SPN 807 FMI 5: Meaning and Fix
This fault code indicates the ECM detected an open circuit or current below the normal threshold on the secondary ASR (Automatic Slip Regulation) valve solenoid circuit. In practice, this commonly appears after a wiring harness repair near the rear axle or following a valve replacement where the connector was not fully seated. A technician may also encounter this after a chassis wash, when moisture enters the valve connector.
Common Symptoms
- Traction Control Inactive: ASR system disables, allowing wheel slip under acceleration on low-friction surfaces.
- Dashboard Warning Light: Amber ASR or traction control lamp remains illuminated continuously during engine operation.
- No Diagnostic Response: J1939 data link reports no current flow on ASR valve circuit during actuator test.
- Intermittent Fault Recall: Fault may log as active during key-on but self-clear if circuit briefly reconnects.
Probable Causes
- Open Wiring Harness: Broken conductor between ECM pin and ASR valve solenoid connector, often near chassis flex points.
- Corroded Connector Terminals: Oxidation on Deutsch or AMP pins increases resistance, dropping current below threshold.
- Failed Solenoid Coil: Internal winding open circuit due to thermal stress or mechanical vibration over time.
- ECM Output Driver Failure: Internal MOSFET or flyback diode shorted open, preventing current flow to the solenoid.
Advanced Technical Analysis
The ECM continuously monitors the ASR valve solenoid circuit using a low-side driver with current sensing. When the ignition is on, a 200 ms diagnostic pulse is sent; if the sensed current remains below 50 mA for 3 consecutive cycles, the fault is set. The driver expects a nominal load of 1.2-1.5 A at 12 V. An open circuit yields near-zero current, triggering FMI 5.
Electrical analysis requires verifying continuity from ECM pin J1-xx to the solenoid. A digital multimeter should show 4-6 ohms across the coil at 20°C. If reading is OL, the solenoid is open. A debouncing timer of 0.5 seconds prevents false positives from transient vibrations. Real-world: a chafed wire near the frame crossmember is a frequent root cause.
Upon detecting this fault, the ECM disables ASR functionality and stores the code as active. The vehicle may experience a slight torque reduction if the ASR system is integrated with the engine ECU via J1939. No limp-home mode is triggered, but wheel slip control is lost. Technicians should note that this code often appears alongside SPN 806 FMI 5 if both valves are affected.
Long-term prevention includes using dielectric grease on connectors and routing harnesses away from heat sources. In one workshop scenario, a technician traced this fault to a pin pushed back inside the ECM 70-pin connector after a previous repair. Releasing the terminal lock and reseating the pin restored circuit integrity. Always perform a wiggle test on the harness with the multimeter connected.
Step-by-Step Troubleshooting Guide
- Visual Inspection: Check ASR valve connector for bent pins, corrosion, or moisture ingress near the rear axle.
- Solenoid Resistance Test: Measure across solenoid terminals; should read 4-6 ohms. Open indicates coil failure.
- Circuit Continuity Check: Disconnect ECM and valve; verify continuity from ECM pin to solenoid connector with no shorts to ground.
- ECM Driver Test: Reconnect solenoid, use diagnostic tool to command valve on; confirm current draw of 1.2-1.5 A.