SPN 6713 FMI 20: Meaning and Fix
SPN 6713 FMI 20 indicates the software identification parameter from the variable geometry turbocharger actuator has drifted above the expected range. This code commonly appears after an ECM software update or actuator replacement when the component’s internal firmware version does not match the ECM’s calibration table. Technicians frequently encounter this fault after swapping a VGT actuator from a different engine model without reflashing the correct software.
Common Symptoms
- Engine Derate: ECM reduces torque by up to 40% to protect turbocharger from overspeed or incorrect vane position.
- Diagnostic Lamp: Amber warning lamp illuminates immediately; red stop lamp may activate if boost pressure exceeds limits.
- Poor Acceleration: Turbocharger fails to modulate vane angle, causing sluggish response and black smoke under load.
- Fault Code Stored: SPN 6713 FMI 20 is logged as active or inactive; may be accompanied by SPN 102 FMI 0.
Probable Causes
- Software Mismatch: Actuator firmware version differs from ECM calibration, causing data drift beyond 5% tolerance.
- Corrupted Actuator: Internal memory corruption from voltage spikes or failed flash update during programming.
- ECM Calibration Error: Incorrect part number entered during ECM replacement or reflash via diagnostic tool.
- Wiring Harness Issue: High resistance on CAN bus lines (J1939) distorts software ID transmission, simulating drift.
Advanced Technical Analysis
The ECM monitors the VGT actuator’s software identification via a proprietary J1939 diagnostic message (PGN 65251). When the received ID exceeds the stored reference by more than 2% of the expected value, the ECM sets FMI 20. This threshold is defined in Bosch EDC17 calibration maps and is not user-adjustable. The fault triggers a debouncing timer of 5 seconds to prevent false positives from transient noise.
Electrical analysis reveals that a 0.5V drop on the actuator’s power supply line (typically 24V nominal) can corrupt the internal flash memory readout, causing the software ID to drift high. Mercedes-Benz factory manuals specify checking supply voltage at the actuator connector under load (minimum 22.5V). Any deviation below this threshold mandates repair of the power harness before replacing components.
Upon detecting data drifted high, the ECM activates a safety fallback that locks the VGT vanes at a predetermined position (usually 60% open). This reduces boost pressure by approximately 30% and limits engine torque to 60% of rated value. The fallback remains active until the fault is cleared via a diagnostic tool and a successful actuator self-test is completed.
Long-term prevention requires verifying actuator software compatibility using OEM tooling (e.g., MAN CATS or Deutz EMR). A real-world example: a fleet of Mercedes-Benz OM471 engines repeatedly triggered SPN 6713 FMI 20 after field actuator swaps. The root cause was using actuators programmed for OM470 engines. Flashing the correct software via XENTRY resolved all cases permanently.
Step-by-Step Troubleshooting Guide
- Read Software ID: Use diagnostic tool to read actuator software ID; compare with ECM calibration list for exact match.
- Check Supply Voltage: Measure voltage at actuator pin 1 (24V) and pin 2 (ground) under key-on; must be 22.5-28V.
- Inspect CAN Bus: Check resistance between CAN H and CAN L at actuator connector; should be 60 ohms with terminations.
- Reprogram Actuator: Flash correct firmware using OEM tool; perform actuator calibration and clear fault code.