1999 Volvo S80 Car Starter

Do you have a good strong crank whe it is cranking over or is it a very slow crank? Do any warning messages come on the instrument cluster when it wont start? Why did you have the exhaust system replaced?

I dont blame you, those guys can be pretty expensive =O! And a strong cranking engine indicates the battery is working properly. Now I need to know if your problem happens only with one key or do you notice it with both keys? If it is only with the one key then the transponder chip in the key is failling and the only fix for that is to replace and program a new key. If the problem is with both key, then for some basics you need to make sure there are no other keys with transponders on them attached to the same key ring. If you have something like a fast track pass near the ignition switch like on top near the instrument cluster then move it somewhere else. Those things will interfere with antenna ring and key communication. Now a couple of things I forgot to ask? When you are cranking whether it starts or does not start, does the RPM needle fluctuate on you? Also has the check engine light come on or was it on before and then it went out? If the light was on or curently on, have you had it scanned for trouble codes? If not, can you get it scanned and post the codes on here? Some place like AutoZone may be able to scan it for you at no charge? Let me know please.

If the needle soes fluctuate and jumps around. Have him look at TNN# 28-0011 for rerouting battery cable away from the RPM sensor. It is an old TNN but see what he finds first during his diagnosis.
Good luck and keep me posted.