OBD-II Diagnostic Trouble Code
U0042 — High Speed CAN Communication Bus E
U0042 reports a fault on High Speed CAN Communication Bus E, one of the additional high-speed CAN networks used on vehicles with multiple segmented networks. The reporting module saw that bus fail to carry valid messages. Which modules use bus E is manufacturer specific.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
High Speed CAN Communication Bus E
Code
U0042
Category
Network
Subsystem
Network
Truck-relevant
Yes
What this means for truckers
U0042 (High Speed CAN Bus E) — fifth CAN segment fault (rare).
Before you replace parts — try this first
U0042 on the Network system is most often open or shorted bus e wiring or connector — 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
Lost-communication codes in modules on bus E, possible warning lamps, and loss of function of systems on that network. Depending on the bus, the truck may enter a reduced-power mode or simply show a warning.
Common causes
- CommonOpen or shorted bus E wiring or connector ($150–$800)
- CommonLow voltage or bad grounds ($100–$500)
- OccasionalModule on bus E with internal short ($500–$2000)
- RareGateway module failure ($600–$1800)
How to fix
Confirm bus E module list and terminator locations in OEM information
When to use: Before testing
Measure bus resistance (around 60 ohms typical with both terminators) and bus voltages
When to use: To find opens or shorts
Disconnect modules one at a time to isolate a bus-loading module
When to use: When wiring checks good but bus stays down
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 U0042?
U0042 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 U0042 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 — Open or shorted bus E wiring or connector — 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 U0042 fail a DOT inspection?
U0042 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 U0042 and related codes?
U0042 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 U0042 is set without the companions, the issue is more isolated.
How do I prevent U0042 from coming back after a repair?
For U0042 (High Speed CAN Communication Bus E), 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.