U0278: Lost Communication With Seat Control Module L

What it means

The vehicle bus reports loss of communication with seat control module L. Power-seat positions, memory presets and heating/ventilation requests routed through this node are no longer answered.

How it works

Seat Control Module L operates the seat functions assigned to it, which can include power positioning, memory, heating, or ventilation. Other modules expect Module L to answer over the vehicle bus; this code sets when its messages are missing.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules for communication faults and save freeze-frame data to establish whether Module L alone is offline.
2. Test the seat positions, memory presets, and any heating or ventilation functions routed through Module L to identify what has stopped working.
3. Inspect Module L's connector and under-seat harness for loose connections, corrosion, pinched wires, or damage as the seat moves.
4. Verify Module L's power and ground according to the manufacturer's procedure.
5. Check the bus wiring to Module L for opens or shorts before considering module replacement.

Common fixes

• Reconnect a loose Module L plug and secure the wiring clear of the seat tracks.
• Repair damaged bus wiring under the seat.
• Repair the missing power or ground connection to Module L.
• Replace Module L if its supply and bus circuits test correctly but communication does not return.

Can I keep driving?

You can generally drive if the seat is firmly secured in a safe position, but lack of adjustment may prevent a suitable driving position. Do not drive with a seat that moves or will not lock.