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SAE J1939 Data Link Multiplexing
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Overview
| CODE | REASON | EFFECT |
| Fault Code: 285 PID: S231 SPN: 639 FMI: 9 (J1587), 9(J1939) LAMP: Amber SRT: |
The ECM expected information from a multiplexed device but did not receive it soon enough, or did not receive it at all. |
At least one multiplexed device will not operate properly. |
 SAE J1939 Datalink Multiplexing Circuit
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Circuit Description
Inputs, such as accelerator pedals, switches, and sensors can be communicated to the ECM over the SAE J1939 data link. Messages sent from the vehicle electronic control units are received by the ECM and used for controlling the engine. Both the ECM and vehicle electronic control units must be properly configured so that each device’s information is transmitted by the vehicle electronic control unit and received by the ECM.
Component Location
The ECM is bolted to the intake side of the engine between the air horn and the front of the engine. Refer to Procedure For component location information 100-002 (Engine Diagrams) in Section E.
Shop Talk
This fault occurs when the ECM is set up to receive information about a multiplexed device from a vehicle electronic control unit over the SAE J1939 data link 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 SAE J1939 data link having an electrical problem, a lack of terminating plugs on the SAE J1939 data link backbone, the ECM not being set up to receive information, a multiplexed device that truly is not multiplexed, or a vehicle electronic control unit not being correctly set up to transmit information on one of its multiplexed devices.
Refer to Troubleshooting Fault Code t05-285
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