U0209

Code

Generic U — Network/User

Lost Communication With Seat Control Module B

Brand: Generic

Type: U — Network/User

Views: UK: 26 EN: 42 RU: 27

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Page language: EN

Seat functions inoperative or intermittent (adjustment, memory, heating/ventilation, lumbar)
Related modules report seat-related faults or reduced features
Stored U0209 and possibly other communication codes
Possible illumination of generic warning lamp or message on dash
Seat position not saved or recalled

Use a scan tool to confirm U0209, note freeze-frame and any simultaneous communication codes
Check for additional related DTCs (other U01xx/U02xx or module-specific codes)
Visually inspect seat module connector for corrosion, bent pins, water, or damage
Verify fuses and relays supplying the seat control module
Backprobe and measure key power and ground circuits at the module
Check CAN/LIN bus voltages at the seat module connector with key on

CAN bus recessive voltage: each line typically near 2.5 V (both lines equal)
CAN dominant state: CAN_H ~3.5 V and CAN_L ~1.5 V (differential ~1.5–2.0 V)
CAN termination resistance: ~60 ohms across CAN_H and CAN_L (two 120 Ω in parallel)
LIN bus idle: typically pulled high to battery voltage via resistor (varies by manufacturer)
Expected: seat control module should appear on network and respond to periodic messages/ID; absence indicates lost communication

Connect an OEM-capable scan tool. Record U0209 and any other network codes, note freeze-frame data and timestamps.
Attempt to communicate with Seat Control Module B via scan tool. If no response, attempt a module present/ID request if allowed.
Visually inspect module connector and harness for corrosion, damage, or water intrusion. Repair as needed.
Verify fuse(s) and measure battery voltage at the module's power pin with ignition on. Confirm a good ground at module ground pin.
With ignition on, measure CAN_H and CAN_L voltages at the module connector. Compare to expected values. If voltages abnormal, isolate wiring to nearest junction or gateway.
Check continuity and shorts: measure resistance between CAN_H and CAN_L (terminals disconnected) and check for shorts to battery and ground.
Inspect/measure termination resistors near gateway/BCM. Replace or repair if termination missing or incorrect.
If wiring and power/ground are good but no communication, try swapping with a known good seat module (if available) or substitute known-good gateway/BCM only when guided by OEM procedures.
Reprogram or reflash module software per OEM instructions if module responds but shows software faults.
Clear codes and perform function test. Monitor for reoccurrence and verify related seat functions operate normally.