Do not driveMinutes
J1939 code SPN 791. Below — how the fault is worded at the factory by Bendix ABS/ESP, Knorr-Bremse EBS, MAN, Meritor (ex-WABCO), Renault Trucks, SITRAK and WABCO ABS/ESC, and what the second half of the code (FMI) means in the standard.
Bendix ABS/ESPKnorr-Bremse EBSMANMeritor (ex-WABCO)Renault TrucksSITRAKWABCO ABS/ESC
| FMI 1 | DA Left WSS Excessive Air Gap |
| FMI 2 | DA Left WSS Open or Shorted |
| FMI 7 | DA Left WSS Wheel End |
| FMI 8 | DA Left WSS Erratic Sensor Signal |
| FMI 10 | DA Left WSS Loss of Sensor Signal |
| FMI 13 | DA Left WSS Tire Size Calibration |
| FMI 14 | DA Left WSS Output Low @ Drive-Off |
| FMI 4 | Sensor wheel speed, wheel 3. No signal |
| FMI 7 | Sensor wheel speed, wheel 3. Short |
| FMI 4 | Sensor wheel speed wheel 3 - No signal |
| FMI 7 | Sensor wheel speed wheel 3 - Closing |
| FMI 1 | AirGap Failure of Wheel Speed Sensor (Drive Axle Left) |
| FMI 3 | Short Circuit to UB of Wheel Speed Sensor (Drive Axle Left) |
| FMI 4 | Short Circuit to GND of Wheel Speed Sensor (Drive Axle Left) |
| FMI 5 | Interruption of Wheel Speed Sensor (Drive Axle Left) |
| FMI 7 | Wheel Speed Sensor (Drive Axle Left) |
| FMI 11 | Plausibility Check of Wheel Speed Sensor (Drive Axle Left) |
| FMI 13 | Failure Detection 'OverEquipped' of Wheel Speed Sensor (Drive Axle Left) |
| FMI 14 | RunOut Failure of Wheel Speed Sensor (Drive Axle Left) |
| FMI 1 | Rear left wheel speed sensor — air gap too large. Repair: Check the sensor air gap. |
| FMI 2 | Rear left wheel speed sensor — open or short circuit. Repair: Check the sensor resistance (950-1930 ohms). Check the continuity of the speed sensor wiring (X4/5, X4/6). |
| FMI 7 | Rear left wheel speed sensor — large air gap or damaged tone wheel. Repair: Check the sensor air gap. Check the sensor air gap. Check the toothed wheel for tooth condition and axial run-out. |
| FMI 8 | Rear left wheel speed sensor — signal lost while driving or implausible, ABS control disturbed. Repair: Check the sensor air gap and the toothed wheel. If the fault persists, replace the speed sensor. Check the sensor resistance (950-1930 ohms). Check the toothed wheel for tooth condition and axial run-out. Check that there is no residual pressure in the brake chambers. Check the brake mechanisms for mechanical binding. |
| FMI 10 | Rear left wheel — ABS control fault or tone wheel defect. Repair: Check the sensor resistance (950-1930 ohms). Check the toothed wheel for tooth condition and axial run-out. Check the condition of the toothed wheel. |
| FMI 12 | ABS unit internal fault. Repair: Replace the ABS unit. |
| FMI 13 | Wheel size mismatch (difference above 30%). Repair: Check the tyre size. Drive a few kilometres. If the faults persist, change the tyre size. |
| FMI 1 | Wheel speed sensor (rear left (axle 2)): sensor air gap too large (signal below normal) |
| FMI 2 | Wheel speed sensor (rear left (axle 2)): unstable data / bus error (deviation >10-14%) |
| FMI 3 | Wheel speed sensor (rear left (axle 2)): sensor short circuit to battery (voltage above normal) |
| FMI 4 | Wheel speed sensor (rear left (axle 2)): sensor short circuit to ground (voltage below normal) |
| FMI 5 | Wheel speed sensor (rear left (axle 2)): sensor circuit open (current below normal) |
| FMI 6 | Wheel speed sensor (rear left (axle 2)): internal sensor short circuit (current above normal / short to ground) |
| FMI 7 | Wheel speed sensor (rear left (axle 2)): sensor/tone ring periodicity error |
| FMI 8 | Wheel speed sensor (rear left (axle 2)): abnormal signal frequency/amplitude/period |
| FMI 9 | Wheel speed sensor (rear left (axle 2)): abnormal or missing signal, harness miswired |
| FMI 10 | Wheel speed sensor (rear left (axle 2)): wheel speed signal lost |
| FMI 11 | Wheel speed sensor (rear left (axle 2)): wheel speed abnormal |
| FMI 12 | Wheel speed sensor (rear left (axle 2)): tone ring damaged / abnormal rotational frequency |
| FMI 1 | Air Gap |
| FMI 2 | Incorrect Tire |
| FMI 3 | Shorted to UBATT |
| FMI 4 | Shorted to Ground |
| FMI 5 | Open Circuit |
| FMI 6 | Short Circuit |
| FMI 7 | Incorrect Tone Ring |
| FMI 8 | Excessive Slip |
| FMI 9 | Wires Mismatched |
| FMI 10 | Speed Drop-Out |
| FMI 11 | Abnormal Speed (Chatter) |
| FMI 12 | Frequency Too High |
Do not drive. Stop as soon as it’s safe to do so — don’t keep going.
Part of the brake circuit or ABS/EBS is out of service. The pedal may still feel normal — until the first emergency stop or descent.
Next comes longer stopping distance, a skid on a slick surface, failure on a long downgrade. This is the case where "I will take it slow" does not work.
Let the air system build to working pressure and listen for leaks. Don’t drive with faulty brakes.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.