OBD-II Diagnostic Trouble Code
U0030 — Vehicle Communication Bus B Performance
U0030 indicates a performance problem on Vehicle Communication Bus B: the bus is working but the module is seeing excessive errors, dropped frames or timing problems. This is different from a complete bus failure and often points to an intermittent or marginal fault. Bus B definition varies by OEM.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Vehicle Communication Bus B Performance
Code
U0030
Category
Network
Subsystem
Network
Truck-relevant
Yes
What this means for truckers
U0030 (Vehicle Bus B Performance) — bus performance degraded.
Before you replace parts — try this first
U0030 on the Network system is most often intermittent connector contact, pushed-back pins or corrosion — 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
Intermittent warning lights, gauges or accessories that flicker or drop out briefly, and U-codes that come and go. Often no driveability change; sometimes momentary loss of a feature while driving over rough roads.
Common causes
- CommonIntermittent connector contact, pushed-back pins or corrosion ($100–$500)
- OccasionalMarginal charging voltage or alternator ripple ($150–$700)
- OccasionalElectrical noise from aftermarket devices or damaged twisted-pair wiring ($75–$400)
- RareDegraded module transceiver causing bus errors ($400–$1800)
How to fix
Wiggle-test harness and connectors on bus B while monitoring communication
When to use: When the fault is intermittent
Check alternator output and AC ripple and verify grounds
When to use: When the code appears with charging or voltage complaints
Remove aftermarket devices tapped into the network and retest
When to use: When telematics or accessories were recently installed
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
- → U0073 — Control Module Communication Bus Off
- → U007A — Control Module Communication Bus H Off
Frequently Asked Questions
Can I drive with code U0030?
U0030 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 U0030 on a commercial truck?
Total repair cost ranges $75–$1800 depending on the root cause. The cheapest fix is usually the first one listed below — Intermittent connector contact, pushed-back pins or corrosion — 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 U0030 fail a DOT inspection?
U0030 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 U0030 and related codes?
U0030 is closely related to: U0001 (High Speed CAN Communication Bus), U0002 (High Speed CAN Communication Bus Performance), U0010 (Medium Speed CAN Communication Bus), U0073 (Control Module Communication Bus Off). 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 U0030 is set without the companions, the issue is more isolated.
How do I prevent U0030 from coming back after a repair?
For U0030 (Vehicle Communication Bus B Performance), 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.