What U0115 means
The ECM/PCM "B" has stopped transmitting on the vehicle data bus, so other control units no longer receive its messages.
How the engine computer detects it
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.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
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
- Secondary ECM unpowered Most likely
- CAN wiring to secondary ECM broken Possible
- Gateway module routing CAN messages incorrectly Less likely
How to diagnose U0115
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: ecm, can bus wiring.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- U
- Network
- 0
- Generic (SAE) code
- 115
- Specific fault
Questions drivers ask
Can I drive with code U0115?
It depends on which module stopped communicating. If the car drives normally, drive carefully to a shop. If the engine, transmission, brakes or steering act up, or many warning lights come on at once, stop and have it towed.
Will my car pass an emissions inspection with U0115?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.