Cummins X15 CM2350 X116B Performance Series (2018 & Newer) Fault Code: 8634 PID: SPN: 12868 FMI: 9/9 TSC1 Control Purpose P7 Inhibit Command – Abnormal Update Rate

Lamp:
None

Reason:
The ECM expected information from a multiplexed device but did not receive it soon enough or did not receive it at all.

Effect:
At least one multiplexed device will not operate properly.

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 OEM ECM over the SAE J1939 data link. Messages sent from OEM VECUs or transmission ECUs are received by the OEM ECM and used for controlling the engine. The OEM 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 Code:
1. The Engine Control Module (ECM) did not receive a message from a multiplexed device.
2. 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:
1. The ECM illuminates the amber check engine lamp immediately when the diagnostic runs and fails.
2. The multiplexed device will not operate.

Conditions for Clearing the Fault Code:
1. To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
2. The fault code status displayed by the recommended diagnostic tool or equivalent will change to inactive immediately after the diagnostic runs and passes.
3. The ECM will turn off the amber check engine lamp immediately after the diagnostic runs and passes.
4. The “reset all faults” command in the recommended diagnostics tool or equivalent can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop Talk:
1. When this fault code is active, some multiplexed devices can possibly not function as desired.
2. Possible causes of this fault code include:
A. When the ECM is set up properly (components enabled and OEM VECU source addressed correctly) to receive information from an OEM VECU, but the OEM VECU is actually transmitting a message that says that component is not available for multiplexing. This can be caused when a multiplexed component is enabled in the ECM, but the OEM VECU source address of the VECU transmitting the component message is incorrect in the OEM ECM, or the OEM VECU is not set up to transmit the multiplexed component message.
B. This fault can also be caused by a bad J1939 data link connection between the OEM VECU and OEM ECM, a bad connection between the component and the OEM VECU, bad OEM VECU or bad OEM ECM. It may be necessary to contact the OEM for proper multiplexing configuration. It is possible to use the recommended diagnostic tool or equivalent to monitor multiplexed components.
C. It is possible to use the recommended diagnostic tool or equivalent to monitor multiplexed components.