Safe to driveDrivable, but watch it yourself
SPN 520204 is a manufacturer number outside the standard J1939 table: different makes can put different things under it. Below — how it is worded by KAMAZ, MAZ, Volvo and YaMZ, and what the second half of the code (FMI) means.
| FMI 2 | Engine brake mode selector switches |
| FMI 2 | Engine brake button status fault - Invalid switch combination. Blink code: 3-4-2. Repair: Check the engine brake switch and its wiring. |
| FMI 5 | LCM output current to the lamps is below 0.5 A. Open wires between the LCM and the lamps, open wire between the lamp and the ground point, or lamp failure. |
| FMI 6 | LCM output current to the lamps is above 10.5 A. Wire shorted to ground between the LCM and the lamps. Possibly several additional lamps are connected, or higher-wattage lamps are installed. |
| FMI 2 | Engine brake button status fault (Invalid switch combination). Blink code: 3-4-2. Repair: Check the engine brake switch and its wiring. |
Safe to drive. Below — how much time you have and what happens if you keep going.
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.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.