GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 GMC K Sierra - 4WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 Too Cold in Vehicle

Diagnostic Aids
    • The condition may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • The air temperature actuators can be calibrated. Refer to Actuator Recalibration .

Test Description

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

  1. This step ensures that the lower air temperature sensors operate properly. The LH and RH Heater Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensors circuits or the sensor itself then the count value of the effected sensor would remain high.

    2.

  2. This step ensures that the upper air temperature sensors operate properly. The LH and RH AC Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensors circuits or the sensor itself then the count value of the effected sensor would remain high.

    3.

  3. This action ensures that the internal fan of the inside air temperature sensor assembly is providing air flow across the internal sensor.

    4.

  4. Use the following table to determine that the recorded scan tool values are within range for the recorded probe temperatures.

Temperature °C

Temperature °F

Scan Tool Display

0-4

32-40

206-175 counts

5-9

41-49

194-161 counts

10-14

50-58

180-145 counts

15-19

59-67

166-133 counts

20-24

68-76

150-119 counts

25-29

77-85

136-106 counts

30-34

86-94

121-93 counts

35-39

95-103

107-81 counts

40-44

104-112

94-69 counts

45-49

113-121

83-59 counts

50-54

122-130

72-51 counts

55-59

131-139

63-44 counts

60-64

140-148

55-37 counts

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: The temperature can not be adjusted, or heating is insufficient.

1

Did you perform the HVAC Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2

Important: If during this diagnostic procedure the 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 Diagnostic Trouble Code (DTC) List .

Does the scan tool display any DTC B0229, B0414, B0424 or B3770?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Turn ON the HVAC control module.
  3. Place the mode switch in the PANEL position.
  4. Place the blower motor switch in each speed position.

Does the blower motor operate in any of the speed positions speed?

--

Go to Step 4

Go to Blower Motor Inoperative

4

Does the blower motor operate in all desired speed positions?

--

Go to Step 5

Go to Blower Motor Malfunction

5
  1. Place the recirculation switch in the ON position.
  2. Observe the recirculation door.
  3. Place the recirculation switch in the OFF position.

Does the recirculation door move from the recirculation position to the outside air position?

--

Go to Step 6

Go to Air Recirculation Malfunction

6
  1. Start the engine.
  2. Place the mode switch in PANEL position.
  3. Place the A/C request switch in the ON position.
  4. Observe the A/C compressor clutch.
  5. Place the A/C request switch in the OFF position.

Does the A/C compressor clutch disengage?

--

Go to Step 7

Go to HVAC Compressor Clutch Does Not Disengage

7

Perform the Heating Performance Diagnostic. Refer to Heating Performance Diagnostic .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 8

8

  1. Start the engine.
  2. Wait until engine coolant temperature reaches its normal operating temperature.
  3. Place the mode switch to the Floor position.
  4. Place the drivers air temperature switch to the warmest position.
  5. With a scan tool, observe the right and left Heater Duct Actual and Heater Duct Desired parameters.
  6. Wait 3 minutes to allow the duct air temperature to stabilize.

Do both of the Heater Duct Actual parameter values increase within 15 Counts of the Heater Duct Desired parameter?

--

Go to Step 9

Go to Step 20

9

  1. Place the mode switch to the Panel position.
  2. Place the drivers air temperature switch to the warmest position.
  3. With a scan tool, observe the right and left AC Duct Actual and AC Duct Desired parameters.
  4. Wait 3 minutes to allow the duct air temperature to stabilize.

Do both of the AC Duct Actual parameter values increase within 15 Counts of the AC Duct Desired parameter?

--

Go to Step 10

Go to Step 20

10

Check the air temperature sensors for proper installation.

Refer to the following procedures:

Did you find and correct the condition?

--

Go to Step 28

Go to Step 11

11

  1. Turn ON the ignition, with the engine OFF.
  2. Inspect for air flow through the inside air temperature sensor assembly by placing a 5 cm (2 in) square piece of paper over inlet of the inside air temperature sensor assembly.

Does the paper stay in place?

--

Go to Step 13

Go to Step 12

12
  1. Turn the ignition OFF.
  2. Disconnect the inside air temperature sensor assembly.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the inside air temperature sensor assembly control circuit of the inside air temperature sensor assembly with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 18

Go to Step 17

13
  1. Turn ON the ignition with the engine OFF.
  2. Install a scan tool.
  3. Cover the sunload sensor.
  4. With a scan tool, observe the Left Solar Sensor and Right Solar Sensor parameters in the Body Control Module data list.

Does the scan tool indicate that the Left Solar Sensor and Right Solar Sensor parameters are greater than the specified value?

220 Counts

Go to Step 14

Go to Step 23

14
  1. Place the temperature probe of the J 43600 near the inside air temperature sensor assembly.
  2. With a scan tool, observe the Inside Air Temp parameter in the Heating and Air Conditioning Data list.

Does the scan tool indicate that the Inside Air Temp parameter is within 3°C (5°F) of the probe temperature?

--

Go to Step 15

Go to Step 19

15
  1. Start the engine.
  2. Place the blower motor switch in the minimum speed position.
  3. Allow the engine to reach normal operating temperature.
  4. Place the blower motor switch in the maximum speed position.
  5. Place the left and right air temperature switches in the FULL HOT positions.
  6. Place the mode switch in the bi-level position.
  7. Wait 3 minutes to allow the discharge air temperatures to stabilize.
  8. With a scan tool, record the values of the following parameters in the Heating and Air Conditioning data list:
    9. • LH AC Duct Actual
    •  LH Heater Duct Actual
    •  RH AC Duct Actual
    • RH Heater Duct Actual
  9. With the temperature probes of the J 43600 , record the air temperatures near the following sensors:
    10. • The left upper air temperature sensor
    • The left lower air temperature sensor
    • The right upper air temperature sensor
    • The right lower air temperature sensor

Are the parameter values within the specified range for the recorded air temperatures?

--

Go to Diagnostic Aids

Go to Step 16

16
  1. Turn OFF the ignition.
  2. Disconnect the suspect air temperature sensor.
  3. Place the temperature probe of the J 43600 near the air temperature sensor.
  4. Record the probe temperature.
  5. Measure the resistance of the air temperature sensor. Refer to the Sensor Resistance Table .

Does the resistance measure near the specified range?

--

Go to Step 24

Go to Step 20

17

Test the inside air temperature sensor assembly control circuit of the inside air temperature sensor assembly for an open, a high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 24

18

Test the ground circuit of the inside air temperature sensor assembly for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition

--

Go to Step 28

Go to Step 22

19
  1. Turn OFF the ignition.
  2. Disconnect the inside air temperature assembly.
  3. Place the temperature probe of the J 43600 near the inside air temperature sensor assembly.
  4. Record the probe temperature.
  5. Measure the resistance of the inside air temperature sensor. Refer to the Sensor Resistance Table .

Does the resistance measure within the specified range ?

--

Go to Step 24

Go to Step 20

20

Test the signal circuit of the suspect air temperature sensor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 21

21

Test the low reference circuit of the suspect air temperature sensor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 22

22

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 28

Go to Step 25

23

Inspect for poor connections at the harness connector of the sunload 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 28

Go to Step 26

24

Inspect for poor connections at the harness connector of the 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 28

Go to Step 27

25

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

Did you complete the replacement?

--

Go to Step 28

--

26

Replace the sunload sensor. Refer to Sun Load Sensor Replacement .

Did you complete the replacement?

--

Go to Step 28

--

27

Replace the HVAC control module. Refer to HVAC Control Module Replacement .

Did you complete the replacement?

--

Go to Step 28

--

28

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2