Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Ignition 3 Voltage Circuit of the Air Temperature Actuator | -- | B408 05 B408 06 B418 05 B418 06 | -- | -- |
Ground Circuit of the Air Temperature Actuator | -- | B408 05 B408 06 B418 05 B418 06 | -- | -- |
5-Volt Reference Circuit of the Air Temperature Actuator | -- | B408 05 B408 06 B418 05 B418 06 | -- | -- |
Air Temperature Actuator Position Signal | -- | B408 05 B408 06 B418 05 B418 06 | -- | -- |
Air Temperature Actuator Control Circuit | -- | B408 05 B408 06 B418 05 B418 06 | -- | -- |
Circuit Description
The HVAC control module commands the air temperature actuator movement with one of 3 voltage signals applied to the air temperature door control circuit. A low voltage of 0 volts moves the air temperature door toward full cold. A voltage of 2.5 volts stops the actuator. A high voltage of 5 volts moves the air temperature door toward full hot. The HVAC control module determines the current position of the actuator by monitoring the feedback voltage of the air temperature door position signal circuit. The feedback potentiometer position is a function of the actuator position. A high voltage indicates a full hot air temperature door position. A low voltage indicates a full cold air temperature door position. The HVAC control module controls the air temperature door position in order to maintain the selected air temperature.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC B0408 Temperature Control 1 Main Circuit |
| • | DTC B0418 Temperature Control 2 Passenger Circuit |
Conditions for Running the DTC
| • | The ignition is turned ON. |
| • | Ignition voltage is between 9-16 volts. |
Conditions for Setting the DTC
| • | The air temperature position signal is less than 5 counts. |
| • | The air temperature position signal is greater than 194 counts. |
| • | The air temperature actuator actual total travel range max-min is less than or greater than the range limits. |
Action Taken When the DTC Sets
| • | The HVAC control module will continue to make use of whatever air temperature actuator travel range is still available. |
| • | The DTC is stored in DTC information. |
Conditions for Clearing the DTC
| • | The DTC will become history if the HVAC control module no longer detects a failure. |
| • | The history DTC will clear after 50 fault-free ignition cycles. |
| • | The DTC can be cleared with a scan tool. |
Diagnostic Aids
| • | A damaged or broken air temperature actuator or mode door can cause this DTC to set. |
| • | If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections . |
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | ||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||
2 |
Does the air temperature actuator drive shaft rotate for each selected position? | -- | Go to Step 3 | Go to Step 4 | ||||||
3 | Inspect the air temperature actuator for the following conditions:
Did you find and correct the condition? | -- | Go to Step 15 | Go to Diagnostic Aids | ||||||
4 | Test the ignition 3 voltage circuit of the air temperature actuator for an open or a high resistance. Refer to Circuit Testing or Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 5 | ||||||
5 | Test the ground circuit of the air temperature actuator for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 6 | ||||||
6 | Test the 5-volt reference circuit of the air temperature actuator for an open, a high resistance, short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 7 | ||||||
7 | Test the air temperature position signal circuit of the air temperature actuator for an open, a high resistance, a short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 8 | ||||||
8 | Test the air temperature control circuit of the air temperature actuator for an open, a high resistance, a short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 9 | ||||||
9 |
Important: The air temperature actuator connector and the HVAC controller connector must be connected to correctly perform the test.
Does the air temperature actuator drive shaft rotate and does the voltage change? | -- | Go to Step 10 | Go to Step 11 | ||||||
10 |
Does the voltage measure near the specified value when airflow moves toward Full Cold decreasing, near the specified value when airflow moves toward Full Hot increasing, and near the specified value when stationary? | 0 V decreasing 5 V increasing 2.5 V stationary | Go to Step 11 | Go to Step 12 | ||||||
11 | Inspect for poor connections at the harness connector of the air temperature actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13 | ||||||
12 | 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 . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 | ||||||
13 | Replace the air temperature actuator. Refer to Temperature Valve Actuator Replacement - Left Side or Temperature Valve Actuator Replacement - Right Side . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||
14 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||
15 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2 | ||||||
