SPN 147 FMI 13: Meaning and Fix
SPN 147 FMI 13 indicates the Engine Average Fuel Economy (gaseous) sensor or calculation is out of calibration. This code commonly appears after a forced DPF regeneration or after replacing the ECM, when the fuel economy offset values have not been rewritten. Technicians often encounter this fault when a new calibration file is flashed without resetting the fuel economy learning parameters, leading to implausible data on the J1939 data link.
Common Symptoms
- Incorrect Fuel Readings: Dash displays implausible fuel economy values, often showing zero or maximum scale during steady-state operation.
- Check Engine Light: MIL or amber warning lamp activates immediately after key-on with no drivability issues present.
- No Power Derate: Engine operates normally without torque limitation, as this fault is informational for gaseous fuel systems.
- Diagnostic Trouble Code: Active or inactive SPN 147 FMI 13 stored in ECM memory, retrievable via J1939 scan tool.
Probable Causes
- ECM Calibration Mismatch: Incorrect or incomplete calibration file loaded after ECM replacement or software update.
- Fuel Sensor Offset Error: Gaseous fuel flow sensor zero-point drift or incorrect gain factor causing out-of-range calculation.
- Parameter Reset Required: Fuel economy learning values not reset after DPF regeneration or battery disconnect.
- Corrupted Data Link: J1939 CAN bus noise or intermittent connection corrupting fuel economy parameter transmission.
Advanced Technical Analysis
The ECM calculates average fuel economy by integrating fuel mass flow from the gaseous fuel sensor against vehicle speed over time. FMI 13 triggers when the calculated value deviates beyond a tolerance band (typically ±15%) from a factory-stored reference model. This is a soft fault; the ECM continues normal operation but flags the calibration mismatch for service.
Electrical analysis reveals that the fuel flow sensor signal is processed through an analog-to-digital converter with a 10-bit resolution. The ECM applies a calibration coefficient stored in non-volatile memory. If this coefficient is corrupted or written incorrectly, the resulting fuel economy value falls outside the plausibility window, setting FMI 13 without a hardware short or open circuit.
Safety fallback mechanisms are minimal for this informational parameter. The ECM does not initiate torque derate or limp-home mode. Instead, it substitutes a default fuel economy value (e.g., 0.0 km/kg) for display purposes. This prevents false warnings to the operator while the fault remains flagged for diagnostic retrieval.
Long-term prevention requires verifying that the correct calibration file (e.g., Bosch EDC17 or Deutz EMR4) is loaded after any ECM reprogramming. Real-world workshop example: after replacing an ECM on a MAN TGS with a CNG engine, technicians must perform a ‘fuel economy reset’ via manufacturer software (e.g., MAN Cats II) to clear SPN 147 FMI 13.
Step-by-Step Troubleshooting Guide
- Verify Calibration: Check ECM part number and calibration file version against manufacturer specifications using J1939 tool.
- Reset Fuel Economy: Perform a fuel economy learning reset via diagnostic software to clear stored offset values.
- Inspect CAN Bus: Measure termination resistance (60 ohms) and check for voltage drops on J1939 high/low lines.
- Test Fuel Sensor: Monitor live fuel flow data at idle and rated speed; compare to factory reference values.