B29C2

Code

Generic B — Body

Gateway Module: CAN Bus Message Missing

Brand: Generic

Type: B — Body

Views: UK: 8 EN: 15 RU: 12

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Page language: EN

Causes

Failed or powered-off control module (node) that sends the message
Open, shorted, damaged or corroded CAN wiring or connector(s)
Faulty CAN transceiver in either the gateway or the sender module
Missing or incorrect termination (open or wrong resistance)
Loss of power or ground to the sender module or gateway
Module software mismatch, corrupted firmware or configuration error

Symptoms

Loss of function for systems that rely on the missing message (e.g., instrument cluster items, body functions, driver aids)
Intermittent or permanent module communication faults visible on a scan tool
Related diagnostic trouble codes for lost communication (other modules report 'no response')
Possible failure to start or accessory functions if essential messages are missing
No obvious mechanical fault — primarily electrical/communication symptoms

What to check

Read all codes and module status with a capable scan tool; note which message or module ID is reported missing
Check for additional U/B-type communication codes that help localize the network problem
Visually inspect CAN_H and CAN_L wiring, connectors, and module grounds/power feeds for damage or corrosion
Measure CAN bus termination resistance (expected ~60 ohms between CAN_H and CAN_L with ignition off and connectors connected)
Check for expected module battery/ignition power and good ground at the sender and gateway modules
Perform a wiggle test on wiring/connectors while monitoring for message appearance or new faults

Signal parameters

Idle voltages (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both idle near mid-supply)
Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V during dominant bits)
Typical total bus termination: ≈ 60 Ω measured between CAN_H and CAN_L (two 120 Ω terminators in parallel)
Common bit rates: 125 kb/s, 250 kb/s, 500 kb/s (confirm vehicle-specific bus speed before interpreting captures)
Expected message timing: depends on signal — many periodic messages occur every 10–100 ms; check wiring diagrams/SWFS for expected period

Diagnostic algorithm

Retrieve and record all DTCs and freeze frame data from all network modules; identify which module/message ID is missing.
Confirm the gateway and the reported sender module are present on the network with a scan tool. Note any 'no response' modules.
Inspect connectors, pins and harnesses for the gateway and sender module. Repair any corrosion, bent pins, or loose terminals.
Verify battery/ignition power and ground at both gateway and sender module. Repair power/ground faults before continuing.
With ignition ON, measure termination resistance between CAN_H and CAN_L (expect ~60 Ω). If out of range, locate and repair missing/bad terminator.
Use an oscilloscope or high-speed CAN tool to observe CAN_H and CAN_L at the gateway and near the sender. Look for missing frames, constant recessive levels, or severe noise/reflections.
If messages are present at one end of the bus but not at the gateway, trace wiring between those points for opens/shorts and perform continuity checks with power off.
Isolate sections by disconnecting branches or individual modules and re-check the bus to find where the message disappears or reappears.
If wiring and power/ground are good but the sender module does not transmit, attempt to re-initialize, wake, or cycle power to the module. If available, reflashing or reprogramming software per manufacturer procedure may be required.
If a hardware fault is suspected in a module (gateway or sender), substitute a known-good module or module bench test if possible, then clear codes and verify restoration of messages/functions.
After repairs, clear codes and perform functional test drive or operation to confirm the missing message does not recur.

Likely causes

Loose, corroded or disconnected connector at the gateway or sender module
Loss of power/ground to the sending module
Failed/removed sender module (module not responding)
Damaged CAN pair wiring (open or short to ground/voltage)
Faulty CAN transceiver or gateway hardware failure

Fault status

⚠️ Status

Gateway reports that a specific CAN message from another module was not received within the expected time window; network communication fault detected.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours