OBD-II Diagnostic Trouble Code
U0073 — Control Module Communication Bus Off
U0073 means the reporting module's CAN controller went into a bus-off state on communication bus A, usually the main high-speed CAN. Bus-off happens when the controller counts too many transmit errors and disconnects itself to protect the network. It points to a bus wiring problem, a noisy or shorted bus, or the module's own transceiver.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Control Module Communication Bus Off
Code
U0073
Category
Network
Subsystem
Network
Truck-relevant
Yes
What this means for truckers
U0073 — see existing entry.
Before you replace parts — try this first
U0073 on the Network system is most often can high or low shorted to ground, power or each other — 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
Can range from a warning lamp only to no-start, derate, loss of cruise, dead gauges or inability to communicate with a scan tool, depending on which modules lose data. Many modules may log lost-communication codes at the same time.
Common causes
- CommonCAN high or low shorted to ground, power or each other ($150–$800)
- CommonCorroded or loose connector at a module or splice pack ($100–$500)
- OccasionalFaulty module transceiver flooding or corrupting the bus ($500–$2500)
- OccasionalMissing or failed terminating resistor ($100–$400)
- OccasionalLow or unstable system voltage during cranking ($100–$500)
How to fix
Measure CAN high and low to ground and to each other with key off and on
When to use: To locate shorts and confirm termination
Inspect splice packs and module connectors for corrosion, especially near the frame and engine
When to use: When the fault is intermittent or after weather exposure
Disconnect modules one by one until the bus recovers
When to use: When wiring checks good but bus-off returns
Replace the reporting module only after bus and power checks pass
When to use: When only that module goes bus-off and others communicate normally
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
- → U0001 — High Speed CAN Communication Bus
- → U0002 — High Speed CAN Communication Bus Performance
- → U0010 — Medium Speed CAN Communication Bus
- → U0019 — Medium Speed CAN Communication Bus B
- → U007A — Control Module Communication Bus H Off
Frequently Asked Questions
Can I drive with code U0073?
U0073 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 U0073 on a commercial truck?
Total repair cost ranges $100–$2500 depending on the root cause. The cheapest fix is usually the first one listed below — CAN high or low shorted to ground, power or each other — 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 U0073 fail a DOT inspection?
U0073 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 U0073 and related codes?
U0073 is closely related to: U0001 (High Speed CAN Communication Bus), U0002 (High Speed CAN Communication Bus Performance), U0010 (Medium Speed CAN Communication Bus), U0019 (Medium Speed CAN Communication Bus B). 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 U0073 is set without the companions, the issue is more isolated.
How do I prevent U0073 from coming back after a repair?
For U0073 (Control Module Communication Bus Off), 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.