CAN network

U0115 — Lost Communication With ECM/PCM (Alternate ID)

Severity: high Drive with care, to a shop

What U0115 means

U0115 means one or more control modules stopped receiving messages from the engine or powertrain control module (ECM/PCM) over the vehicle network. Modules normally share data over a CAN bus made of two twisted wires. This code is an alternate identifier for the same fault as U0100, used on some vehicles with a gateway or dual-controller layout.

Symptoms

  • Engine won't start or stalls
  • Several warning lights on at once
  • Instrument cluster, transmission or other modules not working
  • Scan tool can't reach several modules
  • Engine or transmission in limp mode

Possible causes

  1. Open, shorted or chafed CAN bus wiring
  2. Corroded connectors or terminals
  3. Power or ground fault at the ECM/PCM
  4. Faulty module loading down the bus
  5. Gateway or message routing fault
  6. Failed ECM/PCM itself
  7. Low battery voltage or voltage drops

How to diagnose

  1. Check battery voltage and terminal condition
  2. Run a full-module scan to see which modules respond and which don't
  3. Read any other U-codes and record freeze frame data
  4. Check fuses and relays that feed the ECM/PCM
  5. Test ECM/PCM power and grounds with a multimeter
  6. Measure CAN bus resistance at the diagnostic connector (typically about 60 ohms) and check CAN-H and CAN-L voltages
  7. Inspect harnesses and connectors at the ECM/PCM and gateway for damage or corrosion
  8. Unplug suspect modules one at a time, only following a documented factory procedure

Common fixes

  • Repair or replace damaged CAN bus wiring
  • Clean or replace corroded connectors and terminals
  • Repair power and ground circuits to the ECM/PCM
  • Replace a module that is loading the bus
  • Replace or reprogram the ECM/PCM or gateway once confirmed faulty

Questions and answers

How is U0115 different from U0100?

They describe the same problem: lost communication with the engine control module. Some manufacturers simply use U0115 as an alternate ID, for example with a gateway or two controllers.

Can I drive with a U0115 code?

It's best not to. The engine may stall or not start, and modules can't share data properly. Find the cause first.

What should I check first for U0115?

Start with the battery, fuses, and ECM/PCM power and grounds. Then inspect the wiring and measure CAN bus resistance at the diagnostic connector.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.