MOST ring breaks in NGI systems
Posted to Technical Tips Forum on 5/18/2013
21 Replies
This post will most likely be of interest to GM techs only
at this time as this technology has not filtered down to the
aftermarket yet.
Finding MOST ring breaks can be done without too much
trouble if you have a good idea how the system operates. The
MOST network is a chain type unidirectional network. The
radio is used as the MOST master module in most cases. It is
also used as the MOST to low speed GMLAN gateway module and
is usually assigned MOST module 1 position. During a ring
break, communications will cease on the nework and only node
ID's will be reported.
If a MOST ring break occurs, the radio will report U0028. To
determine the site of the ring break, check the MOST network
parameters. The LAST WORKING MODE ID will always be present,
but the SURROGATE MOST MASTER NODE UPSTREAM POSITION will
only be present while the ring break is active. When the
ring break occurs, the module in the ring after the break
will report itself as the surrogate MOST master module. This
is important as the unidirectionality of the network will
point out the break area as between the surrogate MOST
module and the MOST master module.
By looking at the LAST WORKING MOST MODE ID numbers reported
and the position of the MOST module that declared itself as
the SURROGATE MOST MASTER NODE, the ring break position can
be estimated from the driver's seat before intrusive
testing.
James from Florida
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