U0278

Code

Generic U — Network/User

Lost Communication With Seat Control Module L

Brand: Generic

Type: U — Network/User

Views: UK: 21 EN: 40 RU: 23

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or short in CAN (or LIN) data lines to seat module
Poor or missing power supply (fuse, ignition feed) to seat module
Poor ground or corroded connector at seat module
Faulty Seat Control Module (internal failure)
Connector pin damage or corrosion from seat movement
Network termination or wiring splice fault

Symptoms

Left seat power adjustments do not work (fore/aft, recline, lumbar)
Seat heater/vent or memory functions for left seat inoperative
Driver information message or indicator for seat module communication fault
Multiple related DTCs or body module errors
Intermittent operation or loss of seat functions when seat is moved

What to check

Connect an advanced scan tool and read all U-codes and module network status; record freeze frame and occurrence conditions
Verify battery voltage and stable system voltage (12.0–14.5 V) with ignition ON
Inspect fuses and relays related to seat power and modules
Visually inspect seat harness, connectors, and pins for corrosion, damage, or broken wires (pay attention to harness areas that flex)
Check for other modules reporting bus errors or Bus‑Off conditions
Backprobe seat module connector: verify key‑on 12 V power, good ground, and any wake lines (if LIN)

Signal parameters

Normal CAN idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each) with ≈ 0 V differential when idle
Dominant (logic 0) state typical voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Termination: expected resistance between CAN_H and CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel)
Typical CAN bus speeds for body networks: commonly 250 kbps or 500 kbps (verify vehicle specification)
Module power: key‑on battery voltage ≈ 12 V; ground near 0 V; LIN (if used) typically 0–12 V signaling depending on implementation

Diagnostic algorithm

Use scan tool: read all codes, note U0278 confirmation count and any related U or B codes. Check module list to see if Seat Control Module L appears.
Check vehicle battery voltage and charge if low. Verify fuses/relays for seat module power circuits; replace any blown fuses.
Perform visual inspection: open seat trim as required, inspect left seat harness, connectors, and pin terminals for damage, corrosion, or chafing points (hinge/track areas). Repair any visible wiring damage.
Backprobe the seat module connector: verify constant/keyed 12 V power and ground presence. If power or ground missing, trace and repair feed or ground connection.
Measure CAN_H/CAN_L at the seat module connector with DMM or scope: compare to expected signal parameters. If voltages are out of range, isolate wiring for shorts to battery/ground.
Check termination resistance between CAN_H and CAN_L at module connector; if not near expected, inspect network terminators and connectors.
Wiggle the harness and move the seat through full travel while monitoring live data and DTCs to reproduce intermittent faults.
If wiring and power/ground are good and CAN signals look healthy but module does not respond, attempt to clear codes and power‑cycle. If code returns, consider reprogramming or replacement of the seat control module per manufacturer procedure.
After repair or module replacement, clear codes and verify communication and seat function. Perform any required calibration or coding for new modules.
If multiple modules report network faults or bus‑off, diagnose the gateway or other modules that may be pulling the bus down; use a CAN analyzer if necessary.

Likely causes

Damaged wiring or connector in the left seat harness (most likely due to seat movement)
Blown fuse or missing battery/ignition feed to the seat module
Corroded connector or poor ground at the seat module
Faulty seat control module
CAN bus short or missing termination causing module not to be seen

Fault status

⚠️ Status

Stored when the Seat Control Module L does not respond to network messages or is not detected on the vehicle communication bus. Can be intermittent or permanent; additional related U codes or local seat DTCs may be present.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.5 hours

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