The dealer service guy showed me this trick (on the sly), claiming it will show whether any DTC fault codes are stored in the system. It works on my 2000 S80, and might be worth a try for others. Here's the procedure:
(1) start the car
(2) turn on the onboard computer to a display setting (say, average speed)
(3) hold down the "read" button on the turn signal arm for a few seconds and while still holding it down, do a quick double tap on the fog light button, then release the "read" button
(4) the message window will display the message "CHECKING DTCS", if you don't get this message, repeat (3) above until you do
(5) within a couple seconds, the message in my car changes to read "DTCS IN VEHICLE"
(6) now push the read button again to read each of the individual system modules (each push advances to read the next module sequentially). Mine reads as follows:
UEM DTC SET
I take the "DTCS IN VEHICLE" combined with "UEM DTC SET" to mean that I have a stored fault code in the Upper Electronics Module. It apparently does not give the actual code though, requiring the dealer's system to read and clear it.
I had not seen mention of this elsewhere, nor was I able to find any documentation of this function. I'm curious what readings others get. If nothing else, I hope this may help someone avoid unnecessary expense at the dealer.
Turn key to pos II or start the engine.
Press and hold down [READ] on the the turn signal lever, and press the rear fog light button 3 times quickly.
Press [READ] to advance to the next item.
BCM - Brake Control Module
SAS - Steering Wheel Angle Sensor
SRS - Safety Restraint System
ECM - Engine Control Module
AUM - Audio Module
and so on.
Benefit will verify that you have a stored DTC in a system that may not be supported in the DIM window.
Ready is echo complete, whereas Checking is host dependency is waiting.
TCM, ECM, etc. still need to go through further cycles to finish verification.
DIM, AUM, SRS, etc. are checked without driving or further data exchange.
The TCM, for example, will do solenoid checks, geartronic circuit grounding checks,etc., but inorder to determine gear pressure, vpm feedback, and so on, it must be driven.