What does SPN 1056 FMI 3 (1056/3) mean?

Electronic Pressure Control, Trailer Control: voltage above normal or shorted high.

What does SPN 1056 FMI 4 (1056/4) mean?

Electronic Pressure Control, Trailer Control: voltage below normal or shorted to ground.

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SPN 1056 — Electronic Pressure Control, Trailer Control

Q: Can I keep driving with code SPN 1056 (Electronic Pressure Control, Trailer Control)?

Safe to drive. Below — how much time you have and what happens if you keep going.

Safe to driveDrivable, but watch it yourself

Updated: 2026-11-10

J1939 code SPN 1056. Below — how the fault is worded at the factory by Bendix ABS/ESP, KAMAZ EBS3, Knorr-Bremse EBS, MAN and Renault Trucks, and what the second half of the code (FMI) means in the standard.

How to check it yourself

Trailer control in the tractor's electronic brake system (EBS): a proportional valve in the trailer control valve. The EBS unit sets the pressure in the trailer's yellow (control) line through it.

What it should read

Pressure in the red (supply) head	usually 7.0…8.1 bar
Pressure to the trailer	not more than 8.5 bar

Check order

FMI 3, 4, 5, 6: the connector on the trailer control valve — it is on the frame at the back of the cab, in dirt. Check the coil and the wires to the EBS unit for continuity.
FMI 7, 13: the pressure is not what was commanded. Connect a gauge to the yellow head, press the brake, and compare with what the diagnostics shows.
Trailer control valve: dirt and water inside — from a failed air dryer.
A leak in the yellow line up to the head, or in the head — the valve cannot hold the pressure.

Common causes — from most to least frequent

Connector on the trailer control valve.
Dirt and water in the valve.
Leak in the line to the trailer.
The valve itself.

Bendix ABS/ESP KAMAZ EBS3 Knorr-Bremse EBS MAN Renault Trucks

Bendix ABS/ESP

FMI 3	Trailer PMV REL Solenoid Shorted to Voltage; Trailer PMV HLD Solenoid Shorted to Voltage
FMI 4	Trailer PMV REL Solenoid Shorted to Ground; Trailer PMV HLD Solenoid Shorted to Ground
FMI 5	Trailer PMV REL Solenoid Open Circuit; Trailer PMV HLD Solenoid Open Circuit; Trailer PMV CMN Open Circuit
FMI 7	Trailer 3/2 valve (pressure modulator) — mechanical fault

EBS3 brakes (WABCO)

FMI 3	Electronic pressure control, trailer control: voltage above normal or short circuit
FMI 4	Electronic pressure control, trailer control: voltage below normal or short circuit
FMI 5	Electronic pressure control, trailer control: current below normal or open circuit
FMI 7	Electronic pressure control, trailer control: mechanical system not responding or out of adjustment
FMI 13	Electronic pressure control, trailer control: out of calibration

Knorr-Bremse EBS

FMI 3

Module trailer control, adjustable max pressure. Not identified

MAN

FMI 3

Module trailer control adjustable maximum pressure - Not identified

Renault Trucks

FMI 7	Trailer control module pneumatic fault or module internal fault. Repair: Check the air supply pressure, the minimum pressure switches and the pneumatic circuit of the trailer module. Check the parking brake. Clear the fault codes. If the fault persists, replace the trailer brake control module.
FMI 9	Trailer control module internal fault, or communication failure between the additional axle module, the EBS unit and the trailer control module. Repair: Check the electrical connections between the EBS unit and the trailer control module (continuity of the 4 wires X3/3, 6, 9, 12). Check the supply of the EBS unit (positive on X1/7, X1/8 and negative on X1/10, X1/12) and of the module (X3/3 and X3/12). Check the fuses that belong to the EBS. Clear the fault codes. If the fault persists, replace the trailer control module.
FMI 11	Incompatibility between the trailer control module and the EBS unit. Repair: Check the part numbers of the module and the EBS unit.
FMI 12	Trailer control module internal fault. Repair: Clear the fault codes. If the fault persists, replace the trailer control module.
FMI 13	Trailer control module internal fault. Repair: Perform the programming. Clear the fault codes. If the fault persists, replace the trailer control module.
FMI 16	Trailer control module internal fault. Repair: Clear the fault codes. If the fault persists, replace the trailer control module.

What FMI means in J1939

SPN 1056 FMI 31056/3 · 1056.3	voltage above normal or shorted high
SPN 1056 FMI 41056/4 · 1056.4	voltage below normal or shorted to ground
SPN 1056 FMI 51056/5 · 1056.5	current below normal or open circuit
SPN 1056 FMI 71056/7 · 1056.7	mechanical system not responding
SPN 1056 FMI 91056/9 · 1056.9	abnormal update rate
SPN 1056 FMI 111056/11 · 1056.11	root cause not known
SPN 1056 FMI 121056/12 · 1056.12	faulty device or component
SPN 1056 FMI 131056/13 · 1056.13	calibration out of range
SPN 1056 FMI 161056/16 · 1056.16	above normal — moderate severity

Can I keep driving

Safe to drive. Below — how much time you have and what happens if you keep going.

What happens if you keep driving

Time you have: Drivable, but watch it yourself

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.

Nearby: other

SPN 1041Start Signal Indicator
SPN 1042Tractor/Trailer Electronic Interface
SPN 1045Stop Lamp Switch #1
SPN 1048Backup Pneumatic Pressure Control, Axle 1
SPN 1054Backup Pneumatic Pressure Control, Axle 3
SPN 1057Backup Pneumatic Pressure Control, Trailer Control
SPN 1062Lining Wear Sensor, Axle 2, Left
SPN 1065Lining Wear Sensor, Axle 3, Right
SPN 1068Brake Signal Sensor #2
SPN 1081"Wait to Start" Lamp

Related codes

SPN 979Remote PTO Preset Speed Control Switch
SPN 974Remote Accelerator Pedal Position
SPN 970Engine Auxiliary Shutdown Switch
SPN 925Auxiliary Output #2
SPN 1188Turbocharger 1 Wastegate Actuator
SPN 920Audible Alarm
SPN 1194Anti-Theft System Encryption Key Present Indicator
SPN 1213Malfunction Indicator Lamp (MIL)

Makes with this code

MANRenault Trucks Bendix ABS/ESP KAMAZ EBS3Knorr-Bremse EBS

What SPN 1056 refers to

SPN 1056 is the electronic pressure control for the trailer control valve in an electronic braking system. The valve sets the brake pressure sent to the trailer line, and the electronics check its circuit and, on many systems, compare commanded and measured pressure.

FMI 2 - erratic signal or the pressure does not match the command (a frequent search).
FMI 5 - open circuit: the wire, the plug or the coil.
FMI 6 and 4 - short to ground or low voltage.
FMI 3 - voltage high or shorted to supply.
FMI 7 - the valve is mechanically stuck.

Checks

The 7-pin and 15-pin connectors between tractor and trailer, and the coiled air hoses: leakage or a loose connection.
The trailer control valve connector: corrosion and water.
Air pressure in the supply line, with the gauge, to rule out a leak that looks like a valve fault.
Brake-pressure sensor in the trailer line, where fitted.

Compare the commanded and measured pressure in the scan tool while applying the brake. A good valve follows the command within a small margin. Only if wiring and plugs are clean should the valve be replaced.

Can you keep driving?

Brake performance of the combination may be reduced, because the trailer brake pressure is not controlled correctly. Drive carefully with a lighter load and shorter speeds until you have it checked.

Questions and answers

Does SPN 1056 appear without a trailer?

It can, if the system tests the valve circuit regardless. A code with no trailer points to the tractor-side valve or harness.

Could it be only a connector problem?

Yes, quite often. Check connectors and hoses first.

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