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U0259 — Lost Communication Special Purpose Vehicle Control Module

Generic OBD-II · all makesNetwork / communication

U0259 indicates that the Powertrain Control Module (PCM) has lost communication with a special‑purpose vehicle control module, such as a transmission, ABS, or body control unit. This loss of communication prevents coordinated operation of the affected system.

Symptoms

What causes it — most likely first

1. Faulty special‑purpose control module

The module that the PCM is trying to communicate with (e.g., transmission control module, ABS module) has failed or is not responding.

2. Corroded or broken wiring harness

Damage, corrosion, or broken pins in the harness that carries the communication signals can interrupt data flow.

3. Poor connector contact

Loose, dirty, or oxidized connector pins at either the PCM or the secondary module can cause intermittent loss of communication.

4. Voltage drop or grounding issue

Insufficient power or a bad ground on the communication circuit can prevent the modules from staying linked.

5. PCM communication failure (rare)

A malfunction inside the PCM’s communication hardware or software may be the source, but this is far less common than external issues.

How it's diagnosed

  1. Scan for additional codes and note any related communication or system‑specific codes.
  2. Inspect the wiring harnesses and connectors between the PCM and the affected control module for damage, corrosion, or looseness.
  3. Perform a continuity and resistance test on the communication circuit to verify proper voltage and grounding.
  4. Use a scan tool to monitor live data and communication status while cycling the affected system (e.g., shift transmission, activate ABS).
  5. If all wiring and connectors are sound, test or replace the secondary control module with a known good unit before considering PCM replacement.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0250 — Lost Communication Impact ClassificatiU0251 — Lost Communication Running Board ContrU0252 — Lost Communication Lighting Control MoU0253 — Lost Communication Accessory Protocol U0254 — Lost Communication Remote Start ModuleU0255 — Lost Communication Front Display Inter

Frequently asked

Can I simply replace the PCM to fix a U0259 code?

In most cases no. The PCM is rarely the culprit; the problem is usually a faulty module, wiring, or connector. Replacing the PCM without confirming the true cause can be wasteful.

Will a blown fuse cause a U0259 code?

Yes, if the fuse protects the communication circuit. A blown fuse will cut power to the secondary module, resulting in loss of communication.

Is the U0259 code specific to a particular vehicle system?

The code is generic and can refer to any special‑purpose control module that communicates with the PCM, such as transmission, ABS, steering, or body control modules.

After fixing the wiring, does the code clear automatically?

Once the underlying issue is resolved, clear the code with a scan tool and drive the vehicle through a complete drive cycle. If the repair was successful, the code should not return.