OBD-II Diagnostic Trouble Code
U2105 — CAN Bus ECM Communication Error
U2105 is a manufacturer-specific code that, in its most common use, means a CAN bus communication error with the engine controller, meaning expected engine messages were not received correctly. Its exact definition varies by manufacturer, so check the OEM service information. It acts much like a lost-communication code for the engine controller.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
CAN Bus ECM Communication Error
Code
U2105
Category
Network
Subsystem
Network
Truck-relevant
Yes
What this means for truckers
U2105 (CAN Bus ECM Communication Error) — bus reports communication error from ECM perspective. Diagnose CAN wiring at ECM.
Before you replace parts — try this first
U2105 on the Network system is most often engine controller power, fuse or ground fault — 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
Multiple warning lamps, gauges dropping out, transmission limp mode, possible stall or no-start, and other U-codes stored together.
Common causes
- CommonEngine controller power, fuse or ground fault ($50–$300)
- CommonCAN wiring or connector damage at the engine controller ($150–$700)
- OccasionalLow battery voltage ($100–$700)
- RareEngine controller failure ($1000–$3500)
How to fix
Check batteries, engine controller fuses, power and grounds
When to use: First step
Check CAN bus voltage and termination resistance and inspect engine controller connectors
When to use: When power is good
Look up the OEM definition and any service bulletins
When to use: To confirm what the code means on this vehicle
Replace and program the engine controller
When to use: After other causes are ruled out
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
Frequently Asked Questions
Can I drive with code U2105?
U2105 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix U2105 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 — Engine controller power, fuse or ground fault — 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 U2105 fail a DOT inspection?
U2105 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 U2105 and related codes?
U2105 is closely related to: U2100 (Initial Configuration Not Complete), U2106 (CAN Bus TCM Communication Error), U2108 (CAN Bus ABS Communication Error). 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 U2105 is set without the companions, the issue is more isolated.
How do I prevent U2105 from coming back after a repair?
For U2105 (CAN Bus ECM Communication Error), 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.