XC90 2.5T AWD L5-2.5L Turbo VIN 59 B5254T2 (2003)
For faults when messages cannot be sent on the MOST network, diagnostic trouble code (DTC) ICM-DC02 is stored Causes of this fault may be that:
a control module, except the infotainment control module (ICM), has a defective optical connector
a control module has an internal fault, which means that the optical connection stops working
a control module on the MOST network is not powered. If there is no power supply, the optical connector stops transmitting light
the optical cable is damaged or there is a break in it. This fault may occur if the bend radius of the cable is too small or the cable has been folded
there is dirt or oil on the optical connectors which impedes the light
the connection to a control module has come loose
the fiber optic terminals in the connector are cross-connected
there is a loose connection because the fiber optical wiring is incorrectly installed or the fiber optic terminal pin has been pressed back in the
a bridging connector has come loose or is damaged.
Ring break diagnostics are used to remedy diagnostic trouble code (DTC) ICM-DC02. If a break is discovered in the MOST network after running a ring
break diagnostic, diagnostic trouble code (DTC) ICM-DC01 will be stored in the infotainment control module (ICM). If this is the case, the position of
the open-circuit and control module location, can be read off from the infotainment control module (ICM).
Ring break diagnostics
This function is important when fault-tracing the MOST network. Ring break diagnostics are used when there is an open-circuit in the MOST network
and diagnostic trouble code (DTC) ICM-DC02 has been stored in the infotainment control module (ICM).
During fault-tracing, all control modules transmit a message to the infotainment control module (ICM) in reverse order in relation to the position on the
network. This means that the antenna module (ATM) is first, not last. The control module which is not working will not transmit an answer to the
infotainment control module (ICM). This also means that the control modules connected after the defective control module will be unable to transmit a
message to the infotainment control module (ICM).
The same applies in the event of an open-circuit in the fiber optic cable in the MOST network. None of the control modules before the open-circuit will
be able to send their message to the infotainment control module (ICM). The infotainment control module (ICM) is then able to calculate the position of
the open-circuit from the incoming messages.
Hint: It is important to know which control modules are connected and in what order to identify the control module which sends each message.
A MOST network contains all eight control modules.
There is an open-circuit in the wiring between the phone module (PHM) and the MD module (MP1). See the illustration.