U0010

Code

Generic U — Network/User

Medium Speed CAN Communication Bus

Brand: Generic

Type: U — Network/User

Views: UK: 35 EN: 167 RU: 71

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or short in CANH or CANL wiring
Corroded or loose connectors or pins on CAN network
Missing or faulty termination resistor(s)
Faulty CAN transceiver in one or more modules
Module with internal failure pulling the bus to a voltage
Power or ground fault to a module on the medium-speed CAN bus

Symptoms

Malfunction Indicator Lamp (MIL) or other warning lights illuminated
Loss of function for systems on the medium-speed CAN (e.g., instrument cluster, body systems, gateway functions)
Intermittent or permanent communication errors in scan tool live data
Other modules report lost communication or set related U-codes
Features controlled via that bus may be inoperative or intermittent

What to check

Connect a full-function scan tool; record active and historic U-codes and related module communication status
Visually inspect CAN wiring, connectors, and modules for corrosion, damage, pin push-outs, or moisture
Check for other related codes on modules attached to the medium-speed CAN
Measure resistance between CANH and CANL with ignition off and battery disconnected (expected ~60Ω for a two-terminator system; varies by design)
With key ON (engine off) measure CANH and CANL voltages to reference ground at a good node
Wiggle-test wiring and connectors while monitoring bus status with scan tool or oscilloscope to reproduce fault

Signal parameters

Idle common-mode voltage (CANH ≈ 2.5 V, CANL ≈ 2.5 V)
Dominant state voltages: CANH ≈ 3.5 V, CANL ≈ 1.5 V (differential ≈ 2.0 V)
Recessive state: both CANH and CANL ≈ 2.5 V (differential ≈ 0 V)
Line resistance across CANH–CANL ≈ 60 Ω (typical two 120 Ω terminators in parallel)
Bit rates commonly used on medium-speed CAN: 125 kbps or 250 kbps (verify vehicle spec)
Common-mode voltage should remain within module specification (typically within 0–5 V); persistent out-of-range indicates short or power issue

Diagnostic algorithm

Connect scan tool and note all U-codes and affected modules; check freeze frame and time stamps
Perform visual inspection of harness, splices, and connectors serving the medium-speed CAN; repair obvious damage
Verify module power and ground circuits for proper voltage and resistance; repair any supply or ground faults
Measure resistance between CANH and CANL with ignition off; compare to expected value for that vehicle (commonly ~60 Ω). If open or shorted, trace wiring for opens/shorts
With key ON (engine off) measure CANH and CANL voltages at a known-good node. If voltages are stuck high/low or show short to supply/ground, isolate and find shorted module or wiring
Use an oscilloscope to inspect waveform at multiple nodes while operating the bus; look for missing transitions, dominant-stuck, reflections, or noise
Perform a module isolation test: disconnect suspected modules one at a time (following safe manufacturer procedures) to see when the fault clears
If a single module is identified as causing the fault, verify by replacing or bench-testing transceiver or module per service information
Replace/repair wiring, connectors, terminators or modules as identified; restore any damaged insulation and protect connectors from moisture
Clear codes, perform relearns or module programming if required, and road test to confirm repair and that codes do not return

Likely causes

Damaged wiring or connector at a harness splice or module connector
Failed CAN transceiver in a module (common after water ingress)
Missing/failed termination resistor (open or changed value)
Low or missing power/ground to a module causing it to hold the bus in a dominant state

Fault status

⚠️ Status

U0010 — Medium Speed CAN Communication Bus: indicates loss of or abnormal communication on the vehicle’s medium-speed CAN network. Modules on that bus are not communicating properly; check wiring, termination, module transceivers, and power/ground.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours