Heated Seats don’t work — Chevrolet

Diagnose and fix heated seats don’t work condition

Every car maker has their own scheme for how they run their heated seats. The system I’ll describe here is for many Chevrolet heated seats don’t work issues. This also applies to other GM vehicles like Buick, Cadillac, GMC and Pontiac.

Heated Seat Components

GM heated seat systems for vehicle produced from early 2000 thru late 2000 include

Driver and passenger side heated seat control switches

Driver and passenger side seat back heating elements

Driver and passenger side seat cushion heater elements

Driver and passenger side seat back temperature sensors

Driver seat module

Driver door control module

Passenger door control module

Passenger seat module

How Chevrolet heated seats work

GM designed the system to have 2 heat zones with 3 heat levels. The buttons refer to the heaters in the seat cushion or the seat back. If the driver presses the seat cushion button, it  activates the heaters in both the seat cushion and seat back. However, if the driver presses the seat back button, only the seat back heater will activate.

Three heated seat heating levels

The heat level is determined by the number of times the seat cushion and back or back buttons are pressed. Pressing the seat cushion 1 time activates both the seat back and cushion heater elements to run in the high heat mode. Subsequent button presses of the same button reduce the heat level from high to medium, medium to low, and low to off. The same routine applies to the seat back button; first press is high, while subsequent presses reduce the heat level.

How buttons control heated seats

The door modules receive battery power from a door circuit breaker (25A) and a driver/passenger door module fuse (15A) located in the left instrument panel fuse box. The door modules then provide power to each heated seat switch and each button press produces a momentary contact closure. The door module sees the contact closure requesting heat and heat level and communicates the request to the seat module via a digital bus.

The heated seat wiring diagram shows the schematic for one seat. The wiring diagram for the other seat is the same

The seat module receives battery power from the seat circuit breaker (30A); one for each seat located in the instrument panel relay block. The seat module provides power and ground to the seat and back heating elements. The seat module controls which heating element is activated by switch the appropriate heating element ground on or off. In addition to controlling which heating element is activated, the seat module controls the heat level by switching the ground on or off. It determines when to perform the switching based on temperature feedback from the 2-wire thermistor located near the seat back element. The thermistor receives a 5-volt reference from the seat module and the module notes the varying voltage drop from each thermistor based on the temperature it senses.

Heated seats don’t work — How to test

Check fuses (1)

Check for battery power at door module (2)

Check for battery power at seat module (3)

Check for good ground at door module (4)

Check for good ground at seat module (5)

Check for power at back switch (6)

Check for power at back and seat switch (7)

Disconnect electrical connectors from seat module to heater elements and test

Seat thermistor continuity (set meter to ohms scale). Resistance should be 10KΩ ± 2KΩ at room temperature. If meter reads OL or ∞ the seat thermistor is open and must be replaced.

Next, check heater element resistance. Set meter to ohms. Resistance should be 1.5-5.5Ω. If meter reads OL or ∞ the element is open and must be replaced. Double check the heater element by jumpering a light bulb (#3056 or 194) in place of the seat or back heating element. Activate the seat heater and see if the light comes on with the bulb in place. If the light comes on now but didn’t when the actual heating element was connected, this test confirms the element is bad and must be replaced.

©, 2020 Rick Muscoplat