I have seen a lot of heated seats not working threads lately. Here is the electrical schematic and diagnostic procedure to find out what is wrong from the GM service manual. I have the GM ESI software(Factory Service manuals) through model year 2005 for most GM model cars.



Service InformationHeated Seat Inoperative Monte Carlo

Step Action Values
Yes
No
Schematic Reference: Heated Seats Schematics

1
Did you perform the Power Seat Diagnostic System Check?
--
YES: Go to Step 2
NO: Go to Diagnostic System Check - Power Seat Systems
2

1. Start the engine.
2. Operate the heated seat switch in the LOW and HIGH positions.

Does the heated seat operate in low and high modes?
--
YES: Go to Testing for Intermittent and Poor Connections in Wiring Systems
NO: Go to Step 3
3
Do the LOW and HIGH switch indicators operate properly?
--
YES: Go to Step 6
NO: Go to Step 4
4
Important

The body control module (BCM) is programed to supply voltage to the heated seat switch only while the engine is running.

1. Disconnect the heated seat switch connector.
2. Connect a test lamp from the ignition voltage supply circuit terminal in the harness connector to a ground.

Does the test lamp illuminate?
--
YES: Go to Step 5
NO: Go to Step 17
5
Connect the test lamp from the ignition voltage supply circuit terminal to the ground circuit terminal in the heated seat switch harness connector.
Does the test lamp illuminate?
--
YES: Go to Step 22
NO: Go to Step 18
6

1. Using a test lamp backprobe the seat heater element supply circuit terminal in the heated seat relay connector.
2. Operate the heated seat switch in the HIGH position.

Does the test lamp illuminate?
--
YES: Go to Step 12
NO: Go to Step 7
7

1. Disconnect the heated seat relay.
2. Connect a test lamp from the heated seat switch signal circuit terminal in the harness connector to ground.
3. Operate the heated seat switch in the HIGH and LOW positions.

Does the test lamp illuminate in the HIGH and LOW switch positions?
--
YES: Go to Step 8
NO: Go to Step 15
8

1. Turn OFF the ignition.
2. Connect a test lamp from the battery positive voltage supply circuit terminal in the heated seat relay harness connector to ground.

Does the test lamp illuminate?
--
YES: Go to Step 9
NO: Go to Step 19
9
Connect a test lamp from the battery positive voltage supply circuit terminal to the ground circuit terminal in the heated seat relay harness connector.
Does the test lamp illuminate?
--
YES: Go to Step 10
NO: Go to Step 20
10
Test the resistance from the heated seat thermistor signal circuit terminal to the ground circuit terminal in the heated seat relay harness connector.
Is the resistance within the specified values?
7K-11K ohms
YES: Go to Step 11
NO: Go to Step 14
11

1. Measure the resistance through the heated seat switch from the heated seat switch signal circuit terminal to the heated seat switch high/low signal circuit terminal in the heated seat relay harness connector.
2. Operate the heated seat switch in the HIGH and LOW positions.

Is the resistance at or near the specified values?

• HIGH 310 ohms
• LOW 200 ohms

YES: Go to Step 27
No: Go to Step 16
12

1. Turn OFF the ignition.
2. Disconnect the seat cushion heater element 4-way connector.
3. Test the resistance through the seat cushion heater element.

Is the resistance within the specified values?
0.5-2 ohms
YES: Go to Step 13
No: Go to Step 25
13

1. Disconnect the seat back heater element 2-way connector.
2. Test the resistance through the seat back heater element.

Is the resistance within the specified values?
0.5-2 ohms
YES Go to Step 21
NO: Go to Step 26
14

1. Disconnect the seat cushion heater element 4-way connector.
2. Test the heated seat thermistor signal and ground circuits in the seat harness for the following conditions:
   • Open or high resistance
   • Short to ground
   • Short to battery positive voltage

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES: Go to Step 31
NO: Go to Step 24
15
Test the heated seat switch signal circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 31
Go to Step 22
16
Test the high/low switch signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES: Go to Step 31
NO: Go to Step 22
17
Test the ignition voltage supply circuit to the heated seat switch for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES: Go to Step 31
NO: Go to Step 29
18
Repair the open or high resistance in heated seat switch ground circuit. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
YES: Go to Step 31
--
19
Repair the open or short to ground in the battery positive voltage supply circuit to the heated seat relay. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
YES: Go to Step 31
--
20
Repair the open or high resistance in the seat heater control module ground circuit. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
YES Go to Step 31
--
21
Repair the open or short to ground in the heater element supply or ground circuits in the seat harness. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
YES: Go to Step 31
--
22
Inspect for poor connections at the heated seat switch. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES: Go to Step 31
NO: Go to Step 23
23
Replace the heated seat switch. Refer to Heated Seat Switch Replacement .
Is the repair complete?
--
YES: Go to Step 31
--
24
Inspect for poor connections at the seat cushion heater element. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES Go to Step 31
No: Go to Step 25
25

1. Replace the seat cushion heater element. Refer to Seat Heater Element Replacement - Front .
2. Operate the Heated Seat System.

Does the system operate normally?
--
YEs: Go to Step 31
NO: Go to Step 13
26
Replace the seat back heater element. Refer to Seat Heater Element Replacement - Front .
Is the repair complete?
--
YEs: Go to Step 31
--
27
Inspect for poor connections at the heated seat relay. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Yes: Go to Step 31
NO: Go to Step 28
28
Replace the heated seat relay. Refer to Relay Replacement in Wiring Systems.
Is the repair complete?
--
Yes: Go to Step 31
--
29
Inspect for poor connections at the body control module. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Yes: Go to Step 31
No: Go to Step 30
30
Replace the BCM. Refer to Body Control Module Replacement and Body Control Module (BCM) Programming/RPO Configuration in Body Control System.
Is the repair complete?
--
Yes: Go to Step 31
--
31
Operate the system in order to verify the repair.
Did you correct the condition?
--
Yes: System OK
No: Go to Step 3