My son and daughter are en route to California from Massachucetts as I write.They left yesterday in his !998 S70glt, 88K. I thought the car was ready to go and lo and behold the old CEL went on the other day. My Volvo guys are on vacation so I had no choice but to go to the local dealer to see what code was kicking in. I don't have the number(it's with them in the car) but I was told it was the anti-knock sensor code. The tech reset it and took it for a spin without it going back on, seemed to think it should be good to go,said I got lucky because to replace it you need to take off the exhaust manifold. Just got a call from the kids,they're almost in Nashville and the darn CEL is back on. Said the car appears to be running normal.Any info out there about this sensor,could it possibly be from some bad fuel? Will that CEL stay on until it's reset,or is there a way to have it reset itself somehow,maybe a tank of 91 octane? Any harm done ignoring it for a few more thousand miles? I told them to keep on trucking for now. Any help would be greatly appreciated.Thanks.

 

I would run high test fuel in it and maybe even put a bottle of Techron in there.
The code will need to be cleared.