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DTC codes / U01xx · Lost communication with a control module / U0115

U0115Lost Communication With ECM/PCM B

U0115 is a generic network communication code indicating that a control module on the vehicle's controller area network (CAN) bus has lost contact with the engine control module (ECM) or powertrain control module (PCM), designated as 'B'. The computer detected that expected periodic messages from the ECM/PCM stopped arriving within the required time window, which can disable communication-dependent functions and trigger the warning light.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaLost communication with a control module

Symptoms you may notice

  • Illumination of the check engine light or a dedicated communication fault warning
  • The engine may crank but fail to start because the ECM/PCM is not responding to the start request
  • Multiple unrelated warning lights on the dashboard, such as ABS, traction control, or transmission indicators
  • Erratic engine behavior, stalling, or reduced power if the ECM/PCM intermittently drops off the network
  • Often no symptoms besides the warning light when the fault is stored but communication is currently restored
  • Inoperative scan tool communication with the ECM/PCM or other modules on the same network

Common causes, most likely first

  1. Damaged, corroded, or loose wiring or connector terminals on the CAN bus circuit between the ECM/PCM and other modules
  2. Failed ECM/PCM power or ground connection, including a blown fuse or poor chassis ground
  3. Internal failure of the ECM/PCM causing it to stop transmitting or receiving network messages
  4. A shorted or open CAN bus data line, often caused by chafed wiring or water intrusion in a connector
  5. Another module on the network holding the bus down and preventing normal communication
  6. Low battery voltage or a failing charging system that causes modules to drop offline intermittently
  7. Aftermarket electronic devices improperly wired into the network or power circuits

How to diagnose and fix it

  1. Perform a complete battery and charging system test to rule out low voltage as the root cause
  2. Use a scan tool to check for communication with all modules and record which modules are online or offline
  3. Inspect the ECM/PCM connectors and the CAN bus wiring for corrosion, loose pins, chafing, or water intrusion
  4. Measure resistance and voltage on the CAN bus data lines to check for opens, shorts, or improper termination
  5. Verify power and ground at the ECM/PCM with a multimeter or test light under load
  6. If wiring and power are good, substitute a known-good ECM/PCM or perform a module communication test to confirm internal failure
  7. Repair or replace the faulty wiring, connector, or module and clear the code, then verify communication is restored

Why U0115 is often a wiring fault

  • A loose or corroded ground connection at the ECM/PCM can cause intermittent U0115 without any visible damage to the data wires, so always load-test grounds before condemning the module.
  • The code can be set by a completely different module on the same CAN bus that is shorting the data line, making the ECM/PCM appear faulty when it is actually a victim of another module's failure.
  • Low battery voltage during cranking or a failing alternator can cause modules to drop offline momentarily and store U0115, so check the charging system before replacing expensive parts.
  • Aftermarket alarms, remote starters, or poorly installed accessories tapped into the CAN bus are a common hidden cause of communication codes on otherwise healthy vehicles.
  • U0115 does not always mean the ECM/PCM is dead; it can be stored historically after a one-time glitch, so clear the code and verify whether it returns before starting repairs.

Can I keep driving with U0115?

If the engine starts and runs normally, you can drive the vehicle to a repair shop, but avoid long trips and be prepared for a possible stall or no-start condition. If the engine will not start or multiple warning lights are on, do not drive and have the vehicle towed for diagnosis.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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