OBD-II Diagnostic Trouble Code
U0115 — Lost Communication With ECM/PCM B
U0115 means a module lost communication with ECM/PCM B, a second engine or powertrain controller used on some vehicles alongside the primary ECM. On some diesel and hybrid systems this is a secondary engine or aftertreatment controller. Exact role depends on the OEM.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Lost Communication With ECM/PCM B
Code
U0115
Category
Network
Subsystem
Network
Truck-relevant
Yes
What this means for truckers
U0115 (Lost Communication With ECM/PCM B) — on dual-ECM systems (rare in commercial — mostly some Ford SuperDuty), the secondary ECM is offline. Diagnose ground and CAN wiring.
Before you replace parts — try this first
U0115 on the Network system is most often power, ground or fuse fault at ecm b — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Warning lamps, possible derate or reduced engine function, aftertreatment or emissions faults, and in some cases a no-start. Symptoms depend on what ECM B controls.
Common causes
- CommonPower, ground or fuse fault at ECM B ($50–$400)
- CommonNetwork wiring or connector fault ($150–$800)
- OccasionalLow battery voltage ($100–$500)
- RareFailed ECM B ($1200–$3500)
How to fix
Identify ECM B for the truck and check its power, grounds and fuses
When to use: First step
Inspect and test the network wiring to ECM B
When to use: When power is good
Replace and program ECM B
When to use: When power and wiring are good but it does not communicate
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → U0100 — Lost Communication With ECM/PCM A
- → U0101 — Lost Communication With TCM
- → U0102 — Lost Communication With Transfer Case Control Module
- → U0103 — Lost Communication With Gear Shift Module
- → U0104 — Lost Communication With Cruise Control Module
Frequently Asked Questions
Can I drive with code U0115?
Drive with caution. U0115 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix U0115 on a commercial truck?
Total repair cost ranges $50–$3500 depending on the root cause. The cheapest fix is usually the first one listed below — Power, ground or fuse fault at ECM B — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will U0115 fail a DOT inspection?
U0115 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between U0115 and related codes?
U0115 is closely related to: U0100 (Lost Communication With ECM/PCM A), U0101 (Lost Communication With TCM), U0102 (Lost Communication With Transfer Case Control Module), U0103 (Lost Communication With Gear Shift Module). These codes share the same subsystem (network) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only U0115 is set without the companions, the issue is more isolated.
How do I prevent U0115 from coming back after a repair?
For U0115 (Lost Communication With ECM/PCM B), prevention centers on the network system. Pay attention to ground connections at every PM — bad grounds are 70% of communication codes. Inspect harness routing for chafe points. Don't disconnect modules with the key on.