DTC 19 LH Air Mix Door Motor Voltage High 2nd Design
Circuit Description
The LH temperature valve actuator is a DC stepper motor by design. The stepper motor has four field windings that are controlled by the heater and A/C control. When the heater and A/C control needs to move the stepper motor, it energizes the proper field windings which rotates the armature a fixed amount in the proper direction. This fixed amount is called a step. Battery voltage for the stepper motor is supplied by the heater and A/C control when the ignition is in the ON position.
Attached to the stepper motor is a small gear. When the stepper motor is installed on the HVAC module, it meshes with a larger gear which is part of an assembly that drives the linkage of the air mix door.
Conditions for Setting the DTC
The heater and A/C control, measures the current of all four coil wires of the stepper motor within 10 seconds when the ignition is in the ON position. The measured current is averaged by the controller and a "fail threshold" is calculated. After the output current is measured it is compared with the threshold value. If a short circuit to battery is detected on any of the low side drivers, the controller automatically protects the low side drivers by disabling all low side outputs. This step is repeated 3 times within the 10 second time frame.
Action Taken When the DTC Sets
| • | Stores a DTC 19 in the heater and A/C control memory. |
| • | The fault detection process is repeated 3 times at a fixed interval of 70 ms to allow for debouncing. |
| When the fault is set, the stepper motor can no longer be controlled. |
Conditions for Clearing the DTC
| • | The conditions for the fault are no longer present. |
| • | Using a scan tool. |
| • | A history DTC will clear after 20 consecutive ignition cycles if the conditions for the fault is no longer present. |
Diagnostic Aids
| • | If the DTC is a history or an intermittent. Try performing the tests shown while moving the harness wiring and connectors, this can often cause the malfunction to appear. |
| • | Visually inspect stepper motor connector and harness for damage, corrosion or water intrusion. |
| • | Check for adequate terminal tension, mis-routed harness, rubbed through wire insulation, and broken wire inside the insulation. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Checks the operation of the actuators to see if they are capable of moving when commanded by the heater and A/C control.
-
This step tests for a short to battery with and without the ignition in the ON position.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Air Delivery System Check Performed? | -- | ||
NOTE: Until the stepper motor reaches the commanded position the status of this parameter changes from INACTIVE to ACTIVE. Does the scan tool display ACTIVE for the motor and 100% for the position? | -- | |||
3 | Repeat the above steps but turn the temperature knob to maximum cooling. Does the scan tool display ACTIVE for the motor and 0% for the position? | -- | ||
Are the voltage readings within the specified value? | Less than 0.1 V | |||
5 |
Is a current DTC 19 present? | -- | ||
6 | Locate and repair the short to B+ in the circuit(s) that failed the test Is the repair complete? | -- | -- | |
7 | Replace and program the heater and A/C control. Refer to Control Assembly Replacement Is the replacement and programming complete? | -- | -- |
