Cummins ISB CM550 (1990-94) Fault Code: 285 PID: SID 231 SPN: 639 FMI: 9 J1939 Datalink Multiplexing

Circuit Description
Inputs, such as throttle pedals, switches, and sensors, can be communicated to the ECM over the J1939 datalink. Messages sent from the vehicle electronic control units (VECUs) are
received by the ECM and used for controlling the engine. Both the ECM and VECU must be
properly configured so that each device’s information is transmitted by the VECU and received
by the ECM.

Component Location
The ECM is located on the intake side of the engine, about mid-engine. The J1939 datalink
wiring and VECU(s) vary by OEM options.

Shop Talk
This fault occurs when the ECM is set up to receive information about a multiplexed device
from a VECU over the J1939 datalink and does not receive a message with that information. This fault can also be caused if the ECM does not receive the information fast enough to
control the engine properly. This condition can be caused by the J1939 datalink having an
electrical problem, a lack of terminating plugs on the J1939 datalink backbone, the ECM not
being set up to receive information, a multiplexed device that truly is not multiplexed, or a
VECU not being correctly set up to transmit information on one of its multiplexed devices.