SPN 625 FMI 11: Meaning and Fix
SPN 625 FMI 11 triggers when the Stop Start Broadcast message from the proprietary network #1 is received with an undefined failure mode. In practice, this code commonly appears after a forced DPF regeneration where the ECM loses synchronization with the stop-start controller, leaving the root cause unlogged. Technicians frequently encounter this fault after replacing the ECM without proper parameter transfer, as the new controller cannot interpret the legacy broadcast format.
Common Symptoms
- Erratic Stop-Start: Engine fails to shut down or restart predictably during stop-start cycles, causing driver complaints.
- No Fault Lamp: MIL or amber warning lamp may not illuminate despite active code, delaying diagnosis.
- Intermittent Idle: Engine idle speed fluctuates or remains elevated when stop-start is commanded active.
- Communication Loss: Secondary controllers, such as AC or alternator, report missing stop-start broadcast data.
Probable Causes
- Corrupted Parameter: Stop-start enable parameter in ECM is set to an unsupported value per J1939-73 annex.
- ECM Flash Error: Incomplete or mismatched firmware update leaves the broadcast message undefined.
- Wiring Harness Fault: Intermittent short or open on proprietary network #1 CAN lines corrupts message integrity.
- Battery Voltage Drop: Low system voltage during crank causes ECM to log unknown failure state in broadcast.
Advanced Technical Analysis
The ECM microcontroller monitors the Stop Start Broadcast (PGN 0x00FEE9) on proprietary network #1. When the message is received but the failure mode identifier (FMI) byte is set to 11 (0x0B), the software cannot map it to any known diagnostic trouble code. This typically occurs when the transmitting controller uses a non-standard failure mode byte, often due to a corrupted calibration table in the stop-start module.
Electrical analysis reveals that the proprietary network #1 lines (CAN_H and CAN_L) operate at 250 kbps with a nominal 2.5V differential. A debouncing timer of 500 ms is used to filter transient glitches. If the FMI byte remains at 11 for more than three consecutive messages, the ECM latches the fault. This can happen when a voltage spike on the CAN bus flips the FMI byte to an undefined value.
Upon detecting SPN 625 FMI 11, the ECM enters a safety fallback mode that disables the stop-start function entirely. A torque derate of 10% is applied to prevent unexpected engine shutdowns. The proprietary network #1 is isolated from the primary J1939 backbone via a gateway, ensuring that other critical messages (e.g., EEC1) remain unaffected. This behavior is documented in Bosch EDC17 ECU application notes.
Long-term diagnostic strategy involves cross-referencing the stop-start module’s internal fault log using manufacturer-specific diagnostic tools (e.g., MAN CATS or Deutz EMR). In one real workshop scenario, a technician resolved this fault by performing a forced parameter reset via the OEM’s proprietary software after a battery replacement. Prevention includes verifying that all controllers share the same software version after any reflash event.
Step-by-Step Troubleshooting Guide
- Check CAN Bus: Measure resistance between CAN_H and CAN_L at the stop-start module; expect 60 ohms.
- Verify Parameters: Read stop-start enable parameter using OEM tool; set to factory default if corrupted.
- Update Firmware: Re-flash ECM and stop-start controller with latest manufacturer-approved calibration files.
- Inspect Grounds: Check chassis ground connections at battery and ECM; clean and tighten if voltage drop exceeds 0.2V.