U0256

Lost Communication With Driver Seat Control Module B

U0256 is a generic OBD-II network diagnostic trouble code: Lost Communication With Driver Seat Control Module B. It is logged by the engine control unit when the network monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
U0256
Group
Network
System
Network
Severity
Information only
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What U0256 means

U0256 is recorded when the BCM or a comfort/convenience gateway cannot receive messages from the Driver Seat Control Module B. Vehicles with advanced power seat systems often distribute seat control across two modules: module A handles fore-aft and recline, while module B controls lumbar, bolster, massage, memory positioning, or heating functions. The exact function split varies by manufacturer and vehicle line.

Because seat modules are non-safety-critical comfort devices, U0256 carries a low severity rating. The MIL may illuminate if the BCM reports the fault to the ECM via the gateway, or only an infotainment or seat-function warning may appear. Affected features will be those controlled exclusively by Module B; Module A functions typically remain unaffected.

Seat module wiring is routed under the seat cushion and through the floor harness, areas that are subject to damage from seat sliding, items dropped under the seat, and liquids. Connector inspection under the driver seat should be the first physical step. If a seat-heating or memory-seat function failed at the same time as the code appeared, that is a useful indicator that the fault is real and not a transient voltage dropout.

Common causes

Most-frequently reported root causes when U0256 is logged.

  • 1
    Harness damage under the driver seat from seat sliding on the connector or wiring.
  • 2
    Liquid spill into the seat module or under-seat wiring area.
  • 3
    Corroded or loosened connector at the Driver Seat Control Module B.
  • 4
    Blown fuse supplying the seat module B.
  • 5
    Failed seat module B hardware.
  • 6
    Open or short in the CAN or LIN data wire between the gateway and seat module B.
  • 7
    Module B not programmed after replacement.

Symptoms drivers notice

MIL or comfort-system warning illuminated.
Seat adjustment functions managed by Module B inoperative (e.g., lumbar, bolster, or memory recall).
Memory seat position recall may fail partially.
No powertrain, safety, or emissions system effects.

How to diagnose U0256

A typical diagnostic flow when this code is present.

  1. 1
    Record all DTCs and note which seat functions are inoperative.
  2. 2
    Physically inspect under the driver seat for harness pinching, cuts, and connector condition.
  3. 3
    Verify supply voltage and ground at the seat module B connector.
  4. 4
    Check the relevant seat-module fuse.
  5. 5
    Attempt scan tool communication with seat module B to see if it is present on the bus.
  6. 6
    Repair any wiring fault found; clear codes and test seat functions.
  7. 7
    If wiring is good and the module is absent from the bus, replace seat module B.

Related network codes

Frequently asked questions

Which seat functions does Module B typically control?

This is manufacturer-specific, but Module B commonly handles the secondary axes: lumbar support, side bolsters, seat heating/ventilation, or the memory-position storage function. Module A typically handles the primary fore-aft, recline, and height adjustments.

Can a spilled drink cause U0256?

Yes. Liquid spills under the seat can short the bus wiring or corrode the module connector, causing an immediate loss of communication. Thoroughly dry the area and inspect for corrosion before replacing the module.

Will U0256 affect safety systems such as airbags?

Generally no. Seat comfort modules are on a separate bus from restraint control modules. However, if the seat-position sensor used by the airbag system is routed through Module B on the specific vehicle, verify airbag operation separately.

Is this code specific to the driver seat or can it appear for the passenger seat too?

U0256 is specifically assigned to the driver seat. Separate codes exist for passenger-side seat modules. If both driver and passenger seat modules are faulted simultaneously, a shared bus or power fault is the likely cause.

Disabling U0256 in software

RaceTune can permanently disable U0256 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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