Safe to driveUntil the next service
SPN 388 is a manufacturer number outside the standard J1939 table: different makes can put different things under it. Below — how it is worded by Ford Trucks, and what the second half of the code (FMI) means.
Ford Trucks/Ecotorq writes fault numbers in its own format: the code in the table below is a Ford code (hexadecimal, zero-padded), not a J1939 SPN. It matches the standard only where the signal itself is standard, and usually matches the title of this page by digit alone.
| FMI 21 | J1939 Signal Error: Missing EBC2 message |
| FMI 70 | J1939 Signal Error: Error in EBC2 Front Axle |
| FMI 71 | J1939 Signal Error: Not Available EBC2 Front Axle |
| SPN 388 FMI 21388/21 · 388.21 | data drifted low |
Safe to drive. Below — how much time you have and what happens if you keep going.
A standalone fault with no immediate consequences for driving.
Show the codes at the next service. If a second code from the same system appears, stop putting it off.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.