I've got a 99 T5 w/5-speed stick with 64K miles (fresh out of warrantee) that I have had since new. It has just recently started making a noise that sounds suspiciously like detonation/pinging between 2000-3000 RPM under heavy acceleration. I'm running 91 Octane fuel and have had no "check-engine" lamp indications. After one call to an independent mechanic (I've had severe service quality problems with the dealer), I was told that (1) the car is equipped with a detonation sensor that should cause the computer to retard timing to prevent pinging and/or illuminate the check-engine lamp and (2) for 99s and newer, Volvo's proprietary VADIS system prevents independent mechanics from performing full diagnostics and resolution of problems like this.

Has anyone had a similar problem with a 99 or newer S/V70? If I am going to go to my dealer's service dept, they're the types that need to be told where to start looking for a problem. Without a fault code causing the check-engine lamp to light, they won't have a clue!

Thanks!