GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The heated seat temperature sensor that set this DTC is located in the seat cushion just under the seat cover with the seat heating element. The body control module (BCM) supplies a 10-volt signal and a low reference circuit to the sensor. The BCM monitors the voltage of the heated seat temperature sensor signal circuit to determine the temperature of the seat. The BCM will then cycle the heated seat relay ON and OFF in order to maintain the desired seat temperature based on the voltage feedback from the temperature sensor.

The BCM also monitors the sensor signal circuit for a change in voltage that is either too fast or too slow. The slow rate check is performed only when the heated seat is initially turned ON with a cold seat in order to prevent setting a false DTC.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC B1920 Seat Heater Timer Circuit
    • DTC B2165 Seat Heater Timer Circuit

Conditions for Running the DTC

    • The BCM must be powered and cannot have B1327, Battery Voltage Low, as an active DTC for this DTC to set.
    • The module voltage must be 9-16 volts.
    • The heated seat system is active.

Conditions for Setting the DTC

    • The BCM detects that the change in voltage of the temperature sensor signal circuit is either too fast or too slow.
    • The BCM performs the slow rate check only when the heated seat is initially turned on in order to prevent setting a false DTC.
    • The slow rate check may take the BCM 10 minutes to set a DTC.

Action Taken When the DTC Sets

    • The BCM will turn OFF the heated seat operation.
    • Current and history codes are stored.

Conditions for Clearing the DTC

The current DTC will clear whenever the diagnostic feedback to the BCM indicates that the fault no longer exists.

Diagnostic Aids

    • Because the BCM takes approximately 10 minutes to set this DTC, the tests in this diagnostic table are performed without the DTC being active.
    • Faults in circuits of the heated seat system other than the temperature sensor may cause this DTC to set.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. If an active DTC is set, the BCM will turn OFF the heated seat relay, not allowing for an accurate test of the relay. By cycling the ignition switch, the BCM turns OFF the active DTC allowing for an accurate test.

  2. This test determines the functionality of the heated seat relay.

  3. This test verifies the repair.

Step

Action

Value(s)

Yes

No

Schematic Reference: Heated/Cooled Seat Schematics

Connector End View Reference: Power Seat Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn OFF the ignition.
  2. Turn ON the ignition, with the engine OFF.
  3. Connect a test lamp from the heated seat element supply voltage circuit of the heated seat relay to a good ground.
  4. Turn ON the heated seat to the high heat position.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 3

3

  1. Disconnect the heated seat relay.
  2. Connect a test lamp from the battery positive voltage circuit of the relay connector to ground.

Does the test lamp illuminate?

--

Go to Step 13

Go to Step 18

4

  1. Disconnect the heated seat relay.
  2. Measure the resistance from the heated seat element supply voltage circuit of the relay connector to ground.

Does the resistance measure less than the specified value?

5 ohms

Go to Step 7

Go to Step 5

5

  1. Disconnect the seat cushion heater element.
  2. Measure the resistance across the circuits of the seat cushion heater element harness connector.

Does the resistance measure less than the specified value?

5 ohms

Go to Step 6

Go to Step 14

6

  1. Disconnect the seat back heater element.
  2. Measure the resistance across the circuits of the seat back heater element harness connector.

Does the resistance measure less than the specified value?

5 ohms

Go to Step 10

Go to Step 15

7

Important: If the resistance is measured with the seat still warm, the resistance may vary outside of the specified range since the thermistor resistance varies with temperature.

  1. Disconnect the body control module (BCM) connector C2.
  2. Measure the resistance between the temperature sensor signal circuit and the sensor low reference circuit of the BCM connector.

Does the resistance measure within the specified range?

535-168,000 ohms

Go to Step 12

Go to Step 8

8

Test the heated seat temperature sensor signal circuit and the temperature sensor low reference circuit, between the BCM and the temperature sensor, for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 9

9

Test the heated seat temperature sensor signal circuit, between the BCM, and the temperature sensor for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 14

10

Test the heated seat element supply voltage circuit between the heated seat relay and the seat cushion heating element for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 11

11

Test the heated seat element supply voltage circuit between the seat cushion heating element and the seat back heating element for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 17

12

Test the heated seat element supply voltage circuit between the seat cushion heating element and the seat back heating element for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 16

13

Inspect for poor connections at the harness connector of the heated seat relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 19

14

Inspect for poor connections at the harness connector of the heated seat cushion heating element/temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 20

15

Inspect for poor connections at the harness connector of the heated seat back heating element. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 20

16

Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 22

Go to Step 21

17

Repair the open in the ground circuit of the seat heating elements. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 22

--

18

Repair the short to ground or open in the battery positive voltage circuit of the heated seat relay. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 22

--

19

Replace the heated seat relay. Refer to Front Seat Heater Relay Replacement .

Did you complete the replacement?

--

Go to Step 22

--

20

Replace the heated seat cushion heating element/temperature sensor or seat back heating element. Refer to Driver or Passenger Seat Back Cushion Heater Replacement and Driver or Passenger Seat Cushion Heater Replacement .

Did you complete the replacement?

--

Go to Step 22

--

21

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 22

--

22

  1. Clear the DTCs using the scan tool.
  2. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK