U0065

Code

Generic U — Network/User

Vehicle Communication Bus E Performance

Brand: Generic

Type: U — Network/User

Views: UK: 29 EN: 43 RU: 25

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open, short, or high-resistance wiring on Bus E (CAN high/low or equivalent)
Faulty or intermittent connector(s) at a module on Bus E
Failed control module on Bus E transmitting corrupted messages
Missing or incorrect bus termination (open or shorted termination resistor)
Low or unstable battery/ECU supply voltage affecting nodes on Bus E
Electromagnetic interference (aftermarket devices, poor routing)

Symptoms

Illuminated dash warning lights (CAN/communication, ABS, traction, check engine, etc.)
Loss or reduced functionality of one or more systems controlled by Bus E (e.g., ABS, traction, ADAS, body systems)
Multiple modules reporting 'Not Responding' or related U-codes
Intermittent or persistent drivability issues if propulsion modules affected
Stored or active communication-related DTCs in one or more modules

What to check

Read and record all U and manufacturer-specific codes from every control module with a capable scan tool
Check battery voltage and charging system; ensure stable supply (12.4–14.6 V as appropriate)
Visually inspect harnesses/connectors on modules attached to Bus E for damage, corrosion, or loose pins
Check for proper bus termination resistance (approximately 60 ohms across CAN H-L for two 120-ohm terminators in parallel; value depends on vehicle design)
Measure idle voltages on CAN high and CAN low relative to ground (~2.5 V each for CAN) and differential (~0 V at rest for LIN; adjust for bus type)
Use an oscilloscope to view bus waveform for noise, missing frames, dominant/recessive faults, or abnormal voltages

Signal parameters

CAN High idle voltage ≈ 2.5 V (relative to chassis ground) — varies slightly under load
CAN Low idle voltage ≈ 2.5 V (relative to chassis ground) — differential idle ≈ 0 V, differential dominant ≈ 2 V
Expected bus bit rate — commonly 125 kbps, 250 kbps, 500 kbps or 1 Mbps depending on vehicle (confirm manufacturer spec)
Bus termination resistance — typically ~60 ohms measured across CANH and CANL for a properly terminated 2-terminator CAN network
Bus error counters and frame error rate reported by scan tool (should be low/zero under normal conditions)
Message/message IDs and frequency for modules on Bus E — used to verify missing frames

Diagnostic algorithm

Retrieve and document all DTCs and freeze-frame data from all modules; note which modules report loss of communication.
Clear codes and attempt to reproduce; determine whether U0065 returns steady or intermittently.
Verify vehicle battery voltage and connections; charge or replace battery if low and re-check.
Visually inspect all connectors and wiring for modules on Bus E; repair obvious damage or corrosion.
Measure CANH/CANL voltages at multiple nodes with key ON, engine off; compare to expected values.
Measure termination resistance across CANH and CANL at key points; confirm proper termination present.
Use an oscilloscope to capture bus signals while attempting communication; look for noise, dominant states, missing frames, or a stuck node.
If a bad waveform or a stuck dominant state is found, systematically disconnect suspect modules (one at a time) to locate the faulty node causing bus errors.
Inspect and repair any short to battery/ground or open circuits found; replace damaged harness sections or connectors.
If a module is identified as the source (continues to cause errors when connected), follow manufacturer procedures to reprogram or replace the module.
After repairs, clear codes, verify communication restored to all modules, and perform any required relearn or initialization procedures.

Likely causes

Damaged harness or corroded connector on Bus E (most common)
Failed module driving the bus (transmitter transmitting invalid frames)
Missing or faulty termination resistor(s) at bus ends
Low vehicle battery or intermittent power/ground to a module
Aftermarket accessory injecting noise on the bus

Fault status

⚠️ Status

Communication Bus E Performance — messages on Bus E are missing, corrupted, or the bus is degraded. This indicates an issue with wiring, termination, a module on Bus E, or power/ground affecting communication.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-4 hours