It's probalby a broken cable - I had this problem and bypassed the existing cable from the rear left sensor. I reconnected back to the loom at around the front door as it runs along the left front door rim (underneath the plastic cover that normally has Saab printed on it. You need to know which cables to cut and at present I can't remeber the colour coding. If you need more help, let me know.
Rodp, December 2008
