triangle lite always on, P1618 code, check engine lite on 1999 Volvo S80

orange triangle lite is always on.
P1618 code.
engine lite appears.
using cruise control, shifts into second.
247,000 miles

Asked by for the 1999 Volvo S80
I'm trying to troubleshoot the same code, although slightly different symptoms.
What I've found so far is that this Code relates to the transmission, albeit indirectly it seems. Its a code that's telling you that the transmission is in Limp mode, or will be soon. And there are various factors that can trip this code, the most common it seems is a failing speed sensor in the ABS Control module (engine bay) connect to ABS pump. This module has to be replaced or rebuilt.
Other symptom is a common one associated with a cable fault, wring loose, or some such thing, relating to the connecting wiring between transmission control module and engine computer.
Other people are reporting that if you haven't changed tranny fluid and filter in a quile or ever, that this can trip this code too.
If you car isn't in limp mode with this code, you're lucky.
2 more answers
I believe this is indicating that the transmission module has detected a fault with the transmission and is requesting that the Check Engine Light be turned on. Check the diagnostic codes in the transmission.
This code indicates that there is a transmission code that needs to be accessed. You may have used a generic scanner, it still may be able to access the transmission computer but it may not, then you will have to go to a shop that has a Volvo capable scanner.