SPN 807 FMI 9: Meaning and Fix
SPN 807 FMI 9 indicates the Differential 2 ASR valve is transmitting at an abnormal update rate on the J1939 CAN bus. The ECM expects a periodic message every 50 ms; deviation triggers this fault. Technicians often see this after a valve replacement when the harness connector is not fully seated, causing intermittent contact and timing jitter. A real-world example is a wheel loader that lost traction control after a DPF regeneration due to heat-induced connector expansion.
Common Symptoms
- Traction Control Loss: ASR system deactivates differential braking, causing wheel spin on low-grip surfaces during acceleration.
- Dashboard Warning Lamp: Amber ASR or ABS warning illuminates continuously; no flashing during self-test at key-on.
- Erratic Brake Modulation: Intermittent pulsing in brake pedal feel during low-speed maneuvers, especially on uneven terrain.
- CAN Bus Errors: J1939 passive error frames increase; scan tool shows intermittent loss of message ID 0xCF00400.
Probable Causes
- CAN Bus Wiring Fault: Open or high-resistance in CAN_H or CAN_L lines between valve and ECM, causing message timing drift.
- Valve Internal Failure: Microcontroller clock drift or voltage regulator instability inside the ASR valve solenoid assembly.
- ECM Software Mismatch: Incorrect calibration ID loaded after ECM replacement; expected update rate differs from actual valve response.
- Connector Corrosion: Moisture ingress at Deutsch DT04-2P connector pins increases contact resistance, delaying signal edges.
Advanced Technical Analysis
The ECM monitors the ASR valve message ID 0xCF00400 using a 50 ms reception window. If the time between consecutive messages exceeds 65 ms or falls below 35 ms for three cycles, the FMI 9 is set. The J1939 data link layer uses a 250 kbps bit rate; any noise or termination mismatch can shift the message arrival time outside the debouncing window.
Electrically, the valve solenoid driver relies on a 12 V supply with a 100 mV ripple tolerance. If the supply voltage drops below 10.5 V during engine cranking, the valve microcontroller resets, causing a missed transmission. The ECM detects this as an abnormal update rate and logs SPN 807 FMI 9. A scope capture often shows a 20 ms pause in the CAN trace.
Upon fault activation, the ECM enters a safe mode: it sets the ASR valve to a default closed position and disables differential braking. The engine torque is derated by 30% in off-highway gears to prevent loss of control. This fallback remains active until the fault is cleared and the ignition is cycled, even if the CAN message resumes.
Long-term prevention requires verifying the valve firmware version matches the ECM calibration. In a Deutz TCD 6.1 engine application, technicians found that replacing the valve without updating the ECM caused persistent FMI 9 faults. A permanent fix involved flashing both units with the same release date. Always check for TSBs regarding CAN bus termination resistor values (120 Ω ± 10%).
Step-by-Step Troubleshooting Guide
- Verify CAN Termination: Measure resistance between CAN_H and CAN_L at the valve connector; must be 60 Ω with bus powered off.
- Inspect Connector Pins: Remove Deutsch DT04-2P; check for bent, corroded, or pushed-back pins. Clean with contact cleaner.
- Monitor Message Timing: Use oscilloscope on CAN bus; capture ID 0xCF00400 and measure inter-message gap. Expect 50 ms ± 5 ms.
- Check Supply Voltage: Measure voltage at valve pin 1 during engine idle; must be 12.0 V ± 0.5 V with less than 50 mV AC ripple.