SPN 639 - FMI 2 (Fault Code 426)

J1939 Network #1 - Data Erratic, Intermittent, or Incorrect

SAE J1939 Data Link 1 Circuit

Fault Code: 426
PID(P), SID(S): S231
SPN: 639
FMI: 2/2
Lamp: None

REASON: Communication between the engine control module (ECM) and another device on the SAE J1939 data link has been lost.

EFFECT: None on performance.

Circuit Description:
Normally, switches, accelerators, and other components are connected to the engine 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® ECM over the SAE J1939 data link.

Messages sent from OEM VECUs or transmission ECUs are received by the Cummins® ECM and used for controlling the engine. The Cummins® ECM and OEM VECUs must be configured properly so that proper operation of the multiplexed components will occur.

Component Location:
The SAE J1939 data link wiring and the SAE J1939 devices vary by OEM options.

Conditions for Running the Diagnostics:
This diagnostic runs continuously when the keyswitch is in the ON position or when the engine is running.

Conditions for Setting the Fault Codes:
The Engine Control Module (ECM) detected an open or short circuit condition in the J1939 data link harness.

Action Taken When the Fault Code is Active:
• The ECM logs the fault code immediately when the diagnostic runs and fails.
-The multiplexed device will not operate.

Conditions for Clearing the Fault Code:
• To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
• The fault code status displayed by the recommended Cummins® electronic service tool or equivalent will change to INACTIVE immediately after the diagnostic runs and passes.
• The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
• The “Reset All Faults” command in the recommended Cummins® electronic service tool or equivalent can be used to clear active and inactive faults.

Shop Talk:
Possible causes of this fault code include:
• Shorted or open J1939 data link wiring.

Read More:
SPN 97 - FMI 4 (Fault Code 429)
SPN 97 - FMI 3 (Fault Code 428)


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2 Responses to "SPN 639 - FMI 2 (Fault Code 426)"

  1. My truck gave me amber code and check engine code, eveventually derated me to 55. After 7 minutes the check engine went out and the amber stays on. When I stopped and check code ,its cruise, spn 639 fmi 2. Why does this keep happening.