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SPN 24 — Alternator Coolant Temperature

Do not driveMinutes

J1939 code SPN 24. Below — how the fault is worded at the factory by Ford Trucks, and what the second half of the code (FMI) means in the standard.

Ford Trucks

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 0Urea Return Line Error. FODP code (scan tool): P204B-00.
FMI 1Urea Dosing System Pressure – High Level 1. FODP code (scan tool): P204D-22.
FMI 2Urea Dosing System Pressure – Low. FODP code (scan tool): P204C-21.
FMI 3Urea Dosing System Pressure – High Level 2. FODP code (scan tool): P204D-85.
FMI 4Urea Dosage System Pressure – 2. FODP code (scan tool): P20E8-01.
FMI 5Urea Dosage System Pressure – 1. FODP code (scan tool): P20E8-00.
FMI 6Ure Pump Module Retract Valve Internal Fault. FODP code (scan tool): P204B-34.
FMI 7Urea Pump Module Temperature Value – Out of Range. FODP code (scan tool): P20AD-02.
FMI 9Urea Pump Module Communication Failure. FODP code (scan tool): P20B6-00.

What FMI means in J1939

SPN 24 FMI 024/0 · 24.0data above normal range (most severe level)
SPN 24 FMI 124/1 · 24.1data below normal range (most severe level)
SPN 24 FMI 224/2 · 24.2data erratic or intermittent
SPN 24 FMI 324/3 · 24.3voltage above normal or shorted high
SPN 24 FMI 424/4 · 24.4voltage below normal or shorted to ground
SPN 24 FMI 524/5 · 24.5current below normal or open circuit
SPN 24 FMI 624/6 · 24.6current above normal or grounded circuit
SPN 24 FMI 724/7 · 24.7mechanical system not responding
SPN 24 FMI 924/9 · 24.9abnormal update rate

Can I keep driving

Do not drive. Stop as soon as it’s safe to do so — don’t keep going.

What happens if you keep driving

Time you have: Minutes

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.

What to check on the spot

Let the engine cool — never open the expansion tank cap while hot. Then check the level and the hoses.

Nearby: cooling

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