjusting

fauly. replace it

I also have a Peugeot 206 HDI and have had power drops on 2 occasions.
1st time caused by loose catalyst in exhaust... it was bouncing about so that it's honeycomb holes would align one minute, then drift out of line another minute.... sometimes really strangling power as it nearly blocked the exhaust..... I realised it was the catalyst after noticing it got really hot whilst the following exhaust remained cold as struggling up a hill.To check for this you can slacken the turbo to catalyst clamp so exhaust can escape .... and power should go back to full.(you can drive a short distance on open turbo without real problems... plus it quietens the exhaust reasonably enough)
2nd time was air getting into the diesel line ..... small bubbles would get sucked in whilst parked, due to fuel draining back to tank, and sucking on a loose fuel line joint on the squeezy priming bulb pipe.This caused short power dips initially but worsened over 6 weeks until the diesel filter would collect a pocket of air whilst parked.... causing it to completely stall a short while after starting..... Usually during acceleration, the fuel surge pulling the bubble through.
..... fixes .... 1st, I cut open and removed the catalyst, and re-welded casing shut (not needed in UK diesel test) and breathes better now :0) 2nd ..... done today, replaced bad pipe with high pressure fuel line and good pipe clamps. I've ordered a non return valve for the fuel line too (not that it needs it now) ..... to stop so much air getting in if it happens again, as I guess this is pretty bad for the high pressure pump, and a pain to replace if it goes ..... .... Beware of the very high fuel line pressures after the pump in running HDI engine.
The air mass sensor can be unplugged to test ... the engine will still run normally if no other problems.

We do not have this make in the USA so not sure we can provide any useful help. Sorry

check full cut off switch

it sounds like the catalytic convertor is blocked

renew the flexible hose connections at the tank end if fitted and not a plastic pipe going straight to sender unit .Sucking in air problem is one of THEM jobs .a right pain to find 99%of the time .but any flexible rubber pipes can and do go porous with age