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SPN 46 — Pneumatic system pressure (primary reservoir)

Do not driveMinutes

J1939 code SPN 46. Below — how the fault is worded at the factory by Ford Trucks and ZF AS-Tronic, 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 0APU-Air Dryer Pressure Sensor Communication Error. FODP code (scan tool): U0129-00.
FMI 1Intarder Module CAN Communication Error. FODP code (scan tool): U0400-01.
FMI 2Cruise Control System CAN Communication Error. FODP code (scan tool): U0405-00.
FMI 3ABS / EBS Module CAN Communication Error. FODP code (scan tool): U0418-00.
FMI 8BCU Module CAN Communication Error. FODP code (scan tool): U019B-00.
FMI 9BCU Module CAN Communication Error. FODP code (scan tool): U019B-01.
FMI 9PDS_CCVS timeout

ZF AS-Tronic

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 0Fault on the ZF E-module output to the power take-off 2 (PTO2) valve.

What FMI means in J1939

SPN 46 FMI 046/0 · 46.0data above normal range (most severe level)
SPN 46 FMI 146/1 · 46.1data below normal range (most severe level)
SPN 46 FMI 246/2 · 46.2data erratic or intermittent
SPN 46 FMI 346/3 · 46.3voltage above normal or shorted high
SPN 46 FMI 846/8 · 46.8abnormal frequency or pulse width
SPN 46 FMI 946/9 · 46.9abnormal 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

Part of the brake circuit or ABS/EBS is out of service. The pedal may still feel normal — until the first emergency stop or descent.

Next comes longer stopping distance, a skid on a slick surface, failure on a long downgrade. This is the case where "I will take it slow" does not work.

What to check on the spot

Let the air system build to working pressure and listen for leaks. Don’t drive with faulty brakes.

Which codes follow

If the value really did go out of range, rather than a sensor circuit being broken, these normally light up after it:

They are not fixed separately — they go out together with this one. The list is deliberately short: only the links the reference is sure about.

Nearby: brakes

Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.