GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Tahoe - 2WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 Too Cold in Vehicle - Auxiliary

Test Description

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

  1. This step ensures that the primary HVAC system is functioning properly.

    2.

  2. The DTCs listed could set if a calibration of the actuators is performed.

    3.

  3. If the condition does not occur when a heating request has been made then you must bypass the A/C compressor and cooling system diagnostic information.

    4.

  4. This step ensures that the front auxiliary control assembly is providing an auxiliary air temperature input to the auxiliary HVAC control module.

    5.

  5. This step ensures that the rear seat audio control is providing an auxiliary air temperature input to the auxiliary HVAC control module.

    6.

  6. When taking temperature reading allow for a 3°C (5°F) temperature variance.

    7.

  7. When the front auxiliary HVAC control assembly is disconnected, and there is no fault on auxiliary air temperature switch control circuit, the scan tool will read a high count value for the Air Temp. Switch Pos. parameter. A short to ground on circuit will have low count value.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: Auxiliary air temperature can not be adjusted from one or both auxiliary controls or auxiliary heating is insufficient.

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Important:: The auxiliary HVAC control assembly operates independently of the HVAC control module to provide heated airflow through the auxiliary system.

Does the HVAC control module operate and provide sufficient heating?

--

Go to Step 3

Go to Too Cold in Vehicle

3

Important:: If during this diagnostic procedure the auxiliary HVAC control module is disconnected a recalibration of actuators must be performed to avoid misdiagnosis.

  1. Recalibrate actuators. Refer to Actuator Recalibration .
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the current DTC list in Rear Aux. Climate Module using the scan tool.

Does the scan tool display DTC B0434 or B3764?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 4

4
  1. Turn ON the ignition, with the engine OFF.
  2. Select AUX on the front auxiliary HVAC control assembly.
  3. Place the auxiliary blower motor switch on the rear seat audio control module in each speed position.

Does the auxiliary blower motor operate at all?

--

Go to Step 5

Go to Auxiliary Blower Motor Inoperative

5

Does the auxiliary blower motor operate at the desired speed for each speed position?

--

Go to Step 6

Go to Auxiliary Blower Motor Malfunction

6

Does the Auxiliary Too Cold in Vehicle concern occur when heating is required?

--

Go to Step 7

Go to Step 9

7
  1. Start the engine.
  2. Place the blower motor switch in the OFF position on the HVAC control module.
  3. Place the mode switch on the HVAC control module to the Floor position.
  4. Place the A/C request switch in the OFF position on the HVAC control module.

Does the A/C compressor operate?

--

Go to HVAC Compressor Clutch Does Not Disengage

Go to Step 8

8

Inspect the cooling system for the following:

    • A low coolant level
    • A loose or worn accessory drive belt
    • A leaking radiator hose or auxiliary heater hoses
    • A kinked radiator hose or auxiliary heater hoses
    • A missing radiator cap pressure seal
    • A leaking radiator cap

Did you find and correct the condition?

--

Go to Step 32

Go to Step 9

9

  1. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, observe the Air Temp. Switch Pos. data parameter in the Rear Aux. Climate Module/Front Aux. Controls data list.
  3. Place the front auxiliary blower motor switch to the maximum speed.
  4. Place the front auxiliary air temperature switch on the front auxiliary HVAC control assembly from the coldest to hottest position.

Does the Air Temp. Switch Pos. parameter change from a low count to high count?

--

Go to Step 10

Go to Step 13

10

  1. Select AUX on the front auxiliary HVAC control assembly.
  2. Press the power button for the auxiliary HVAC controls on the rear seat audio control module.
  3. Place the auxiliary air temperature switch on the rear seat audio control module from the coldest to hottest position.
  4. Observe the Rear Temp. Select Sw. parameter in the Rear HVAC data list.

Does the Rear Temp. Select Sw. parameter change with each air temperature button press?

--

Go to Step 11

Go to Step 24

11
  1. With a scan tool, command the Inside Air Temp Sensor Fan ON in the Rear Aux. Climate Module Special Functions.
  2. Inspect for air flow through the auxiliary inside air temperature sensor by placing a 5  cm (2 in) square piece of paper over the sensor air inlet.

Does the paper stay in place?

--

Go to Step 12

Go to Step 16

12

  1. Turn ON the ignition, with the engine OFF.
  2. Place a thermometer near the auxiliary inside air temperature sensor, auxiliary upper and lower air temperature sensors.
  3. Measure the resistance of the auxiliary inside air temperature sensor, the upper and lower auxiliary air temperature sensors. Refer to Sensor Resistance Table .
  4. Compare the resistance of the sensor to the temperature value of the thermometer.

Does the resistance measure near the sensor resistance table value?

--

Go to Step 23

Go to Step 25

13
  1. Disconnect the front auxiliary HVAC control assembly.
  2. Measure the voltage of the 5-volt reference circuit of the front auxiliary HVAC control assembly to a good ground.

Does the voltage measure near specified value?

5 V

Go to Step 14

Go to Step 18

14

Measure the voltage of the 5-volt reference circuit to the low reference circuit of the front auxiliary HVAC control assembly.

Does the voltage measure near specified value?

5 V

Go to Step 15

Go to Step 20

15

  1. Connect a 3-ampere fused jumper wire between the low reference circuit and the auxiliary front air temperature switch signal circuit of the front auxiliary HVAC control assembly.
  2. With a scan tool, observe the Air Temp. Switch Pos. data parameter in the Rear Aux. Climate Module/Front Aux. Controls data list.

Do the counts read below specified value?

5 Counts

Go to Step 26

Go to Step 19

16
  1. Disconnect the auxiliary inside air temperature sensor.
  2. With a scan tool, command the Inside Air Temp Sensor Fan ON in the Rear Aux. Climate Module Special Functions.
  3. Measure the voltage of the auxiliary inside air temperature sensor assembly control circuit of the auxiliary inside air temperature sensor assembly to a good ground.

Does the voltage measure near specified value?

12 V

Go to Step 17

Go to Step 21

17
  1. With a scan tool, command the Inside Air Temp Sensor Fan ON in the Rear Aux. Climate Module Special Functions.
  2. Measure the voltage of the auxiliary inside air temperature sensor assembly control circuit to the ground circuit of the auxiliary inside air temperature sensor assembly.

Does the voltage measure near specified value?

12 V

Go to Step 25

Go to Step 22

18

Test the 5-volt reference circuit of the front auxiliary HVAC control assembly for the following conditions:

    • A short to voltage
    • A short to ground
    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 27

19

Test the auxiliary front air temperature switch signal circuit of the front auxiliary HVAC control assembly for the following conditions:

    • A short to voltage
    • A short to ground
    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 27

20

Test the low reference circuit of the front auxiliary HVAC control assembly for the following conditions:

    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 27

21

Test the auxiliary inside air temperature sensor assembly control circuit of the auxiliary inside air temperature sensor assembly for the following conditions:

    • A short to ground
    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 27

22

Repair the ground circuit of the auxiliary inside air temperature sensor assembly. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

--

23

Check the suspect air temperature sensor for proper installation. Refer to Air Temperature Sensor Replacement - Upper Auxiliary or Air Temperature Sensor Replacement - Lower Auxiliary .

Did you find and correct the condition?

--

Go to Step 32

Go to Heating Performance Diagnostic in Heating, Ventilation and Air Conditioning

24

Inspect for poor connections at the harness connector of the rear seat audio control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 28

25

Inspect for poor connections at the harness connector of the suspect air temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 29

26

Inspect for poor connections at the harness connector of the front auxiliary HVAC control assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 30

27

Inspect for poor connections at the harness connector of the auxiliary HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 31

28

Replace the rear seat audio control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 32

--

29

Replace the suspect air temperature sensor. Refer to one of the following procedures:

Did you complete the replacement?

--

Go to Step 32

--

30

Replace the front auxiliary HVAC control assembly. Refer to Auxiliary Heater and Air Conditioning Control Replacement - Front .

Did you complete the replacement?

--

Go to Step 32

--

31

Replace the auxiliary HVAC control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 32

--

32

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2