Remove the driver's or passenger's seat.

Disconnect the 3P connector (A) and 2P connector (B) from the seat heater.

Check for continuity between the B1 and B2 terminals of the seat-back heater 2P connector. There should be continuity.

Reconnect the 2P connector. Check for continuity between the A1 and A2 terminals, the A2 and A3 terminals, and the A1 and A3 terminals. There should be continuity.

If the continuity is not as specified, replace the appropriate seat heater.