Safe to driveEnough to reach the yard
J1939 code SPN 51. Below — how the fault is worded at the factory by MAZ, Meritor (ex-WABCO), SITRAK, YaMZ and ZF AS-Tronic, and what the second half of the code (FMI) means in the standard.
MAZMeritor (ex-WABCO)SITRAKYaMZZF AS-Tronic
| FMI 2 | Intake throttle valve stuck - Valve/damper stuck. Blink code: 6-7-4. Repair: Check the intake throttle actuator. |
| FMI 3 | Intake throttle control valve fault - Control signal above allowed. Blink code: 6-7-3. Repair: Check the intake throttle control valve and its wiring. |
| FMI 4 | Intake throttle control valve fault - Control signal below allowed. Blink code: 6-7-3. Repair: Check the intake throttle control valve and its wiring. |
| FMI 12 | Intake throttle actuator error - General error. Blink code: 6-7-8. Repair: Check the intake throttle actuator and its wiring. |
| FMI 20 | Intake throttle position control error, sustained deviation - Trim coefficient drifted far from its initial value. Blink code: 6-7-5. Repair: Check the intake throttle actuator. |
| FMI 21 | Intake throttle position control error, deviation from target - Trim coefficient changed sharply within a drive cycle. Blink code: 6-7-9. Repair: Check the intake throttle actuator. |
| FMI 3 | Power Amp. Out Valve Right Rear — Shorted to Battery |
| FMI 5 | Power Amp. Out Valve Right Rear — Open Circuit |
| FMI 6 | Power Amp. Out Valve Right Rear — Short to Ground |
| FMI 0 | TPS1 opening angle greater than TPS2 |
| FMI 1 | TPS1 opening angle less than TPS2 |
| FMI 2 | Throttle valve mechanical stop learning value drifted out of range. Scan tool code: P2108. Effect: Fan and warm-up control may misbehave. |
| FMI 3 | High voltage on TPS1 |
| FMI 4 | Low voltage on TPS1 |
| FMI 5 | Throttle valve actuator circuit open load. Scan tool code: P2100. Effect: Torque may be limited. |
| FMI 7 | Unable to reach higher TPS opening angle |
| FMI 8 | Long-term drift of the throttle valve closed-position learning value. Scan tool code: P2108. Effect: Fan and warm-up control may misbehave. |
| FMI 9 | Long-term drift of the throttle valve open-position learning value. Scan tool code: P2108. Effect: Fan and warm-up control may misbehave. |
| FMI 11 | Intermittent throttle valve fault. Scan tool code: P2620. Effect: Torque may be limited. |
| FMI 12 | Throttle valve governor deviation at cold start. Scan tool code: P2112. Effect: Fan and warm-up control may misbehave. |
| FMI 13 | Throttle valve feedback sensor voltage above the upper limit. Scan tool code: P2622. Effect: Torque may be limited. |
| FMI 14 | Throttle valve feedback sensor voltage below the lower limit. Scan tool code: P2621. Effect: Torque may be limited. |
| FMI 15 | Throttle valve fully-open learning value beyond the limit. Scan tool code: P2108. Effect: Fan and warm-up control may misbehave. |
| FMI 16 | Persistent negative throttle valve governor deviation. Scan tool code: P2111. Effect: Fan and warm-up control may misbehave. |
| FMI 17 | Throttle valve closed-position learning value beyond the limit. Scan tool code: P2108. Effect: Fan and warm-up control may misbehave. |
| FMI 18 | Persistent positive throttle valve governor deviation. Scan tool code: P2112. Effect: Fan and warm-up control may misbehave. |
| FMI 20 | Throttle valve position signal above the mechanical maximum. Scan tool code: P2101. Effect: Fan and warm-up control may misbehave. |
| FMI 21 | Throttle valve position signal below the mechanical minimum. Scan tool code: P2101. Effect: Fan and warm-up control may misbehave. |
| FMI 22 | Short-term drift of the throttle valve closed-position learning value. Scan tool code: P2108. Effect: Fan and warm-up control may misbehave. |
| FMI 23 | Short-term drift of the throttle valve open-position learning value. Scan tool code: P2108. Effect: Fan and warm-up control may misbehave. |
| FMI 24 | Over-temperature of the throttle valve powerstage. Scan tool code: P2101. |
| FMI 31 | TPS1/2 tracking voltage out of range |
| FMI 2 | Intake air throttle valve seized (Valve seized). Blink code: 6-7-4. Repair: Check the intake throttle actuator. |
| FMI 3 | Intake air throttle valve control valve fault (Control signal above allowable limit). Blink code: 6-7-3. Repair: Check the intake throttle control valve and its wiring. |
| FMI 4 | Intake air throttle valve control valve fault (Control signal below allowable limit). Blink code: 6-7-3. Repair: Check the intake throttle control valve and its wiring. |
| FMI 12 | Intake air throttle valve actuator fault (General fault). Blink code: 6-7-8. Repair: Check the intake throttle actuator and its wiring. |
| FMI 20 | Intake air throttle valve position control fault, sustained deviation (Adaptation coefficient deviated significantly from initial value). Blink code: 6-7-5. Repair: Check the intake throttle actuator. |
| FMI 21 | Intake air throttle valve position control fault, deviation from target (Adaptation coefficient deviated significantly over the drive cycle). Blink code: 6-7-9. Repair: Check the intake throttle actuator. |
ZF AS-Tronic uses its own fault numbering: the number in the table below is an internal ZF code, not a J1939 SPN. It matches the title of this page by digit only and means something different.
| FMI 10 | Fault on valve Y15 output circuit (clutch slow engagement). |
Safe to drive. Below — how much time you have and what happens if you keep going.
Boost is not reaching its target: turbo, intercooler or intake. The engine compensates with mixture and runs hotter than usual.
You will lose pull, burn more fuel and add overheating on long climbs. If you hear a whine or a whistle from the turbo, stop — the wheel is breaking up.
This is an electrical fault: an open, a short or a bad contact in the sensor circuit. The value it measures is most likely fine. You can drive. But until the circuit is repaired this system runs blind and cannot warn you about a real failure.
That said, the manufacturer flags this code as critical — if in doubt, it is safer to stop and check on the spot.
Inspect the air filter and charge-air hoses: leaks and cracks produce exactly these codes.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.