SPN 110 FMI 9 – Coolant Temperature Signal Not Available via CAN

This code indicates that the engine control module (ECM) is unable to receive the coolant temperature signal via the Controller Area Network (CAN). This can lead to improper fuel mapping and potential engine derate.

What This Code Means

SPN 110 FMI 9 signifies a loss of the coolant temperature signal, which is critical for the ECM to make informed decisions about fuel delivery and engine performance. Without this signal, the ECM cannot accurately assess engine temperature, which can result in inefficient operation.

Why It Happens

This issue can arise from several factors, including sensor failure, wiring harness integrity problems, or issues within the ECM itself. The coolant temperature sensor may be faulty, or there could be a break or short in the wiring that prevents the signal from reaching the ECM. Environmental factors, such as corrosion, can also contribute to these failures, particularly in older Freightliner Cascadia models equipped with DD15 engines.

How The Truck Typically Behaves

When SPN 110 FMI 9 is active, the truck may exhibit symptoms such as erratic engine performance, poor fuel economy, and in some cases, a derate condition. The ECM may trigger a derate to protect the engine from potential overheating, limiting power output and affecting drivability.

Step-by-Step Diagnostic Approach

1. Initial Scan: Use a diagnostic scanner to confirm the SPN 110 FMI 9 code and check for any related codes that may indicate additional issues.
2. Sensor Check: Inspect the coolant temperature sensor for physical damage or corrosion. Perform a resistance test on the sensor according to manufacturer specifications; a faulty sensor will often show readings outside the expected range.
3. Wiring Inspection: Examine the wiring harness for signs of wear, fraying, or disconnection. Pay special attention to connectors; corrosion can cause intermittent signal loss.
4. ECM Communication: Verify that the ECM is functioning correctly and is able to receive signals from other sensors. Check the CAN bus for any communication errors that may affect the coolant temperature signal.
5. Test Drive: After making repairs, take the truck for a test drive while monitoring the coolant temperature data through the diagnostic tool to ensure the signal is now available and functioning as expected.

Can You Keep Driving?

While it may be tempting to continue driving with SPN 110 FMI 9 active, it is not recommended. The risk of derate and potential engine damage is significant. If the coolant temperature cannot be monitored, the ECM cannot effectively manage engine performance, leading to overheating or other serious issues.

Frequently Asked Questions

• What should I do if the coolant temperature sensor is faulty?
  Replace the sensor with a manufacturer-approved part to ensure compatibility and reliability.
• How can I prevent this issue in the future?
  Regular maintenance, including inspections of the wiring harness and connectors, can help prevent this issue from arising.
• Is it safe to drive with this code?
  No, it is not safe to drive with this code. Address the issue as soon as possible to prevent further damage.