U0115
Lost Communication with ECM/PCM "B"
The ECM/PCM "B" has stopped transmitting on the vehicle data bus, so other control units no longer receive its messages. A second engine/powertrain controller is unreachable, which can prevent the engine from running. Typical causes are loss of power or ground at the module, an open or shorted CAN/LIN bus wire, a connector fault, or an internal module failure.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
Ordered by how often each turns out to be the cause.
- Secondary ECM unpoweredCommon
- CAN wiring to secondary ECM brokenPossible
- Gateway module routing CAN messages incorrectlyLess likely
Parts involved
- ECM
- CAN Bus Wiring
U0115 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.