B12AC Code: Meaning, Causes, and Symptoms | OBD2 Codes

B12AC – Drivers Heated Seat Relay Drive Circuit Open Or Shorted to Ground

 

B12AC Possible Symptoms

 

Engine Light ON (or Service Engine Soon Warning Light)

 

B12AC Possible Causes

 

Faulty Heater Seat Relay,Faulty Heater Mat,Heater Mat harness is open or shorted,Heater Mat circuit poor electrical connection,Faulty Heating, Ventilation, and Air-Conditioning (HVAC) Module

 

B12AC Description

 

The Heating, Ventilation, and Air-Conditioning (HVAC) Module contains the driver heated seat control button and indicator. The heated seat system functions independently from the climate control system. A heated seat relay is located underneath the driver seat cushion frame. There are 2 voltage supplies to the heated seat relay. Voltage is supplied from the Smart Junction Box (SJB) heated seat relay enable circuit to the driver heated seat relay coil when the engine is running. Ground is supplied to the opposite side of the driver relay coil by the HVAC module driver heated seat relay drive circuit when the driver heated seat switch button is pressed to energize the relay. This closes the relay contacts to supply battery voltage from the SJB circuit to the driver heater mat circuit. The driver heater mats are directly connected to ground circuit completing the electrical circuit to heat the seat.