U0115: Lost Communication With ECM/PCM "B"
Other control units no longer receive messages from the Second Engine Control Module.
High risk
Have it checked soon. The engine may run poorly, limit power or fail to start.
Short answer · Can I keep driving with U0115?
Usually yes, with care. The engine may run poorly, limit power or fail to start. Have the network and the module checked soon.
What does U0115 mean?
Code U0115 means a control unit expected regular messages from the ECM/PCM "B" on the vehicle network and they stopped arriving. A power or ground fault at that module, a damaged network wire or corroded connector, low battery voltage or a failed module are typical causes.
What the car does when the code is set
Other modules cannot receive data from the engine or transmission module. The engine may not start, the gearbox may go into limp mode and several warning lights can come on at once.
How the system works
The engine and transmission control modules share data with other modules over the network, such as engine speed, torque and gear. Each module expects regular messages; when they stop arriving for a set time, a lost communication code is stored.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Power or ground fault at the moduleA blown fuse, failed relay or poor ground switches the module off the network.
- Wiring fault in the network linesDamaged or corroded CAN wires between modules.
- Low battery voltageVoltage drops during cranking can cause temporary lost communication.
- Failed control moduleLess common than wiring and power faults, but possible.
- Water damageModules and connectors exposed to water corrode.
How it is diagnosed
- Note how the car behavesIf the engine does not start or the gearbox is in limp mode, the module may really be offline. If everything works, the code may be an old, intermittent event.
- Check fuses, relays and groundsUse the fuse diagram for the engine or transmission control module.
- Check battery voltageCharge or test the battery before deeper diagnosis.
- Scan all modules and test the networkA workshop checks whether the module answers the scan tool and measures the CAN lines.
Questions about U0115
Can a weak battery cause U0115?
Yes. Low voltage during starting can make modules drop off the network for a moment and store this code. Check the battery before replacing any module.
Does lost communication always mean a bad module?
No. Power, ground and wiring faults are more common causes than a failed module.