Seat Temperature Relay: Description and Operation

Fig.6 Heated Seat Relay:

The heated seat relay is located on the power seat track front bracket under the front edge of the right front seat cushion, where it is secured with a push-in type plastic fastener. The heated seat relay is a conventional International Standards Organization (ISO) mini relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The relay is contained within a small, rectangular, molded plastic housing with an extended skirt that serves as the connector receptacle. The relay is connected to all of the required inputs and outputs through the power seat wire harness by five male spade-type terminals that extend from the bottom of the relay base. The ISO designation for each terminal is molded into the base adjacent to each terminal. The ISO terminal designations are as follows:
- 30 (Common Feed) - This terminal is connected to the movable contact point of the relay.
- 85 (Coil Ground) - This terminal is connected to the ground feed side of the relay control coil.
- 86 (Coil Battery) - This terminal is connected to the battery feed side of the relay control coil.
- 87 (Normally Open) - This terminal is connected to the normally open fixed contact point of the relay.
- 87A (Normally Closed) - This terminal is connected to the normally closed fixed contact point of the relay.

The heated seat relay cannot be adjusted or repaired. If the relay is damaged or faulty, it must be replaced.

The heated seat relay is an electromechanical switch that uses a low current input from the ignition switch to control the high current output to the heated seat module. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. The resistor or diode is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The heated seat relay terminals are connected to the vehicle electrical system through a connector and take out of the power seat wire harness. The inputs and outputs of the heated seat relay include:
- The common feed terminal (30) receives a battery current input from the power seat circuit breaker in the Junction Block (JB) through a fused B(+) circuit at all times.
- The coil ground terminal (85) receives a ground feed input at all times from a two wire take out and eyelet terminal connector of the power seat wire harness that is secured by a ground screw to the top of the seat crossmember under the right front seat.
- The coil battery terminal (86) receives a battery current input from a fuse in the JB through a fused ignition switch output (run-acc) circuit only when the ignition switch is in the ON or Accessory positions.
- The normally open terminal (87) provides a battery current output to the heated seat module (also known as the Seat Heat Interface Module or SHIM) through the heated seat relay output circuit only when the heated seat relay control coil is energized.
- The normally closed terminal (87A) is not connected to any circuit in this application, but battery current should be present at this terminal whenever the heated seat relay control coil is de-energized.