B0408

Diagnostic Trouble Code Chart (Part 1 Of 3):

Diagnostic Trouble Code Chart (Part 2 Of 3):

Diagnostic Trouble Code Chart (Part 3 Of 3):

Wiring Schematics:

CIRCUIT DESCRIPTION
The air temperature valve sensor and motor is driven by the Electronic Climate Control (ECC) 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 ECC module will know the position of the temperature valve.
A low voltage at CKT 733 (about 1.0 volt) represents a cold air mix door position.
A high voltage on CKT 733 (about 4.0 volts) represents a hot air mix door position.
The ECC module drives the air temperature valve sensor and motor through CKT 1199 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 on CKT 1199 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 on CKT 1199 will cause the air temperature valve sensor and motor to stop.

CONDITIONS FOR SETTING THE DTC
The ECC module will detect DTC B0408 when the ignition switch is in the ON position and one of the following conditions exists:
- CKT 341 is open
- CKT 733 is shorted to voltage, ground, or open.
- CKT 1199 is shorted to voltage, ground, or open.
- CKT 1688 is shorted to voltage, ground, or open.
- CKT1791 is open.
- The ECC 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 valve.

ACTION TAKEN WHEN THE DTC SETS
The ECC module will drive the temperature valve to the FULL COLD position if the system is in one of the following modes:
- PANEL
- BI-LEVEL
- AUTO PANEL/AUTO BI-LEVEL

The ECC module will drive the temperature valve to the full heat position it 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 may only be cleared by removing and restoring B+ or by using the scan tool.

DIAGNOSTIC AIDS
- The ECC module may set class 2 lost communication DTCs when the Body Control Module (BCM) or the Vehicle Control Module (VCM) is being reprogrammed. After reprogramming, inspect for DTCs in the ECC 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 ECC module and then restored for any reason, the ECC 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.
2. This step inspects the current DTC.
3. This step inspects for battery voltage at the air temperature valve sensor and motor.
4. This step inspects for a short to battery on CKT 1199/1688/733.
5. This step determines if the air temperature valve sensor and motor is shorted to battery voltage.
6. This step isolates the short to battery to the ECC module or CKT 1199/16881733.
7. This step repairs the short to battery in CKT 1199/1688/733.
8. This step inspects for an open in CKT 1199/1688/733.
9. This step substitutes a known good air temperature valve sensor and motor.
10. This step inspects the mechanical linkage.
11. This step repairs an open in CKT 1199/1688/733.
12. This step replaces the ECC module.
13. This step repairs a mechanical malfunction.
14. This step inspects for a short to ground in CKT 1199/1688/733.
15. This step repairs a short to ground in CKT 1199/1688/733.
16. This step replaces a defective air temperature valve sensor and motor.
17. This step repairs an open in CKT 341.
18. This step tests the continuity of CKT 1791.
19. This step repairs an open in CKT 1791.
20. This step determines if the air temperature valve gasket material is causing history DTC B0408 to falsely set.
21. This step inspects the temperature control values.
22. This step clears any DTCs.
23. This step inspects the air temperature valve for binding.
24. This step determines if DTC B0408 has cleared.