Do not driveMinutes
J1939 code SPN 20. Below — how the fault is worded at the factory by Ford Trucks, Renault Trucks and ZF AS-Tronic, and what the second half of the code (FMI) means in the standard.
Ford TrucksRenault TrucksZF AS-Tronic
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 0 | Cruise Control Lever / Double Push. FODP code (scan tool): P0579-00. |
| FMI 1 | Predictive speed stabilizer module electrical – connection failure. FODP code (scan tool): P162D-02. |
| FMI 5 | Short to 0 V. Repair: Check the wiring between the control unit and the clutch actuator (X1B/12, X1B/17). Run the diagnostic check of the clutch actuator. 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 5 | Short circuit to ground on valve Y16 output (clutch fast release). |
| SPN 20 FMI 020/0 · 20.0 | data above normal range (most severe level) |
| SPN 20 FMI 120/1 · 20.1 | data below normal range (most severe level) |
| SPN 20 FMI 520/5 · 20.5 | current below normal or open circuit |
Do not drive. Stop as soon as it’s safe to do so — don’t keep going.
The engine is already past its temperature limit. An aluminium head goes fast: first the geometry warps, then the gasket burns through.
Next comes a blown head gasket, a damaged head and, at worst, a cracked block. Shut it down and let it cool — never open the expansion tank cap while hot.
This is an electrical fault: the sensor or its wiring is lying, not the cooling system. The temperature gauge is unreliable now and the fan may not kick in on time. Watch the coolant level and keep the engine off load on long climbs.
Let the engine cool — never open the expansion tank cap while hot. Then check the level and the hoses.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.