Cummins fault code 285 is documented on this DiagTechPro library page for Cummins ISM CM871 (2007-09) engines, where it flags a Sae J1939 Multiplexing Pgn Timeout Error – Abnormal Update Rate condition (PID S231, SPN 639, FMI 9/9, Amber lamp). This 5-page PDF reproduces the manufacturer description, shop talk, component location and step-by-step troubleshooting so technicians can confirm and clear the code.
Cummins fault code 285 overview
Cummins defines this code as “SAE J1939 MULTIPLEXING PGN TIMEOUT ERROR – ABNORMAL UPDATE RATE” on the SAE J1939 Multiplexing Circuit. Normally, switches, accelerators and other components are connected to the engine electronic control module (ECM) directly through individual wires. Multiplexing allows those same components to be hard wired to an original equipment manufacturer (OEM) vehicle electronic control unit (VECU) or transmission electronic control unit (ECU) in the cab. Then component values and states from components such as sensors, accelerators and switches can be transmitted from the OEM VECU to the Cummins® engine ECM over the SAE J1939 Data link. Messages sent from OEM VECUs or transmission ECUs are received by the Cummins® engine ECM and used for controlling the engine.
Shop talk notes: Verify the electronic control module (ECM) calibration is correct. If necessary, recalibrate the ECM. When this fault code is active, some multiplexed devices may not function as desired.
Official document details
| Brand | Cummins |
| Model coverage | Cummins ISM CM871 (2007-09); Cummins ISX CM871 (2007-09) |
| System / Group | SAE J1939 Multiplexing Circuit — ISM CM871 fault codes |
| Fault code | 285 (SPN 639, FMI 9/9) |
| Source | TruckFaultCodes.com Cummins fault code reference (© 2017) |
| Pages | 5 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification (PID, SPN, FMI, lamp)
- Description
- Shop Talk
- Troubleshooting Steps
Applicable truck models and engines
This document applies to Cummins ISM CM871 (2007-09); Cummins ISX CM871 (2007-09) equipped diesel engines that log Fault Code 285. Always confirm engine calibration and use a Cummins diagnostic tool such as INSITE to read live data before starting repairs. Full specifications are published on the Cummins official website.
Who needs this Cummins fault code 285 manual
Heavy-duty truck technicians, fleet workshops and owner-operators diagnosing an electronic control module warning on ISM CM871 engines will use this sheet to verify the fault before parts are replaced.
The full PDF is available in the DiagTechPro manuals library; a free account is required to download.
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