Detroit Diesel · Actual Engine Percent TorqueMedium

Detroit Diesel SPN 513 FMI 2: Diagnosing Erratic Actual Engine Torque

SPN 513 FMI 2 (FMI 2) — Actual Engine - Percent Torque - Data Erratic, Intermittent, Or Incorrect

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Quick Answer

SPN 513 FMI 2 on Detroit DD13/DD15 engines means the ECM's calculated actual torque output is erratic. It's a medium-severity fault caused by inconsistency in one of the underlying inputs - typically engine speed or fuel rate - rather than a dedicated torque sensor.

Overview: Detroit Diesel SPN 513 FMI 2

Actual engine percent torque isn't measured by a single sensor - it's calculated from engine speed, fuel rate, and rail pressure data. That means SPN 513 FMI 2 is really a symptom pointing back to one of those upstream inputs rather than a standalone fault to chase directly. ProfessionalDieselRepair.com works this one systematically, checking the engine speed sensor and fuel rate stability before assuming anything deeper is wrong, since those two inputs cause the overwhelming majority of erratic torque calculation faults.

Repair Snapshot

Time

1.5 - 4 Hours

Difficulty

Advanced

Parts Cost

$60 - $500

Dealer Labor

$450+

Tools Required

  • Detroit Diesel Diagnostic Link (DDDL)
  • Multimeter
  • Snap-on NEXIQ Adapter
  • Diesel Laptops Scan Tool

What SPN 513 FMI 2 Means

SPN 513 FMI 2 means the ECM's calculated actual engine torque output value is erratic or inconsistent. On a DD13/DD15, this is a medium-severity fault - it's a calculated parameter derived from multiple sensor inputs including fuel rate and RPM, so an erratic reading here often points to a problem with one of those underlying inputs rather than a single dedicated sensor.

Symptoms Drivers Notice

  • Inconsistent power delivery that's hard for the driver to describe precisely
  • Amber Check Engine lamp
  • Torque values that jump or spike unexpectedly on the scan tool's live data screen
  • Possible interaction with transmission shift quality on automated manual transmissions that use torque data for shift timing

Most Likely Root Causes

Erratic engine speed sensor signal

Common

Since RPM is a core input to the torque calculation, an intermittent or noisy speed sensor signal directly corrupts the resulting torque value.

Unstable fuel rate or rail pressure sensor data

Common

Fuel rate and rail pressure feed the torque calculation; inconsistency in either input produces the same erratic torque symptom.

Loose or corroded ECM connector pins on input circuits

Occasional

A poor connection on any contributing sensor circuit can introduce noise that shows up as erratic calculated torque rather than a clean sensor fault.

J1939 network data corruption between modules

Rare

If torque data is shared across the network with a transmission or other module, communication errors can occasionally produce erratic readings without a physical sensor fault.

Common Misdiagnoses (Don't Waste Parts)

Searching for a dedicated 'torque sensor' to replace

Why it happens: Techs unfamiliar with how this parameter is derived assume there's a physical sensor for it, leading to a wasted parts search or an unnecessary parts-cannon purchase of the wrong component.

Do this instead: Recognize that this is a calculated value and diagnose the actual contributing sensors - engine speed and fuel rate - instead.

Replacing the ECM for an erratic calculation fault

Why it happens: When no single sensor jumps out as clearly faulty, some techs escalate straight to the control module.

Do this instead: Thoroughly rule out engine speed sensor and fuel rate/rail pressure sensor issues, plus connector integrity, before ever considering ECM replacement.

Master Tech Commentary

Mechanic's Notes

Shop tip: because this is a calculated value, don't waste time looking for a 'torque sensor' that doesn't exist. ProfessionalDieselRepair.com works this fault by checking every input that feeds the calculation - engine speed, fuel rate, and rail pressure - rather than treating it as a single-component repair.

Step-by-Step Diagnostic Procedure

  1. Step 1: Pull the fault with DDDL and confirm SPN 513 FMI 2 is active; check for any accompanying faults on fuel rate (SPN 183), engine speed (SPN 190), or rail pressure sensors that feed the torque calculation.
  2. Step 2: Inspect the engine speed sensor and its wiring for looseness or damage, since an erratic RPM signal directly corrupts the torque calculation.
  3. Step 3: Check fuel rail pressure sensor readings for stability using DDDL live data - an erratic pressure signal will similarly throw off the calculated torque value.
  4. Step 4: Verify all ECM connector pins related to these input sensors are clean, dry, and fully seated.
  5. Step 5: If a transmission is present that shares this data over the J1939 network, check for any network communication fault codes that might indicate a broader data integrity issue rather than a single sensor.
  6. Step 6: Clear the code and road test while monitoring live torque data for stability across varying loads before returning the truck to service.

Professional service / OEM-level scan tools are recommended before clearing this fault for good.

Live Data & Freeze-Frame Tips

On DDDL, log engine speed, fuel rate, rail pressure, and calculated torque together on the same timeline. Whichever input shows a spike or dropout at the same moment the torque value glitches is your root cause - this side-by-side comparison is far faster than testing each sensor individually.

Safety Warnings

  • Use proper lockout procedures before working on any rotating components near the engine speed sensor.
  • Disconnect the battery before repairing wiring near the crankshaft or camshaft sensor area.

When to Limp In vs Tow

Towing generally isn't required for this fault by itself, but if it's paired with an automated transmission shifting harshly or unpredictably due to bad torque data, have the truck inspected before a long trip.

Prevention Tips for Fleets & Owner-Operators

  • Inspect the engine speed sensor and its wiring at every major PM interval.
  • Keep fuel system components maintained to avoid rail pressure instability that can cascade into torque calculation faults.
  • Address any connector corrosion on input sensor circuits promptly.

Related Fault Codes

SPN 190 FMI 8

Engine speed abnormal frequency - a likely underlying cause if the RPM signal is corrupting the torque calculation.

SPN 512 FMI 2

Driver's demand torque data erratic - a related but distinct torque parameter that stems from the pedal input rather than engine output calculations.

SPN 183 FMI 2

Engine fuel rate erratic - another key input to the actual torque calculation that can produce this same downstream symptom.

Frequently Asked Questions

Can I drive with SPN 513 FMI 2 active?

Yes, though expect inconsistent power delivery. If the truck has an automated transmission, shift quality may also be affected since some AMTs use torque data for shift timing.

Is there a dedicated torque sensor I need to replace?

No - actual engine torque is a calculated value derived from engine speed, fuel rate, and rail pressure data, not measured by a single physical sensor.

How do I reset SPN 513 FMI 2 without a scan tool?

You need DDDL or a comparable diagnostic tool to clear the stored fault once the underlying sensor input causing the erratic calculation is repaired.

Will this code cause an engine derate?

Not typically on its own - it's more likely to cause inconsistent power feel or shift quality issues than trigger a hard protective derate.

What's the most likely cause of this specific fault?

An erratic engine speed sensor signal or unstable fuel rate/rail pressure data are the two most common root causes, since both feed directly into the torque calculation.

Does this fault affect automated transmission shifting?

It can, if the transmission control module relies on torque data over the J1939 network for shift timing - erratic torque values may cause harsh or unpredictable shifts.