If that light is on, it means the system has detected a fault and has a message waiting for you about what the fault is; all you have to do is ask for it. We need that clue in order to have a direction to go with our diagnostics. Here is the procedure for retrieving codes from the ABS self-diagnostic system.
http://www.swedishbricks.net/700900F...de%20Retrieval
Carry out this simple procedure from start to finish, write down the 3-digit code(s) that it gives you, then look up the code(s) in the fault table to see what they mean. Then report back here and we can advise on what to do about it based on what the actual specific issue is.
