CAT Engine 16399 Fault Code: Machine Security System Module : Abnormal Update Rate
Also called Anti-theft Component Status States : Abnormal Update Rate, Anti-theft Component Status States : Special Instruction, Machine Security System Module Abnormal Update Rate, Machine Security System Module Not Communicating on Link, Machine Security System Module abnormal update rate, Machine Security System Module not Communicating on Link, Machine Security System Module not communicating on link
Machine Security System Module : Abnormal Update Rate · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 16399 (SPN 1196 / FMI 9) means the Electronic Control Module has lost communication with the Machine Security System module on the data link. The warning lamp comes on, the code logs, and the engine will not start until communication is restored.
Critical severity. This code prevents the engine from starting at all. It is not a drivability nuisance, it is a no-start condition tied to the anti-theft/security module link, so the machine is down until the communication fault is fixed.
What does CAT Engine error code 16399 mean?
, CAT 16399 fires when the ECM cannot establish or maintain communication with the Machine Security System (MSS) module over the CAN data link (also called the J1939 data link). This module is part of the machine's anti-theft/security system, and the ECM depends on it to confirm the engine is authorized to run.
Because starting is gated by this handshake, a communication failure is treated as a serious fault: the warning lamp illuminates, the code logs, and the ECM blocks engine start until the link issue is resolved.
The underlying data link is a shielded twisted pair circuit that needs proper termination resistance to carry data reliably. If wiring, connectors, or terminating resistors are damaged, the signal becomes intermittent or unreadable, which the ECM interprets as a communication loss.
What triggers a CAT Engine 16399 code?
Communication with the machine security system must be established within 3 seconds after ECM powerup. If communication is established and then stops for 1 second, the code will also generate. Separately, the data link requires a total resistance of 60 Ohms across the two data wires (made up of two 120 Ohm terminating resistors at opposite ends of the circuit) for reliable data transfer; a measured resistance greater than 10 Ohms is also listed as a possible cause of this code.
Common causes of 16399
- Damaged connectors and/or wiring in the data link circuit
- General problems with the wiring harness
- Faulty terminating resistors (should provide 60 Ohms combined resistance from two 120 Ohm resistors)
- Short circuit in the harness or in a connector
- Data link connector power connections not wired correctly
- Diagnostic connector not receiving the correct voltage
- Resistance in the circuit greater than 10 Ohms
- Faulty ECM
- Faulty electronic service tool
How to troubleshoot CAT Engine 16399: first checks
- , Inspect all connectors related to the data link and the Machine Security System module for corrosion, damage, bent pins, or loose pins
- Check the harness for chafing, pinched wiring, or physical damage, remembering that the data link wiring must be shielded twisted pair cable if replaced
- Verify the terminating resistors are present and functioning at opposite ends of the data link circuit
- Check the diagnostic connector for correct voltage supply
- Measure resistance across the data link circuit and confirm it is not greater than 10 Ohms
- Confirm the data link connector power connections are actually wired as intended
- If wiring, connectors, and resistors all check out, suspect the ECM or, if using a scan tool to diagnose, the electronic service tool itself
How the code clears
No separate clearing step is listed beyond fixing the root cause. Once communication with the Machine Security System module is restored and stable, the ECM should allow the engine to start again. There is no stated manual reset procedure independent of repairing the wiring, connectors, terminating resistors, or ECM.
Affected models and serial ranges
16399 appears in our records across 6 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C11 | Serial range not listed in source records |
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C18 | Serial range not listed in source records |
| C27 | Serial range not listed in source records |
| C32 | Serial range not listed in source records |
Frequently asked questions
Can I bypass CAT code 16399 to start the engine anyway?
No bypass is described. The ECM is designed to block engine start when it loses communication with the Machine Security System module, since that module is part of the anti-theft system. Attempting to bypass security-related logic is not a supported repair path.
What does SPN 1196 FMI 9 mean on a CAT engine?
SPN 1196 identifies the Machine Security System Module parameter, and FMI 9 indicates an abnormal update rate on the data link, meaning the ECM is not receiving communication at the expected rate or at all. Together they correspond to CAT fault code 16399.
Why won't my CAT engine start with code 16399 active?
The engine will not start because the ECM requires confirmation from the Machine Security System module over the data link before allowing a start. If that communication is lost, the ECM logs 16399 and disables features that depend on the link, including start authorization.
Is 16399 an electrical problem or an ECM problem?
It can be either. Listed causes range from damaged connectors and wiring, harness problems, and faulty terminating resistors to resistance issues in the circuit or a bad ECM. Diagnosis typically starts with the wiring and connectors before moving to the ECM.
What is the Cat Data Link and how does it relate to this code?
The Cat Data Link is the standard link the ECM uses to talk to a diagnostic scan tool for status, diagnostics, and configuration. This code also checks for open or short circuits in that data link, since problems there can disrupt the communication the ECM needs.
What resistance should the data link have?
The data link should measure 60 Ohms across the two wires, made up of two 120 Ohm terminating resistors placed at opposite ends of the circuit. Some diagnostic paths flag a fault if resistance is greater than 10 Ohms, so both figures are relevant depending on which check you are running.
Which CAT engines can set code 16399?
This code applies to the C11, C13, C15, C18, C27, and C32 engine models when equipped with a Machine Security System.