U0259

Lost Communication With Passenger Seat Control Module A

U0259 is a generic OBD-II network diagnostic trouble code: Lost Communication With Passenger Seat Control Module A. 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
U0259
Group
Network
System
Network
Severity
Information only
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What U0259 means

U0259 indicates that the BCM or comfort gateway has lost serial data communication with the Passenger Seat Control Module A. This module governs primary power-seat adjustment functions on the front passenger side, including fore-aft travel, seat back recline, and height adjustment. On vehicles with passenger-side memory seat or advanced seating options, Module A also handles the primary position storage and recall logic for the passenger seat.

As with driver-side seat codes, U0259 is a low-severity code because seat positioning is a comfort feature and not related to safety-critical or emissions systems. The MIL may or may not illuminate depending on the calibration strategy. Affected functions are limited to the passenger seat adjustments; no powertrain or braking effects are expected.

The most productive starting point is a physical inspection of the under-seat wiring on the passenger side. Unlike the driver seat, passenger seat wiring is less likely to be damaged by frequent movement but can be damaged by cargo placement, items wedged under the seat, or an infrequent but sudden overload when heavy cargo is placed on the seat. Inspect the harness routing from the floor connector to the module, and verify the connector is fully seated.

Common causes

Most-frequently reported root causes when U0259 is logged.

  • 1
    Harness damage under the passenger seat from cargo or objects placed against the wiring.
  • 2
    Corroded or unseated connector at the Passenger Seat Control Module A.
  • 3
    Liquid spill that reached the under-seat module or its wiring.
  • 4
    Blown fuse for the passenger seat module.
  • 5
    Failed seat module A hardware.
  • 6
    Open or short on the data bus segment serving the passenger seat module.

Symptoms drivers notice

MIL or comfort/convenience warning lamp illuminated.
Passenger-side power seat adjustments inoperative.
Passenger seat memory position recall non-functional.
No powertrain, braking, or emissions system effects.

How to diagnose U0259

A typical diagnostic flow when this code is present.

  1. 1
    Record all DTCs; confirm no related passenger-restraint codes are stored alongside U0259.
  2. 2
    Inspect under the passenger seat for harness damage, pinching, or connector displacement.
  3. 3
    Verify supply voltage and ground at the passenger seat module A connector.
  4. 4
    Check the seat-module fuse and any in-line fusible links.
  5. 5
    Use a scan tool to attempt communication with the passenger seat module A.
  6. 6
    Repair any identified wiring fault, clear codes, and verify seat movement.
  7. 7
    Replace the module if wiring and power circuits are confirmed good and the module is unreachable.

Related network codes

Frequently asked questions

Why would U0259 appear after a car wash or flood event?

Water can enter the vehicle cabin and pool under the seat, shorting the bus wiring or corroding the module connector. After a flooding event, all under-seat modules and wiring should be inspected for moisture damage before attempting to clear codes.

Does U0259 affect the passenger airbag?

The passenger seat comfort module and the occupant classification or airbag system are separate modules on separate bus segments in most architectures. Verify airbag system operation with dedicated airbag-module diagnostics rather than assuming U0259 impacts it.

Can I use the passenger seat manually if Module A has failed?

If the seat has a manual adjustment option, yes. If it is fully electric with no manual override, the seat will be locked in its current position until the module is repaired.

Is U0259 the same as U0260?

No. U0259 refers to the Passenger Seat Control Module A (primary functions), while U0260 refers to Passenger Seat Control Module B (secondary functions such as lumbar and bolster). They identify different nodes on the same seat.

Disabling U0259 in software

RaceTune can permanently disable U0259 — 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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