ABS Modulator Valve Circuit Open
What does VOLVO-MACK-MID136-PID791-FMI5 mean?
The VOLVO-MACK-MID136-PID791-FMI5 (Volvo/Mack D/MP Series) diesel fault code means: ABS Modulator Valve Circuit Open. This is a serious severity code.
Common Symptoms
- ABS warning lamp illuminated
- Possible ATC (traction control) disabled
- ABS disabled during the affected wheel
- Check Engine Light may also set from multiplexing
Probable Causes (Ranked by Likelihood)
- Failed ABS modulator Likely
- Harness damage at wheel end or frame crossover Likely
- Tone ring contaminated with metal debris Possible
- Incorrect sensor air gap from loose mounting Possible
- ABS ECU fault Less Likely
Step-by-Step Diagnostic Procedure
Connect Volvo PTT or Mack Guided Diagnostics (ABS module) and verify MID136-PID791-FMI5 active; read wheel speed live data.
Inspect sensor mounting and air gap; clean tone ring of metallic debris.
Measure sensor resistance at the harness (spec typically 1000-2500 ohms).
Inspect harness routing for chafe at axle flex point and frame crossover.
After repair, road-test above 5 mph to verify fault clears and ABS lamp goes out.
Frequently Asked Questions
What does Volvo/Mack code MID136-PID791-FMI5 mean?
Volvo/Mack code MID136-PID791-FMI5 (ABS Modulator Valve Circuit Open) is a serious-severity diagnostic trouble code set on D11/MP7, D13/MP8, and D16/MP10 diesel engines in Volvo VNL/VNR and Mack Anthem/Pinnacle/Granite/Titan trucks. It indicates a fault in the ABS modulator system and should be read with Volvo Premium Tech Tool (PTT) or Mack Guided Diagnostics.
Can I drive a Volvo or Mack truck with code MID136-PID791-FMI5?
Limited short-term operation is usually possible, but the fault will illuminate the Check Engine Light and should be diagnosed promptly to avoid cascading aftertreatment or fueling faults.
How much does it cost to fix Volvo/Mack code MID136-PID791-FMI5?
Typical repair falls in the range $200-$900. Sensor/wiring repairs are at the low end; EGR cooler, NOx sensor set, DEF pump, injector, or head work runs at the high end. Volvo PTT or Mack Guided Diagnostics is normally required for calibration and parameter programming.