U2600

Code

Generic U — Network/User

Invalid CAN communication received

Brand: Generic

Type: U — Network/User

Views: UK: 19 EN: 20 RU: 13

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Damaged or corroded CAN wiring or connectors
Failed CAN transceiver in a control module
Incorrect or mismatched module software/configuration on the bus
Missing or incorrect termination resistors (open/shorted termination)
Electrical interference (EMI) or high bus load causing bit errors
Loose or poor ground or power supply to one or more modules

Symptoms

MIL (check engine) or warning lamp(s) illuminated
Intermittent or permanent loss of functionality for one or more modules or subsystems
Erratic instrument cluster readings or switched functions
Stored communication-related DTCs in one or more modules
Modules showing as offline or not responding to diagnostic tool
Network-related fault flags such as bus-off in ECU error counters

What to check

Read all modules and record all stored and pending DTCs and freeze-frame data
Visually inspect CAN wiring, connectors and grounds for damage, corrosion, loose pins or aftermarket splices
Confirm vehicle history: recent module replacements, software updates, or accessory installations
Measure termination resistance between CAN_H and CAN_L at key harness connectors (expect ~60 Ω with two 120 Ω terminators)
Use a scan tool to monitor CAN bus traffic and note missing, malformed, or abnormally timed frames
Check battery and module supply/ground voltages for stability

Signal parameters

Idle (recessive) voltage: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each)
Dominant state voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Expected bus bit rates: commonly 125 kb/s, 250 kb/s, 500 kb/s, 1 Mb/s — verify correct baud for vehicle
Differential voltage between CAN_H and CAN_L (dominant ≈ 2.0 V, recessive ≈ 0 V)
Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω in parallel)
Error counters/TEC/REC and bus-off counts from affected modules

Diagnostic algorithm

Retrieve and document all stored/pending U- and P-codes and freeze-frame data from every module on the network.
Note recent service or accessory work that could have introduced wiring changes or replacement modules.
Visually inspect CAN_H/CAN_L wiring, connectors and module pins for damage, corrosion, bent pins or aftermarket splices; repair any issues found.
With ignition off, measure termination resistance between CAN_H and CAN_L at diagnostic connector or harness — expect ≈60 Ω. If open or low, trace and repair termination.
With a bidirectional scan tool, monitor live CAN traffic while exercising affected functions; identify missing or malformed frames and which node/transmit ID is associated.
Probe CAN_H and CAN_L with an oscilloscope (or CAN bus analyzer). Verify proper recessive/dominant voltages, clean edges, correct bit timing, and absence of repeated bit errors or distortions.
Isolate the network segment: disconnect suspect modules or aftermarket devices one at a time while monitoring bus quality to locate the node causing invalid frames.
If a suspect module is identified, check its supply and ground, re-seat connectors, update or reflash module software if available, or replace module/transceiver per manufacturer guidance.
After repair, clear all codes, re-run communication checks, and road-test while monitoring CAN traffic to confirm no recurrence.
If fault persists and root cause cannot be isolated, escalate to manufacturer-specific diagnostics or specialist with OEM-level tools.

Likely causes

Wiring harness damage, chafing, or poor connector pin contact on CAN_H/CAN_L
Faulty CAN transceiver on a control module causing malformed frames
Incorrect termination (open or shorted 120 Ω resistors) or additional unintended termination
Software mismatch or corrupted firmware in a recently replaced/updated module
Intermittent ground or supply voltage to a module causing corrupted transmissions