OBD-II Diagnostic Trouble Code
U0029 — Vehicle Communication Bus B
U0029 sets when the module detects a fault on Vehicle Communication Bus B, an OEM-defined network separate from bus A. It indicates a general bus-level problem such as loss of valid traffic, not one specific module. The protocol, the modules on bus B and even the exact code definition vary by manufacturer, so confirm with service information.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Vehicle Communication Bus B
Code
U0029
Category
Network
Subsystem
Network
Truck-relevant
Yes
What this means for truckers
U0029 (Vehicle Bus B) — vehicle bus B segment fault.
Before you replace parts — try this first
U0029 on the Network system is most often wiring damage or corroded terminals on bus 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
Stored U-codes in several modules, inoperative features on that bus, intermittent warning lamps or cluster messages. Driveability is usually normal unless engine or transmission data depends on bus B.
Common causes
- CommonWiring damage or corroded terminals on bus B ($150–$800)
- CommonLow voltage or poor ground at modules on the bus ($100–$500)
- OccasionalInternal short in a module on bus B ($400–$2000)
- RareFaulty gateway module ($600–$1800)
How to fix
Look up which modules share bus B and check which ones are not responding
When to use: To narrow the fault area
Check module power, ground and fuses
When to use: Early in diagnosis, especially after battery work
Measure bus resistance and voltage and repair any open or short
When to use: When bus integrity tests fail
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 U0029?
U0029 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 U0029 on a commercial truck?
Total repair cost ranges $100–$2000 depending on the root cause. The cheapest fix is usually the first one listed below — Wiring damage or corroded terminals on bus 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 U0029 fail a DOT inspection?
U0029 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 U0029 and related codes?
U0029 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 U0029 is set without the companions, the issue is more isolated.
How do I prevent U0029 from coming back after a repair?
For U0029 (Vehicle Communication Bus 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.