The Cummins ISM code 426 manual is a 8-page diagnostic PDF for the J1939 datalink communication on the ISM CM570 (1999–2002) engine. It explains the J1939 datalink that lets the electronic control module (ECM) exchange messages with other devices on the vehicle bus, and this fault carries no warning lamp.
Cummins ISM code 426 document details
| Brand | Cummins |
| Model coverage | ISM CM570 (1999–2002) |
| System / group | J1939 datalink communication — DTCs |
| DTC number | 426 |
| PID / SPN | S231 / 639 |
| FMI | 2/2 |
| Warning lamp | NONE |
| Pages | 8 |
| File format | |
| Language | English |
Document table of contents
- Circuit description and component location
- Shop talk on communication loss causes
- Reading J1939 devices with the diagnostic tool
- Datalink wiring and termination checks
Applicable truck models
This procedure applies to the ISM CM570 (1999–2002) engine and the shared CM570 fuel-system platform found in on-highway trucks. The same fault-code logic is carried across related CM570 engine families of that era. For engine identification and factory service references, see the manufacturer at the Cummins official website.
Who needs this Cummins ISM code 426 manual
The document lists ABS controllers, automatic-shift transmissions, ASR systems, electronic displays, information systems, service tools and VECUs as devices that communicate over the J1939 datalink. It records that the fault sets when the ECM starts communicating and then can no longer transmit, with likely causes including unplugging a service tool before keying off, an intermittent datalink, or a device tying up the bus with too many messages. The tree uses the diagnostic tool to read which devices are sending input.
This guide suits diesel technicians and workshop owners who face a no-lamp communication fault and need to identify which J1939 device or bus segment dropped off. It reads as fault code 426 troubleshooting steps for the J1939 datalink communication, keeping the diagnosis ordered and evidence-based.
The full PDF is available in the DiagTechPro manuals library, where a free account is required to download it.
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