U0115

Universal

Lost Communication With ECM/PCM B

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 detected that it could not communicate with the controller identified as ECM/PCM B. This controller is involved in engine or powertrain management, so loss of communication may affect drivability or prevent the vehicle from starting. The code identifies a communication problem, not proof that the controller itself has failed.

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⚠️ Before You Begin (Safety First)

If the vehicle stalls, loses power, will not respond normally, or shows other serious warnings, pull over safely and arrange assistance rather than continuing to drive. If it runs normally, have the communication fault diagnosed promptly; symptoms can change if the problem becomes persistent.

Common Symptoms

  • The check-engine or another warning light may be on if the communication loss affects the vehicle or is reported by another module.
  • The engine may run poorly, enter a reduced-power mode, or have missing powertrain functions if the controller cannot provide or receive needed information.
  • The vehicle may crank without starting or may not start if the affected controller's communication loss prevents normal powertrain operation.
  • Other modules may show warnings or missing data because they cannot communicate with ECM/PCM B.
  • There may be no noticeable symptoms if the fault was intermittent or is stored from an earlier event.

Common Causes

  • A loose, damaged, corroded, or poorly connected network wire or connector may interrupt communication.
  • A power supply or ground problem at ECM/PCM B may prevent it from operating or communicating.
  • Low or unstable vehicle battery voltage may disrupt module operation or network communication.
  • A fault elsewhere on the vehicle communication network may interfere with messages to or from ECM/PCM B.
  • ECM/PCM B may have an internal fault, but this should be considered only after its power, ground, connections, and network circuits are checked.

Diagnostic Steps

  1. Note any warning lights, starting problems, or drivability changes, and avoid driving if the vehicle is unsafe or behaving unpredictably.
  2. Check whether the battery appears discharged or the terminals are visibly loose or corroded; poor electrical supply can affect module communication.
  3. With the vehicle off, visually inspect accessible wiring and connectors related to the engine-control system for looseness, damage, or corrosion. Do not disconnect components unless the vehicle's service information says it is safe.
  4. If you have a scan tool, record the codes from all modules and whether U0115 is current or stored. Other communication codes can help identify a broader network or power-supply issue.
  5. Use model-, year-, and engine-specific service information for further checks. Leave network circuit testing or module replacement to a qualified technician if you lack suitable equipment or procedures.

When to Call a Professional

A technician can scan all available modules to see whether other communication codes are present and whether this code is current or stored. Diagnosis may include checking the relevant controller’s power and ground, inspecting network wiring and connectors, and testing communication circuits using vehicle-specific service information. The code alone does not justify replacing the ECM/PCM.

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Commonly Asked Questions

Does U0115 prove that ECM/PCM B needs replacement?

No. It reports lost communication with the controller identified as ECM/PCM B. Wiring, connectors, power, ground, battery voltage, or another network fault can cause the same condition.

Can I drive with U0115?

It depends on how the vehicle behaves. If it stalls, loses power, will not start reliably, or has serious warnings, stop driving when safe and arrange assistance. If it seems normal, arrange diagnosis promptly because an intermittent fault can worsen.

Why might there be no symptoms?

The communication loss may have been brief or may be stored from an earlier event. A scan of all modules and a check of whether the code is current can help distinguish an active fault from an intermittent one.

What should be checked before replacing a module?

Check the relevant power and ground supplies, connectors, network wiring, battery condition, and other module codes using vehicle-specific service information. Module replacement should follow evidence that these other causes have been ruled out.

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