• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Ignition | 1 | 1 | -- | -- |
Ground | -- | 1 | -- | -- |
1. Vacuum Pump Inoperative |
The HVAC control assembly uses vacuum to control the mode doors. Vehicles equipped with diesel engines use a vacuum pump to create vacuum. The vacuum pump has ignition voltage circuit and a ground circuit to operate. The pump turns on when vacuum is low and turns off when vacuum reaches 21 Hg.
Control Module References for scan tool information
⇒ | If the blower motor speed does not change or fails to operate at a selected speed, refer to Blower Motor Malfunction . |
⇒ | If the air flow fails to blow through the selected outlets, refer to Vacuum Control System Diagnostic . |
⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.