SPN 120 FMI 13 – J1939 Retarder Fluid Message is missing or not available Fault Code (Symptoms, Causes & Fix)
The SPN 120 FMI 13 fault code indicates a communication error where the J1939 Retarder Fluid Message is missing or not available. This diesel engine fault code suggests that the Engine Control Module (ECM) is not receiving the necessary data from the retarder control module, which can affect the retarder system's performance.
What SPN 120 FMI 13 Means
The SPN 120 FMI 13 diagnostic trouble code signifies a loss of communication regarding the retarder fluid message over the J1939 data link. The ECM expects to receive this message to manage the retarder system effectively. When this message is absent, it triggers the fault code, indicating a potential issue in the communication pathway or the retarder control module itself.
Common Causes of This Fault Code
- Faulty retarder control module
- Damaged or corroded J1939 communication wiring
- Loose or corroded connectors
- Software issue in the ECM or retarder control module
Symptoms Drivers May Notice
When the SPN 120 FMI 13 fault code is active, drivers may notice a lack of retarder functionality, which can affect vehicle braking performance. Additionally, there might be warning lights on the dashboard indicating a communication issue.
How Technicians Diagnose This Fault
Technicians begin by performing a visual inspection of the J1939 communication wiring and connectors for any signs of damage or corrosion. Next, they conduct a continuity test on the J1939 data link circuit to ensure signal integrity. Voltage reference testing is performed to verify proper power supply to the retarder control module. Using diagnostic software, technicians check for additional fault codes that may indicate broader communication issues. Finally, they verify ECM data to ensure it aligns with expected parameters.
Common Misdiagnosis
Technicians often misdiagnose this fault by assuming a mechanical failure in the retarder system without checking communication lines. Another common mistake is replacing the retarder control module without verifying the integrity of the wiring. Overlooking software-related issues that could be resolved with an update is also a frequent error.
Can You Keep Driving?
While it may be possible to continue driving with the SPN 120 FMI 13 fault code active, it is not advisable due to the potential impact on braking performance. The retarder system may not function correctly, which could lead to increased wear on the primary braking system and reduced vehicle control.
Mechanic's Diagnostic Tip
Before replacing any components, ensure all connectors are clean and secure. A simple cleaning and reconnection can often resolve communication issues without the need for part replacement. Always verify the latest software updates for the ECM and retarder control module, as these can address known communication problems.
Frequently Asked Questions
Q1: Can a software update fix the SPN 120 FMI 13 fault code?
A1: Yes, a software update can sometimes resolve communication issues if the fault is related to outdated or corrupted software.
Q2: What tools are essential for diagnosing this fault code?
A2: A multimeter for continuity and voltage testing, along with diagnostic software to read and clear fault codes, are essential tools.
Q3: Is it necessary to replace the retarder control module if this fault code appears?
A3: Not necessarily. Always perform thorough electrical testing and check for software updates before replacing the module.
