SPN 1328 FMI 19: Meaning and Fix
SPN 1328 FMI 19 indicates the Engine Control Module (ECM) received invalid or erroneous data regarding the cylinder 6 misfire rate, calculated as a percentage over engine cycles. This is a network data error, not a direct mechanical misfire detection. In practice, this code commonly appears after a forced DPF regeneration, where electrical noise or voltage spikes corrupt the CAN message from the cylinder contribution module.
Common Symptoms
- Reduced Engine Power: ECM enters a torque derate strategy to protect the aftertreatment system, limiting vehicle drivability.
- Illuminated MIL Lamp: The malfunction indicator lamp on the dashboard illuminates, prompting the driver to seek immediate service.
- Rough Idle Complaint: Although data is faulty, the engine may exhibit a slight roughness if the underlying cause also affects combustion.
- Data Link Failure: Proprietary diagnostic tools may fail to display live cylinder 6 contribution values due to the corrupted data stream.
Probable Causes
- CAN Bus Corruption: Shorted or open wiring in the J1939 data link, causing intermittent or corrupted signal transmission from the engine.
- ECM Software Bug: Outdated or corrupt firmware in the engine control module, leading to improper calculation or interpretation of misfire data.
- Faulty Injector Harness: Chafed or damaged wiring harness near cylinder 6, inducing electromagnetic interference into the signal lines.
- Sensor Ground Shift: A poor ground connection for the cylinder 6 combustion sensor, causing voltage offset and data misinterpretation.
Advanced Technical Analysis
The ECM’s microcontroller monitors the crankshaft acceleration via the 60-2 tooth wheel and calculates individual cylinder contribution. For the misfire rate, it compares the instantaneous angular velocity against a learned baseline. FMI 19 triggers when the received data packet on the internal CAN bus, which carries the cylinder 6 rate from a secondary processor, fails a checksum or cyclic redundancy check (CRC). This points to a communication failure rather than a physical misfire event.
Electrical breakdown typically involves a debouncing timer. The ECM requires the error to be present for a specific number of consecutive messages, usually 5 to 10, before setting the code. A single glitch due to a relay closing is ignored. However, if the wiring harness has a high resistance connection, the CAN transceiver may see a dominant bit error, leading to a bus-off condition, which immediately sets this diagnostic.
The safety fallback mechanism is a two-stage derate. First, the ECM limits maximum engine speed to 1700 RPM. Second, it reduces maximum torque by 50% if the error persists for more than 30 seconds. This prevents the driver from operating the vehicle under unknown combustion conditions, which could lead to catalytic converter damage from unburned fuel.
Long-term prevention requires checking the ECM connector for corrosion, specifically pins related to the cylinder 6 injector return line. In a real workshop case on a Deutz TCD 7.0, this code appeared after a valve adjustment. The technician had accidentally pinched the wiring harness under the valve cover, causing a short. Repairing the harness and clearing the code resolved the issue permanently.
Step-by-Step Troubleshooting Guide
- Scan Data Check: Use a diagnostic tool to compare SPN 1328 value against SPN 6394 (engine cycles). A value of 0% with an error indicates data link issue.
- Inspect Harness: Physically inspect the J1939 backbone and the cylinder 6 injector harness for chafing, corrosion, or loose connectors.
- Verify CAN Terminations: Measure resistance between CAN_H and CAN_L at the ECM connector. Must read 60 ohms with power off, indicating proper termination.
- Update ECM Firmware: Check the manufacturer’s service portal for a flash update. Many early production runs have known communication stack bugs fixed by new software.