<!-- from fixya rte -->2001 exterra brake booster - 2001 Nissan Xterra

try this link might help you find out.
Turn signal flasher location for 2001 Nissan Exterra Google Search

Jack, Have not done a SAAB brake booster myself, hoping links below will help you out. Check the attached links,instruction and guides, Good luck
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Walk me through brake booster replacement
http://www.thesaabsite.com/faqs/FAQ--brakes-contributor--brake-pump-booster-issues-%26-removal.html?id=1300
9 5 Brake booster replacement the easier way
saab 9 3 brake booster replacement Google Search

Hard brake pedal when applied with the engine running. A quick test for the vacuum assist booster is to shut off engine, pump brake pedal 3 or 4 times and hold on the last pump, start engine and see if pedal drops a bit....if you detect a problem with booster you should check for adequate engine vacuum supply to booster when idling . You can sometime hear a hissing or air leaking when applying brake pedal with engine running if booster is defective

You will have to drain and remove the master cylinder. Remove vacuum lines from booster. Than disconnect your brake pedal from the brake booster. This in done from inside the car. After you disconnect your brake pedal, there should be four nuts that hold the booster the the bulk head. Remove those and carefully remove booster from car from under the hood. Install in reverse order and bleed your brake system.

Lost Vacuum to Brake Power Booster

Check vacuum hoses from intake to booster,
& booster check valve

http://www.ebay.com/sch/items/?_nkw=2001+olds+aurora+repair+manual&_sacat=&_ex_kw=&_mPrRngCbx=1&_udlo=&_udhi=&_sop=&_fpos=&_fspt=1&_sadis=&LH_CAds=&satitle=2001+olds+aurora+repair+manualHere's some repair manuals.

Did you brake into the hydraulic system at any point? If so them Moose had the answer. Did you crank the truck in park and then push on the pedals so the brake assist booster can do its job? Check the level of fluid at the brake resevoir. A low level should be cause for a refill. Did you leave any brake bleeder valves open? I assume it was the fron disc that were reaplced. If so hopefully it hasn't blown a brake caliper . If so replacement or rebuild will be the answer. You have definitely lost pressure so look for looks on the inside of all wheels. Also try cranking your truck and then pump the brakes to allow the brake assist to lend a hand and do its job.

Do you by any chance hear a hissing noise from under the dash? If so, yes, you have a bad booster. For it to do what you're saying, it would almost have to have a vacuum leak. However, if there is a problem with something in the ABS system, you should have an ABS warning light on. Also, ABS can make the pedal fade, but I've never heard of it making the pedal hard. Your diagnosis of a brake booster does sound likely, but I'll admit I can't be sure -- this is an odd one.

That sound you hear is coming from the Vauum Brake Booster...Sooner or later the Brake Pedal will get hard, because the seal inside of the Brake Booster is leaking..And the only way to repair it, is , to replace the Brake Booster...But also check your Vacuum Hose that is instaaled on your Brake Booster..It goes from the Brake Booster, which is behind the Master Cylinder...From there to the Intake Manifold...Just make sure that there are no cracks in that hose, and make sure it is on all the way...because if the hose is bad, then thats all you will have to replace....Goodluck...

did you bleed the master cyl. before or during installation? bleed brakes in proper order?RR LR RF LF? does it have a power booster between master cyl.& firewall?check for vacuum to booster.when ABS isn't working you should still have brakes.suspect power booster diaphram.