U0138

Universal

Lost Communication With All Terrain Control Module

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The vehicle has detected that it cannot communicate with the all-terrain control module over its communication network. That module may coordinate terrain-related functions, so those functions or related displays may be unavailable. The code identifies a communication problem, not proof that the module itself has failed.

Report an error with this code

⚠️ Before You Begin (Safety First)

If terrain-related controls or vehicle behavior seem abnormal, avoid relying on those functions and stop somewhere safe if the vehicle feels difficult to control. Seek prompt diagnosis if warning messages appear or traction, braking, or handling is affected.

Common Symptoms

  • A terrain-control warning message or indicator may appear if the vehicle reports that the module is unavailable.
  • Terrain-related modes or functions may not respond or may be unavailable, depending on the vehicle's equipment.
  • Other modules may record communication faults if they cannot exchange information with this module.
  • There may be no noticeable symptoms if the affected function is not being used or the communication interruption is intermittent.

Common Causes

  • A loose, damaged, corroded, or poorly connected module connector can interrupt communication.
  • Damaged wiring or a fault elsewhere in the vehicle communication network can prevent messages from reaching the module.
  • A problem with the module's power supply or ground can make it stop communicating.
  • Low or unstable vehicle battery voltage may interrupt module operation or communication.
  • The all-terrain control module may have an internal fault, but the code alone does not establish that.

Diagnostic Steps

  1. Note any warning messages and whether terrain-related functions changed; this helps a technician connect the code to the symptoms.
  2. Check the vehicle's battery condition and look for obvious loose or damaged battery connections, since unstable power can affect module communication.
  3. With the vehicle safely parked and switched off, visually inspect accessible related wiring and connectors for obvious damage, looseness, or corrosion. Do not disconnect components unless the vehicle-specific service information says it is safe.
  4. Record the code and any other stored codes before clearing anything. Related codes can help distinguish a single-module issue from a broader network or power problem.
  5. If the code returns, or a connector or wiring fault is suspected, arrange vehicle-specific electrical diagnosis rather than replacing the module based on this code alone.

When to Call a Professional

Use vehicle-specific service information to identify the relevant module and network. A technician can scan all modules for related communication codes, check module power and grounds, inspect connectors and network wiring, and determine whether another network fault or the module itself is responsible before replacing parts.

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Commonly Asked Questions

Does U0138 prove that the all-terrain control module has failed?

No. It indicates lost communication with the module. Power, ground, connector, wiring, network, or voltage problems can produce the same detected condition.

Can I keep driving with U0138?

It depends on whether vehicle behavior or terrain-related functions are affected. If handling, traction, braking, or another important function seems abnormal, stop safely and have the vehicle checked.

Why are there other communication codes as well?

Several modules may report communication problems when a shared network, power supply, or ground is disrupted. A full-module scan helps identify whether the issue is isolated or broader.

Will clearing the code fix the problem?

Clearing it may remove the stored warning temporarily, but it does not repair the cause. If communication is still interrupted, the code may return.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.