Good Morning, just a general question concerning my 1993 Volvo 960 4drsd with 215K. 2 days ago CEL came on while driving. car still runs fine, Went to pull codes and red led won't flash at al, can't even get it to pull 1-1-1. Disconnected battery last night and touched cables together overnight for 13 hours total. Hooked up battery again this morning and started vehicle, CEL came on immediately and still cannot retrieve codes in any of the diagnostics ports. Test drove vehicle for 15 miles and it ran perfect like it always does. Only knock on this vehicle is 19 MPG. Is their any Volvo Gurus out there that can maybe point me in the right direction ?

 

see if the probe wire is making a good connection and in the correct port, plus check where the wire goes into the diagnostics box - they can fray/break where the wire enters the box.