Freightliner SPN639FMI2 Fault Code: Data is erratic, intermittent, or incorrect.
Also called SPN 639/FMI 2 — PCC, The ICC5 has detected a problem with communications on the chassis CAN., The ICC5 has detected a problem with communications on the chassis Controller Area Network (CAN).
Data is erratic, intermittent, or incorrect. · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 639/FMI 2 means the Instrument Cluster, Connect 5 (ICC5) module has detected a problem with communications on the chassis Controller Area Network (CAN), with no messages received on the chassis CAN. It sets when battery voltage is within normal operating range, the keyswitch is ON, and the ICC5 is awake. The result is that the instrument cluster cannot talk to other vehicle ECUs, which can knock out gauges and steering wheel switches.
Medium severity. This is a communication fault, not an active mechanical failure, so the truck can often still be driven. But losing gauges, warning lights, or steering wheel switches means you lose visibility into other systems, so it should be diagnosed before continuing normal operation, not ignored.
What does Freightliner error code SPN639FMI2 mean?
SPN 639/FMI 2 is set by the ICC5 module when it detects no messages being received on the chassis Controller Area Network (CAN), the shared data network that lets the instrument cluster and other vehicle Electronic Control Units (ECUs) talk to each other.
The chassis CAN carries information like engine data, warning lamps, and switch inputs across the truck's electronic systems. When the ICC5 cannot see traffic on this network, the instrument cluster loses its ability to communicate with other ECUs, which is why gauges and steering wheel switches can stop working.
This same SPN/FMI combination also appears tied to the Instrumentation Control Unit, Common (ICUC) in some descriptions, where the symptom is described as the steering wheel switches and gauges not working, confirming the fault is about lost communication on the shared CAN network rather than a single sensor failure.
What triggers a Freightliner SPN639FMI2 code?
The ICC5 sets this fault when battery voltage is within normal operating range, the keyswitch is ON, and the ICC5 is awake, and no messages are received on the chassis CAN. This check runs continuously while those enable conditions are met, with a typical duration of 1.5 seconds before the fault is recorded. On the ICUC-related description, the monitored sequence runs continuously with an execution frequency of 0.1 second.
Common causes of SPN639FMI2
- A wiring problem on the chassis CAN-HIGH or CAN-LOW circuits between the ICC5 (or ICUC) and the rest of the chassis CAN network, including opens, shorts, or damaged pins.
- Incorrect termination resistance on the CAN network, either too high or too low, pointing to a bad terminating resistor or wiring fault at the starpoint connector.
- Loss of supply voltage or ground at the ICC5, checked at pin X1-1 (PWR) and pin X1-6 (GND).
- An active battery voltage fault elsewhere on the truck that should be repaired first, since it can trigger this code as a secondary or nuisance fault.
- A bad connection at the chassis CAN starpoint connector in the Electronics Bay (E-bay).
- A faulty ICC5 module itself, or in the related ICUC description, a faulty ICUC module.
- Corroded, bent, or spread pins at the ICC5 or ICUC connectors.
How to troubleshoot Freightliner SPN639FMI2: first checks
- Turn the keyswitch ON and connect DiagnosticLink. If it communicates successfully with other ECUs on the chassis CAN and no other ECUs report chassis CAN codes, this may be a nuisance code, but repair any active battery voltage faults first.
- Remove the Electronics Bay cover, passenger-side lower dash cover, and Vehicle Power Distribution Module (VPDM) to access the ICC5, then inspect connector pins for bending, spreading, or corrosion.
- Measure supply voltage at the ICC5 between pin X1-1 (PWR) and pin X1-6 (GND) to confirm it is within normal operating range.
- Measure voltage between the battery ground terminal and ICC5 connector X1, pin 13 (chassis CAN-HIGH); it should read between 2.0 and 5.0 volts.
- Measure voltage between the battery ground terminal and ICC5 connector X1, pin 20 (chassis CAN-LOW); it should read between 0.1 and 3.0 volts.
- With the keyswitch OFF and batteries disconnected, backprobe and measure resistance at ICC5 connector X1 between pin 13 (CAN-HIGH) and pin 20 (CAN-LOW), checking for 54 to 66 ohms or, on a second network segment, 36 to 44 ohms.
- Disconnect the chassis CAN starpoint connector in the E-bay and measure resistance on the starpoint side between connector 1 pin 9 (CAN-LOW) and connector C1 pin 7 (CAN-HIGH), checking for 54 to 66 ohms.
- For the ICUC-related version of this symptom, disconnect ICUC connector 1 and inspect for bent or damaged pins, then measure resistance between pins 9 and 18, checking for 54 to 66 ohms.
How the code clears
No separate clearing step is listed beyond fixing the underlying wiring, connector, or module issue. After repairs, reconnect the batteries, turn the keyswitch ON, and connect DiagnosticLink to confirm communication is established with the ICC5 and that fault code SPN 639/FMI 2 is no longer active. If the fault remains active after all wiring and resistance checks pass, the ICC5 (or ICUC, depending on which module is affected) should be replaced. When software is suspected as the cause, a log file with parameters should be pulled and a Daimler Truck Technical Support (DTTS) case opened for further help; the module should only be programmed to the latest or factory record unless directed otherwise.
Frequently asked questions
What does SPN 639 FMI 2 mean on a Freightliner?
It means the Instrument Cluster, Connect 5 (ICC5) module detected a problem with communications on the chassis CAN, specifically that no messages were received on that network while the enable conditions (battery voltage normal, keyswitch ON, ICC5 awake) were met.
Can I still drive with SPN 639 FMI 2 active?
The truck may still drive, but the instrument cluster cannot communicate properly with other ECUs, so gauges and steering wheel switches may stop working. Because you lose visibility into other systems, it is best to diagnose the fault before continuing normal operation.
Is SPN 639 FMI 2 always a real fault or can it be a nuisance code?
It can be a nuisance code. If DiagnosticLink connects successfully to other ECUs on the chassis CAN and none of them report chassis CAN codes, the fault may be a nuisance trigger, but any active battery voltage faults should be repaired first before assuming that.
What voltage and resistance readings should I expect on a good chassis CAN circuit?
At the ICC5, chassis CAN-HIGH should read between 2.0 and 5.0 volts and chassis CAN-LOW should read between 0.1 and 3.0 volts measured to battery ground. Resistance between CAN-HIGH and CAN-LOW should read 54 to 66 ohms, or 36 to 44 ohms depending on the network segment being checked.
What parts need to be removed to access the ICC5 module?
You need to remove the Electronics Bay cover, the passenger-side lower dash cover, and the Vehicle Power Distribution Module (VPDM) to reach the ICC5 connectors.
Does this code affect the ICUC as well as the ICC5?
Yes. A related description ties the same erratic, intermittent, or incorrect data symptom to the Instrumentation Control Unit, Common (ICUC), where the result is that steering wheel switches and gauges do not work. The diagnostic approach is similar, checking connector pins and resistance between two pins on the ICUC connector.
When does the ICC5 or ICUC need to be replaced for this code?
Replacement is called for only after wiring, supply voltage, and CAN resistance checks all come back normal and the fault is still active when reconnecting DiagnosticLink. If a software issue is suspected instead, a log file should be pulled and a Daimler Truck Technical Support case opened before replacing the module.