OBD-II trouble code
U0115: Lost Communication with ECM/PCM B
A module on the network can no longer hear from the second engine/powertrain control module (ECM/PCM B). Usually a power, ground, or wiring fault — and because this module helps run the powertrain, the engine may run poorly, lose power, or fail to start.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $100 – $1,500
- DIY difficulty
- Shop recommended
What does U0115 mean?
U0115 is set when another module on the vehicle's communication network stops receiving messages from ECM/PCM B — the second engine or powertrain control module. Some vehicles use more than one powertrain controller: a second ECM/PCM may manage one cylinder bank, a second engine, or a portion of the powertrain control split between modules, and it shares data with the primary controller over the network. When the network loses contact with ECM/PCM B, U0115 records the dropout.
The causes follow the familiar communication-code pattern. The module may have lost power or ground through a blown fuse, corroded ground, or failed relay. The CAN wiring or connector at the module can be damaged or corroded, often from engine-bay heat, vibration, or fluid exposure. The module's internal communication circuitry can fail, or another module on the bus can disrupt communication for everyone. Low system voltage from a weak battery or charging fault can also cause intermittent dropouts.
Because powertrain control depends on this module, the symptoms are usually significant. The engine may run rough, misfire, lose power, hesitate, or fail to start, and the transmission may behave abnormally if shifting decisions rely on shared data. The check engine light comes on, typically with companion driveability or misfire codes. An engine that can't be controlled reliably is both a driveability and a safety concern — it may stall without warning — so U0115 warrants prompt diagnosis rather than continued driving.
Common causes
- Blown power or ground fuse for ECM/PCM B
- Corroded or loose ground at the module
- Damaged CAN wiring to ECM/PCM B
- Corroded or backed-out terminals at the module connector
- Engine-bay heat, vibration, or fluid exposure damaging wiring
- Failed internal communication circuitry in the module
- Another module on the bus disrupting network communication
- Low system voltage from a weak battery or charging fault
Symptoms
- Rough running, misfire, or noticeable power loss
- Hard starting or a no-start condition
- Engine stalls or hesitates under load
- Abnormal shifting if the transmission relies on shared data
- Check engine light on, often with driveability or misfire codes
- Scan tool can't communicate with ECM/PCM B specifically
- Symptoms may be intermittent with a marginal connection
Diagnostic steps
- 1.Scan all modules; confirm ECM/PCM B is the one that's unreachable while others respond.
- 2.Check the module's power and ground fuses and the relevant relays.
- 3.Inspect the module ground point and connector for corrosion, looseness, heat damage, and fluid intrusion.
- 4.Measure CAN-High and CAN-Low at the module connector (rest near 2.5 volts) and verify continuity back to the bus.
- 5.Test the battery and charging system, since low voltage can cause intermittent communication loss.
- 6.If power, ground, and wiring are good but the module still won't communicate, the module itself is the likely failure and will need replacement and programming.
Repair cost
$100 – $1,500
A blown fuse, corroded ground, or connector repair is the cheapest fix at $100-$300 once located. Wiring repair runs $200-$600. Diagnostic time commonly adds $150-$300. Replacing ECM/PCM B is the most expensive outcome at $500-$1,500 including programming, and is a last resort after cheaper causes are ruled out. Costs rise when the module must be programmed to the specific vehicle.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.