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SPN 190 FMI 9 – Engine Speed Signal Not Available via CAN

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SPN 190 FMI 9 – Engine Speed Signal Not Available via CAN

This fault code indicates that the engine control module (ECM) is not receiving an engine speed signal via the Controller Area Network (CAN). This can lead to performance issues and potential derate behavior.

What This Code Means

SPN 190 FMI 9 signifies that the ECM is unable to detect the engine speed signal from the engine speed sensor through the CAN network. This lack of communication can result from a variety of issues, including wiring problems, module failures, or network resistance issues.

Why It Happens

Several factors can contribute to this code being triggered:

  • CAN Backbone Resistance: A typical resistance check of the CAN backbone should yield around 60 ohms. If the resistance is outside this range, it can cause communication failures.
  • Terminating Resistors: The absence or failure of terminating resistors at the ends of the CAN network can lead to signal reflection and communication errors.
  • Module Offline Behavior: If the ECM or another module on the CAN network is offline, it may not transmit or receive necessary signals, leading to this fault code.
  • Intermittent Harness Faults: Damaged wiring or loose connections can cause intermittent signal dropout, leading to sporadic occurrences of this fault.

 

How The Truck Typically Behaves

When SPN 190 FMI 9 is active, the truck may exhibit poor engine performance, and in some cases, it may enter a derate mode where power is significantly reduced to protect the engine. For example, a Freightliner Cascadia equipped with a DD15 engine may struggle to maintain speed or exhibit erratic RPM behavior.

Step-by-Step Diagnostic Approach

  1. Check CAN Backbone Resistance: Using a multimeter, check the resistance of the CAN network. It should be approximately 60 ohms. If not, assess the network for shorts or opens.
  2. Inspect Terminating Resistors: Verify that the terminating resistors are present and functioning correctly at both ends of the CAN network. A common issue is a missing or damaged resistor.
  3. Visual Inspection: Conduct a thorough visual inspection of the wiring harness connected to the engine speed sensor and ECM. Look for signs of wear, corrosion, or loose connections.
  4. Module Communication Check: Use a diagnostic scanner to check if other modules on the CAN network are communicating properly. If other modules are offline, further investigation may be needed.
  5. Signal Testing: If possible, use a scope to monitor the engine speed signal directly at the sensor and ECM while the engine is running to observe any dropouts.

Can You Keep Driving?

While it may be possible to drive the truck with SPN 190 FMI 9 active, it is not advisable. The potential for derate behavior and loss of engine performance can pose safety risks and lead to further damage. Addressing the issue promptly is recommended.

Frequently Asked Questions

  • What should I do if the engine speed signal returns after repairs? Monitor the system closely. If the code reappears, further diagnostic steps may be necessary to identify intermittent issues.
  • Can a faulty engine speed sensor cause this code? Yes, a malfunctioning engine speed sensor can lead to communication issues, but ensure to check the entire CAN network before replacing components.