Safe to driveDrivable, but watch it yourself
J1939 code SPN 30. Below — how the fault is worded at the factory by Meritor (ex-WABCO), Renault Trucks and ZF AS-Tronic, and what the second half of the code (FMI) means in the standard.
Meritor (ex-WABCO)Renault TrucksZF AS-Tronic
| FMI 3 | Internal Valve Relay — Cannot switch off |
| FMI 4 | Internal Valve Relay — Valve supply voltage missing or cannot switch on |
| FMI 8 | Transmission retarder CAN bus fault. Repair: Run the diagnostic check of the intarder electronic unit. Check the Astronic unit parameters. Switch the ignition off, switch it on again and repeat the test. If the fault persists, replace the control unit. |
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 8 | No CAN bus signal: "secondary retarder configuration". |
| SPN 30 FMI 330/3 · 30.3 | voltage above normal or shorted high |
| SPN 30 FMI 430/4 · 30.4 | voltage below normal or shorted to ground |
| SPN 30 FMI 830/8 · 30.8 | abnormal frequency or pulse width |
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.