Cummins · Driver's Demand Engine Percent TorqueMedium

Cummins SPN 512 FMI 2: Diagnosing Erratic Driver's Demand Torque

SPN 512 FMI 2 (FMI 2) — Driver's Demand Engine - Percent Torque - Data Erratic, Intermittent, Or Incorrect

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Quick Answer

SPN 512 FMI 2 on Cummins engines means the calculated driver's demand torque signal is erratic or inconsistent. It's a medium-severity fault that usually traces back to the accelerator pedal position sensor or its wiring rather than a standalone software issue.

Overview: Cummins SPN 512 FMI 2

Driver's demand percent torque is the ECM's translation of accelerator pedal input into a torque request, so when SPN 512 FMI 2 shows this value as erratic, the root cause is almost always upstream at the pedal assembly. ProfessionalDieselRepair.com sees this fault produce inconsistent throttle response that can be frustrating to pin down if you don't start at the pedal sensor first, since the fault code itself doesn't explicitly point there.

Repair Snapshot

Time

1 - 3 Hours

Difficulty

Intermediate

Parts Cost

$50 - $300

Dealer Labor

$350+

Tools Required

  • Cummins INSITE
  • Multimeter
  • Diesel Laptops Scan Tool
  • Contact Cleaner

What SPN 512 FMI 2 Means

SPN 512 FMI 2 means the ECM is seeing erratic or inconsistent data for driver's demand torque - essentially the translated accelerator pedal request. On Cummins ISX/X15 engines this is a medium-severity fault that can cause hesitation or surging because the ECM can't trust the torque request it's receiving, even though it's not a direct sensor circuit fault like a low or high voltage code.

Symptoms Drivers Notice

  • Surging or hesitation under acceleration
  • Inconsistent throttle response, sometimes normal and sometimes sluggish
  • Amber Check Engine lamp
  • Occasional unexpected power reduction without a clear pattern

Most Likely Root Causes

Faulty or worn accelerator pedal position sensor

Common

Wear inside the dual-track pedal sensor can cause one or both signal tracks to jump or drop out intermittently, producing erratic torque demand data.

Chafed or corroded pedal harness wiring

Common

The pedal harness flexes with every use, making it prone to wear and intermittent connection issues over time.

Loose or partially backed-out ECM connector pin

Occasional

A pin that isn't fully seated can create an intermittent connection that produces erratic data without a clean fault pattern.

J1939 network communication interference

Rare

Data corruption on the CAN bus between modules can occasionally produce erratic readings for shared parameters like torque demand.

Common Misdiagnoses (Don't Waste Parts)

Replacing the ECM for an erratic data fault

Why it happens: Erratic or 'incorrect' data faults sound like a control module problem, tempting some techs toward the most expensive parts-cannon swap available.

Do this instead: Check the accelerator pedal sensor and its harness thoroughly first - this is overwhelmingly the more common and far cheaper root cause.

Overlooking the pedal harness because the pedal 'feels normal' to the driver

Why it happens: Intermittent electrical faults don't always produce a consistent physical symptom the driver notices.

Do this instead: Test the pedal sensor's signal output through its full range of motion with a multimeter, watching for any jumps or dropouts rather than relying on driver feedback alone.

Master Tech Commentary

Mechanic's Notes

Shop tip: this code almost always traces back to the accelerator pedal position sensor or its harness, even though the fault text doesn't mention the pedal directly. ProfessionalDieselRepair.com always starts at the pedal assembly on this one rather than chasing it as a standalone ECM software issue.

Step-by-Step Diagnostic Procedure

  1. Step 1: Pull the fault with Cummins INSITE and confirm SPN 512 FMI 2 is active; check whether it correlates with accelerator pedal position sensor faults (SPN 91) logged around the same time.
  2. Step 2: Inspect the accelerator pedal assembly and its wiring harness for looseness, water intrusion, or a chafed wire - the pedal sensor is the primary source feeding this calculated value.
  3. Step 3: Check the pedal sensor's dual-track signal outputs with a multimeter while slowly depressing the pedal - both tracks should move smoothly and proportionally without jumps or dropouts.
  4. Step 4: Verify ECM connector pins for the pedal circuit are clean and fully seated - a partially backed-out pin can cause exactly this kind of erratic data pattern.
  5. Step 5: If the pedal assembly and wiring check out, use INSITE to check for any J1939 network communication errors between the ECM and other modules that share this torque-demand data.
  6. Step 6: Clear the code and road test through varying throttle inputs to confirm smooth, consistent torque demand tracking before returning the truck to service.

Live Data & Freeze-Frame Tips

Graph both accelerator pedal position and driver's demand torque simultaneously on INSITE while slowly and smoothly depressing the pedal through its full range. Any dropout, spike, or mismatch between the two signals pinpoints exactly where in the chain the erratic data originates.

Safety Warnings

  • Disconnect the battery before repairing any wiring near the pedal assembly to avoid unintended engine response during testing.
  • Test the pedal circuit with the parking brake set and wheels blocked if any live engine testing is required.

When to Limp In vs Tow

Towing is rarely necessary for this fault, but if surging or unexpected power loss becomes severe enough to be unsafe in traffic, have the truck inspected before continuing to drive.

Prevention Tips for Fleets & Owner-Operators

  • Inspect the accelerator pedal harness for wear at every major PM interval.
  • Keep the pedal assembly connector clean and free of moisture intrusion.
  • Avoid aftermarket pedal assemblies not designed to the OEM dual-track specification.

Related Fault Codes

SPN 91 FMI 2

Accelerator pedal position sensor data erratic - the most likely underlying source of an erratic torque demand reading.

SPN 513 FMI 2

Actual engine percent torque data erratic - a related torque parameter that can show similar symptoms from a different cause.

SPN 91 FMI 13

Accelerator pedal position sensor out of calibration - a distinct fault that can also disrupt torque demand accuracy.

Frequently Asked Questions

Can I drive with SPN 512 FMI 2 active?

Yes, though expect inconsistent throttle response. It's worth diagnosing soon since surging can be unpredictable and mildly unsafe in heavy traffic.

Does this code mean my accelerator pedal is bad?

Often yes, or at least the pedal's wiring - this is the most common root cause even though the fault code itself references calculated torque demand rather than the pedal directly.

How do I reset SPN 512 FMI 2 without a scan tool?

You need Cummins INSITE or a comparable tool to clear the stored fault after the pedal sensor or wiring issue is resolved.

Will this code cause an engine derate?

Not directly in most cases - it primarily causes inconsistent throttle response rather than triggering the ECM's protective derate logic.

Is this an expensive repair?

Usually not - it's most often resolved with a pedal sensor replacement or a wiring repair, both relatively affordable compared to a control module issue.

Can a software update fix this code?

Rarely - this is almost always a hardware issue at the pedal sensor or its harness rather than something an ECM reflash would resolve.