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SPN 627 — Power Source

Safe to driveTo the nearest safe stop

Updated: 2026-11-14

J1939 code SPN 627. Below — how the fault is worded at the factory by Bendix ABS/ESP, DAF, Dongfeng, KAMAZ EBS3, Knorr-Bremse EBS, MAN, Meritor (ex-WABCO), Renault Trucks and WABCO ABS/ESC, and what the second half of the code (FMI) means in the standard.

How to check it yourself

The unit's power supply — a general term for "something is wrong with the power": voltage out of range, dropping out, or the unit restarting. Check it the same way as the battery voltage (SPN 168), but on this unit.

What it should read

Engine off25.2…25.6 V on the charged batteries
Engine running27.5…28.8 V
Sag at the unit connector under loadnot more than 0.5 V

Check order

  1. Which unit gave the code — each has its own supply and its own fuse.
  2. Measure the supply and the ground right at the unit's connector, with a load switched on.
  3. Oxidised contacts of the fuse, and of the unit's power relay.
  4. A code on many units at once — battery, alternator, main ground.
  5. FMI 2 (jumps): a contact that is there sometimes and not at others — wiggle the harness and watch the voltage.

Common causes — from most to least frequent

  1. Unit ground.
  2. Fuse or power relay.
  3. Battery and alternator — if codes are on many units.
  4. Unit connector.

Bendix ABS/ESPDAFDongfengKAMAZ EBS3Knorr-Bremse EBSMANMeritor (ex-WABCO)Renault TrucksWABCO ABS/ESC

Bendix ABS/ESP

FMI 2Input Voltage Excessive Noise (Temp.)
FMI 3Battery Voltage Too High; Ignition Voltage Too High
FMI 4Battery Voltage Too Low; Battery Voltage Too Low During ABS; Ignition Voltage Too Low; Ignition Voltage Too Low During ABS
FMI 5Battery Voltage Input Open Circuit
FMI 14Input Voltage Excessive Noise (Latched)

DAF

FMI 2ECU power supply, pin C4 incorrect shutdown (extended period)
FMI 12Power supply internal fault 1 (injectors, altered voltage)

Dongfeng

FMI 2Failed to save ECM data from the previous operating cycle
FMI 12Injector voltage too low

EBS3 brakes (WABCO)

FMI 0Power supply: data valid but above normal range (most severe level)
FMI 1Power supply: data valid but below normal range (most severe level)

Knorr-Bremse EBS

FMI 3Power Supply. Not identified

MAN

FMI 3Power Supply - Not identified

Meritor (ex-WABCO)

FMI 0System Overvoltage (30A) (30B)
FMI 1System Undervoltage (30A) (30B)
FMI 14Interruption of Ground (31B)
FMI 17Interruption of Terminal (30A)
FMI 18Interruption of Terminal (30B)

Renault Trucks

FMI 2Mismatch between the charge levels of the diagonal supply circuits. Repair: Check the battery charge of all the speed sensors.
FMI 3Battery charge level too high. Repair: Check the vehicle voltage.
FMI 4Battery charge level too low. Repair: Check the vehicle voltage.
FMI 5ABS unit: open circuit. Repair: Check the continuity of the ABS unit supply wiring (X1/7, X1/8, X1/9, X1/17) (fuses F49 3 A, F28 20 A)
FMI 7Current to the EBS unit too high or too low, fault not stored. Repair: Check the EBS unit supply (positive on X1/7, X1/8 and negative on X1/10, X1/12). Check the fuses that belong to the EBS.
FMI 13VECU control unit relay: control fault. Repair: Check the VECU. The relay (R 43) is faulty.

WABCO ABS/ESC

FMI 3Overvoltage

What FMI means in J1939

SPN 627 FMI 0627/0 · 627.0data above normal range (most severe level)
SPN 627 FMI 1627/1 · 627.1data below normal range (most severe level)
SPN 627 FMI 2627/2 · 627.2data erratic or intermittent
SPN 627 FMI 3627/3 · 627.3voltage above normal or shorted high
SPN 627 FMI 4627/4 · 627.4voltage below normal or shorted to ground
SPN 627 FMI 5627/5 · 627.5current below normal or open circuit
SPN 627 FMI 7627/7 · 627.7mechanical system not responding
SPN 627 FMI 12627/12 · 627.12faulty device or component
SPN 627 FMI 13627/13 · 627.13calibration out of range
SPN 627 FMI 14627/14 · 627.14manufacturer-specific instructions
SPN 627 FMI 17627/17 · 627.17below normal — low severity
SPN 627 FMI 18627/18 · 627.18below 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: To the nearest safe stop

The electrical system is not holding voltage. While the engine runs the alternator carries it; shut it off and you may not restart.

Next the lights go, then modules start dropping out and false codes appear all over the truck. Get to somewhere with help without shutting the engine down.

What to check on the spot

Check the battery terminals and earth strap — corrosion and loose clamps throw false codes all over the truck. Running voltage should be 27–29 V.

Nearby: power supply

Related codes

Makes with this code

DongfengDAFMANRenault TrucksBendix ABS/ESPKAMAZ EBS3Knorr-Bremse EBSMeritor (ex-WABCO)WABCO ABS/ESC

Related problems

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