How to Troubleshoot SPN 973 FMI 9 Code on a 2014 Freightliner

If you own or drive a 2014 Freightliner truck, you may encounter a code that reads SPN 973 FMI 9 on your dashboard. This code indicates that there is a problem with the engine retarder selection, which is a feature that helps you slow down the vehicle without using the brakes. The FMI 9 means that the signal from the engine retarder switch is not updating at the normal rate, which could be caused by a wiring issue, a faulty switch, or a software glitch.

In this article, we will explain what the engine retarder is, how it works, and how to troubleshoot the SPN 973 FMI 9 code on your 2014 Freightliner.

What is the Engine Retarder?

The engine retarder, also known as the engine brake or the Jake brake, is a device that uses the engine’s compression to create resistance and slow down the vehicle. The engine retarder is activated by a switch on the steering wheel or the dashboard, and it can have different levels of intensity depending on the model and configuration of the truck.

The engine retarder is useful for reducing the wear and tear on the brakes, especially when driving downhill or in heavy traffic. It also improves the fuel efficiency and the safety of the vehicle, as it reduces the risk of brake fade or overheating.

How Does the Engine Retarder Work?

The engine retarder works by altering the timing of the exhaust valves in the engine. When the engine retarder is off, the exhaust valves open normally after the combustion stroke, allowing the exhaust gases to escape and the piston to move up. When the engine retarder is on, the exhaust valves open earlier, before the piston reaches the top of the cylinder. This creates a back pressure that pushes the piston down, creating resistance and slowing down the engine.

The engine retarder can be controlled by the driver through a switch that sends a signal to the engine control module (ECM). The ECM then adjusts the timing of the exhaust valves according to the desired level of retardation. The ECM also communicates with other modules in the vehicle, such as the cruise control module (CCM) and the brake control module (BCM), to coordinate the operation of the engine retarder with the other braking systems.

How to Troubleshoot the SPN 973 FMI 9 Code?

The SPN 973 FMI 9 code means that the ECM is not receiving the signal from the engine retarder switch at the expected rate. This could indicate a problem with the wiring, the switch, or the software of the ECM or other modules. To troubleshoot this code, you should follow these steps:

  1. Check for multiple codes: If you have other codes related to the battery voltage, the CAN line, or the adaptive cruise control, you should troubleshoot those first, as they could be affecting the communication between the modules.
  2. Check the wiring: Inspect the wiring harness and connectors for any signs of damage, corrosion, or loose connections. Pay special attention to the wires that connect the engine retarder switch to the ECM. If you find any problems, repair or replace the wiring as needed.
  3. Check the switch: Test the engine retarder switch for continuity and resistance using a multimeter. If the switch is faulty, replace it with a new one.
  4. Check the software: Connect a diagnostic tool to the vehicle and check the software version of the ECM and other modules. If the software is outdated or corrupted, update or reprogram the software using the manufacturer’s instructions. You may need to contact a dealer or a service center for this step.

If none of these steps resolve the issue, you may have a more serious problem with the ECM or other modules, and you should seek professional help.

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