GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Blazer - 4WD - RHD 🢒 DTC 🢒 DTC B0408 Temperature Control #1 (Main/Front) Circuit Malfunction

Object Number: 425171 Size: MF

Circuit Description

The air temperature valve sensor and motor is driven by the electronic climate control module. The air temperature valve sensor and motor operates the temperature valve. The position of the temperature valve is adjusted in order to maintain the verified air-outlet temperature. A feedback potentiometer is used in the flat-pack motor so that the electronic climate control module will know the position of the temperature valve.

A low voltage at CKT 733 (LT BLU) (about 1.0 volt) represents a cold air mix door position.

A high voltage at CKT 733 (LT BLU) (about 4.0 volts) represents a hot air mix door position.

The electronic climate control module drives the air temperature valve sensor and motor through CKT 1199 (DK BLU) to the logic portion of the air temperature valve sensor and motor. The air temperature valve sensor and motor will cause the temperature valve to move to the full heat position. Applying 0.0 volts to CKT 1199 (DK BLU) to the logic portion of the air temperature valve sensor and motor will cause the temperature valve to move to the full cold position. Applying approximately 2.5 volts to CKT 1199 (DK BLU) will cause the air temperature valve sensor and motor to stop.

Conditions for Setting the DTC

The electronic climate control module will detect DTC B0408 when the ignition switch is in the ON position and one of the following conditions exists:

    • CKT 1199 is shorted to voltage.
    • CKT 1199 is shorted to ground.
    • CKT 1199 is open.
    • The electronic climate control module does not sense the expected change in temperature door position when the air temperature valve sensor and motor has been commanded to move the temperature door.

Action Taken When the DTC Sets

The electronic climate control module will drive the temperature door to the full cold position if the system is in one of the following modes:

    • PANEL
    • BI-LEVEL
    • AUTO PANEL/AUTO BI-LEVEL

The electronic climate control module will drive the temperature door to the full heat position if the system is in one of the following modes:

    • LOWER
    • DEFOG
    • DEFROST
    • AUTO LOWER

Conditions for Clearing the MIL/DTC

DTC B0408 will clear as soon as the fault goes away or has been repaired. The system will then return to normal operation. History DTCs can only be cleared by removing and restoring B+ or by using the scan tool.

Diagnostic Aids
    • The electronic climate control module may set class 2 lost communication DTCs when the body control module (BCM) or the vehice control module (VCM) is being reprogrammed. After reprogramming, inspect for DTCs in the electronic climate control module. Clear any history U DTCs then resume diagnostics.
    • Visually inspect the air temperature valve sensor and motor and harness connector for loose or bent pins. If B+ has been removed from the electronic climate control module and then restored for any reason, the electronic climate control module system will (one time) drive the temperature door to full hot and then to full cold positions when power is restored.

Test Description

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

  1. This step inspects the current DTC.

    2.

  2. This step inspects for battery voltage at the air temperature valve sensor and motor.

    3.

  3. This step inspects for a short to battery on CKT 1199/1688/733.

    4.

  4. This step determines if the air temperature valve sensor and motor is shorted to battery voltage.

    5.

  5. This step isolates the short to battery to the electronic climate control module or CKT 1199/1688/733.

    6.

  6. This step repairs the short to battery in CKT 1199/1688/733.

    7.

  7. This step inspects for an open in CKT 1199/1688/733.

    8.

  8. This step substitutes a known good air temperature valve sensor and motor.

    9.

  9. This step inspects the mechanical linkage.

    10.

  10. This step repairs an open in CKT 1199/1688/733.

    11.

  11. This step replaces the electronic climate control module.

    12.

  12. This step repairs a mechanical malfunction.

    13.

  13. This step inspects for a short to ground in CKT 1199/1688/733.

    14.

  14. This step repairs a short to ground in CKT 1199/1688/733.

    15.

  15. This step replaces a defective air temperature valve sensor and motor.

    16.

  16. This step repairs an open in CKT 341.

    17.

  17. This step tests the continuity of CKT 1791.

    18.

  18. This step repairs an open in CKT 1791.

  1. This step determines if the air temperature valve gasket material is causing history DTC B0408 to falsely set.

    2.

  2. This step inspects the temperature control values.

    3.

  3. This step clears any DTCs.

    4.

  4. This step inspects the air temperature valve for binding.

    5.

  5. This step determines if DTC B0408 has cleared.

Step

Action

Value(s)

Yes

No

Tools Required

    • Scan Tool
    • J 39200 Digital Multimeter (DMM)
    • J 35616-A Connector Test Adapter Kit

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check

2

Is DTC B0408 set as a current DTC?

--

Go to Step 3

Go to Step 20

3

  1. Turn the ignition switch to the ON position.
  2. Backprobe the connector for battery voltage on the air temperature valve sensor and motor connector terminal 1 to battery ground.

Is the voltage within the specified range?

9-16 V

Go to Step 4

Go to Step 17

4

  1. Turn the ignition switch to the ON position.
  2. Backprobe the connector for battery voltage on the electronic climate control module connector terminal C9 to battery ground, and terminal D5 to battery ground.

Is the voltage within the specified range?

9-16 V

Go to Step 5

Go to Step 8

5

  1. Disconnect the air temperature valve sensor and motor. Refer to Interior Trim.
  2. Test for battery voltage on the electronic climate control module connector at the following terminals:
    3. • C9 to battery ground
    • C4 to battery ground
    • D5 to battery ground

Is the voltage within the specified range?

9-16 V

Go to Step 6

Go to Step 16

6

  1. Disconnect the electronic climate control module.
  2. Test for battery voltage on the electronic climate control module connector at the following terminals:
    3. • C9 to battery ground
    • C4 to battery ground
    • D5 to battery ground

Is the voltage within the specified range?

9-16 V

Go to Step 7

Go to Step 12

7

Repair the short to battery in the following circuits:

    • CKT 1199 (DK BLU)
    • CKT 1688 (LT BLU/BLK)
    • CKT 733 (LT BLU)

Is the repair complete?

--

Go to Diagnostic System Check

--

8

  1. Disconnect the air temperature valve sensor and motor.
  2. Disconnect the electronic climate control module.
  3. Measure the resistance between electronic climate control module connector terminal C9 and air temperature valve sensor and motor connector terminal 2.
  4. Repeat the above procedure on electronic climate control module connector terminal C4 to air temperature valve sensor and motor connector terminal 5 and electronic climate control module connector terminal D5 to air temperature valve sensor and motor connector terminal 6.

Is the resistance less than the specified value?

5 ohms

Go to Step 14

Go to Step 11

9

  1. Connect a known working air temperature valve sensor and motor to the harness connector.
  2. Cycle the test air temperature valve sensor and motor from the electronic climate control module. Cycle from 18°C (65°F) to 30°C (85°F) back to 18°C (65°F).
  3. Inspect for air temperature valve sensor and motor operation.

Does the test air temperature valve sensor and motor operate correctly?

--

Go to Step 10

Go to Step 12

10

  1. Remove the air temperature valve sensor and motor.
  2. Inspect for the operation of the air temperature valve sensor and motor mechanism.

Does binding exist?

--

Go to Step 13

Go to Step 24

11

Repair the open in the following circuits:

    • CKT 1199 (DK BLU)
    • CKT 1688 (LT BLU/BLK)
    • CKT 733 (LT BLU)

Is the repair complete?

--

Go to Diagnostic System Check

--

12

Replace the electronic climate control module.

Is the replacement complete?

--

Go to Diagnostic System Check

--

13

Repair or replace the air temperature valve assembly.

Is the repair complete?

--

Go to Diagnostic System Check

--

14

  1. Measure the resistance between electronic climate control module connector terminal C9 and battery ground.
  2. Repeat the above procedure on electronic climate control module connector terminal C4 to battery ground and electronic climate control module connector terminal D5 to battery ground.

Is the resistance less than the specified value?

5 ohms

Go to Step 15

Go to Step 18

15

Repair the short to ground in the following circuits:

    • CKT 1199 (DK BLU)
    • CKT 1688 (LT BLU/BLK)
    • CKT 733 (LT BLU)

Is the repair complete?

--

Go to Diagnostic System Check

--

16

Replace the air temperature valve sensor and motor.

Is the replacement complete?

--

Go to Diagnostic System Check

--

17

Repair the open in CKT 341 between splice S213 and the air temperature valve sensor and motor connector terminal 1.

Is the repair complete?

--

Go to Diagnostic System Check

--

18

Measure the resistance between air temperature valve sensor and motor connector terminal 3 and battery ground.

Is the resistance less than the specified value?

5 ohms

Go to Step 9

Go to Step 19

19

Repair the open in CKT 1791 (YEL).

Is the repair complete?

--

Go to Diagnostic System Check

--

20

  1. Turn the ignition switch to the ON position.
  2. Connect the scan tool.
  3. Record the air temperature valve sensor and motor MAX and MIN position values.
  4. Rotate the temperature control knob to full hot. Note the air mix actual mix.
  5. Rotate the temperature control knob to full cold. Note the air mix actual value.
  6. Compare the full hot (MAX) and full cold (MIN) actual values to the recorded values.

Is the difference greater than the specified value?

10

Go to Step 23

Go to Step 21

21

Disregard the history DTC B0408.

Has the step been completed?

--

Go to Diagnostic System Check

--

22

Clear any electronic climate control module DTCs.

Does the DTC clear?

--

Go to Diagnostic System Check

Go to Intermittents and Poor Connections Diagnosis in Wiring Systems

23

  1. Remove the air temperature valve sensor and motor assembly.
  2. Inspect the operation of the air temperature valve mechanism.

Is the door binding?

--

Go to Step 13

Go to Step 22

24

Clear the electronic climate control module DTCs.

Does DTC B0408 clear?

--

Go to Diagnostic System Check

Go to Step 12