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Semi-Truck ABS Control Module Fault – SPN 807, SPN 611 FMI 14, SPN 792 FMI 5 Explained | UpFix

When the ABS Light Stays On

Your truck’s ABS light comes on, the traction control shuts off, and a quick scan shows wheel speed or communication fault codes. The brakes still work, but you’ve lost your anti-lock and stability protection. This is more than an inconvenience—on wet or icy roads, it’s a safety risk.

If you’ve already replaced sensors or checked wiring, and the faults persist, the issue is likely in the ABS control module (ECU) itself. This small computer regulates braking balance, traction control, and stability assist. When it fails, the system disables itself and logs persistent diagnostic codes.

Common Symptoms

  • ABS light illuminated constantly

  • Traction or ATC (Automatic Traction Control) disabled

  • Brakes lock up under light load

  • Fault codes won’t clear even after replacing sensors

  • Communication errors when scanning the ABS ECU

These issues occur across most commercial trucks including Freightliner, Kenworth, Peterbilt, Volvo, Mack, and International models equipped with Bendix, WABCO, or Meritor WABCO systems.

Typical Fault Codes and What They Mean

Code Description Meaning
SPN 807 FMI 5 Wheel Speed Sensor - Current Below Normal Open circuit or failed channel on ABS ECU
SPN 611 FMI 14 ABS ECU Internal Fault Failed microcontroller or logic board issue
SPN 792 FMI 5 Left Front Wheel Speed Signal Lost Damaged circuit or driver inside module

While wheel sensors themselves can fail, persistent faults that remain after sensor replacement almost always trace back to the ABS ECU.

Why ABS Modules Fail

  1. Thermal fatigue: constant heat cycles from braking cause solder cracks.

  2. Vibration: over-the-road shock damages delicate solder joints.

  3. Moisture intrusion: condensation and road salt corrode circuit boards.

  4. Overvoltage: battery surges or jump-starts burn power supply chips.

  5. Aging components: degraded capacitors lead to weak signal amplification.

When these failures occur, the ECU misreads sensor data or stops communicating with other modules, triggering codes like SPN 611 FMI 14.

The Result: Disabled Safety Systems

When the ABS ECU fails internally, the system shuts down to prevent erratic braking. That means your truck still stops—but without anti-lock modulation, leading to longer stopping distances and potential wheel lock under heavy braking.

How UpFix Repairs ABS ECUs

  1. Module-level diagnostics to verify power, ground, and network integrity.

  2. Replacement of damaged driver transistors and voltage regulators.

  3. Micro-soldering of broken wheel-speed circuit paths.

  4. Reflow of high-vibration solder joints under microscope inspection.

  5. Bench testing with simulated wheel-speed inputs to verify correct response and communication with the ECM.

After repair, the module is resealed and vibration-tested to ensure long-term reliability.

Why Repair Instead of Replace

A new or remanufactured ABS ECU can cost $1,000–$2,000, and sometimes needs dealer configuration or calibration. UpFix repairs your existing unit, retaining its original configuration, VIN data, and calibration settings.

You’ll save:

  • Up to 80% of replacement cost

  • 1–2 days of downtime

  • Environmental waste from discarding functional electronics

Real-World Example

A 2020 Freightliner Cascadia with Bendix EC-60 logged SPN 611 FMI 14 after water intrusion. The ABS light stayed on even after cleaning connectors. UpFix opened the ECU, replaced corroded components, reflowed the CAN transceiver, and resealed the board. The truck passed diagnostic tests on reinstall and the ABS light cleared immediately.

Supported Systems

  • Bendix EC-60 / EC-80 / EC-90

  • WABCO / Meritor WABCO ABS / EBS Systems

  • Freightliner, Volvo, Mack, Kenworth, Peterbilt, International

Why Repairing Is Better for Your Business and the Planet

Every ABS ECU UpFix restores keeps heavy-metal circuit boards and polymer housings out of landfills. Repairing electronics saves over 80% of the energy required to manufacture a new module. For fleets, that translates into lower operating costs and smaller environmental impact.

Get your truck back on the road and keep your costs low.
Send your part to UpFix for professional testing and repair.
We’ll restore it to like-new condition, save you up to 80 percent compared to buying new, and make it plug-and-play ready when returned.