SPN 513 FMI 5: Meaning and Fix
SPN 513 FMI 5 indicates the engine control module (ECM) has detected an open circuit or current below normal on the actual engine percent torque signal circuit. In practice, this fault commonly appears after a wiring harness repair near the exhaust manifold or during a cold start following an engine wash, where moisture ingress causes intermittent open circuit conditions.
Common Symptoms
- Torque Derate: ECM limits engine torque to a default value, typically 30-50%, to protect the powertrain.
- Erratic Idle: Engine hunts or surges at idle due to missing torque feedback for fuel control.
- No Throttle Response: Accelerator pedal input is ignored; engine remains at low idle regardless of demand.
- Diagnostic Lamp On: Red or amber stop engine lamp illuminates immediately on the dash.
Probable Causes
- Open Circuit: Broken wire in the torque signal line between ECM and sensor, often at harness chafe points.
- Corroded Connector: Pin corrosion at the ECM 120-pin connector, especially pin 53 on Bosch EDC7 units.
- Sensor Failure: Internal open circuit within the torque sensor module, common on Deutz TCD 2013 engines.
- ECM Fault: Damaged ECM input driver stage due to voltage spike or short to battery.
Advanced Technical Analysis
The ECM monitors the torque signal via an analog-to-digital converter on a dedicated input pin. A debouncing timer of 200 ms must elapse with the signal below 0.5 mA before the fault is logged. This prevents false triggers from transient noise during starter engagement.
The torque sensor operates as a current sink, outputting 4-20 mA proportional to 0-100% torque. An open circuit forces the input voltage to pull-up level (5V). The ECM interprets this as current below normal and sets FMI 5. Resistance to ground should be less than 10 ohms.
Upon detecting FMI 5, the ECM activates a torque derate strategy using a default torque map based on engine speed and coolant temperature. This fallback prevents runaway but reduces power by up to 60%. The derate remains active until the fault is cleared and a key cycle is performed.
Long-term prevention includes dielectric grease application on all torque circuit connectors and periodic inspection of harness routing near heat sources. In workshops, this fault is often resolved by replacing the engine harness section between the ECM and the intake manifold on MAN D26 engines.
Step-by-Step Troubleshooting Guide
- Visual Inspection: Check harness for chafing or burns near exhaust, especially at the rear of the cylinder head.
- Resistance Test: Measure resistance between ECM pin and sensor pin; should be below 2 ohms. Open indicates break.
- Connector Check: Disconnect ECM and sensor connectors; inspect for bent, corroded, or pushed-back pins.
- ECM Replacement: If all wiring and sensor tests pass, replace ECM and reprogram using factory scan tool.