Our 997 Carrera 4, PSM showed up on the dash among other things. Checked fuses all ok then ran the codes twice with my reader. PO 503 came up, vehicle speed sensor.
The car had reacted weird when braking, seemed to pull to the right so i changed the right side,. Ran the codes three times and all clear but the PSM light comes back on the dash, confusing, how does one get rid of that warning light. Used the reader o my GLK350 right after and it worked fine showed a code fot a camshaft pos' sensor so I know the reader is working.

 

What year? How many miles?

 

Check your brake light switch or replace it ….reseat it and see if that helps , I had the weirdest experience with mine.

 

PSM is the first error to show up from low voltage. How old is your battery, how often do you drive the car, and if not often, do you keep it on a Battery Tender?

If not battery, the next things to chect would be wheel speed sensors, then wheel bearings that when worn can deflect enough for the wheel speed sensor to not see the rotor vanes correctly.

You haven't installed different wheels or new tires have you?

 

Car is a 2006, 80K miles, it is driven on sunny days and stored winters, battery is maybe two yrs old and the car was driven in the last week. I just remembered I had a similar problem with my old Bimmer, tech told me to give it a good run on the highway and see what happens, problem solved . Gonna try that and the brake light switch?, I'll look it up on the net and see whats involved to change it

 

It is very simple as I had mine replaced awhile back, but try to go with the OEM one - about 30-50$ IIRC. Indy should charge no more than 200$, if that, all in FYI