• | 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 provide an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
HVAC Relay B+ | 2 | 2 | -- | -- |
HVAC Control Module B+ | 2 | 2 | -- | -- |
Blower Motor Resistor Control | 1 | 1 | 1 | -- |
Relay Controlled Output Circuit | 2 | 2 | -- | -- |
Run Relay Control | 2 | 2 | 2 | -- |
Blower Motor Control | 2 | 2 | -- | -- |
HVAC Relay Ground | -- | 2 | 2 | -- |
HVAC Control Module Ground | -- | 2 | 2 | -- |
1. Blower Motor Malfunction 2. Blower Motor Inoperative |
The HVAC control assembly applies a ground to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:
• | Low speed, 3 resistors |
• | Medium 1 speed, 2 resistors |
• | Medium 2 speed, 1 resistor |
When the operator requests high speed, the HVAC control module applies ground directly to the blower motor.
When the OFF position is selected, the HVAC control module applies ground to the off input within the HVAC control module through the off blower motor control circuit. When the HVAC control module receives this input, any air conditioning (A/C) requests will be cancelled and the A/C request LED will not be illuminated.
Control Module References for scan tool information
Ignition ON, place the blower switch in the Low, Medium 1, Medium 2 and High speed positions. The blower motor should operate in each speed position.
⇒ | If the blower motor is inoperative at all speeds, refer to Blower Motor Inoperative. |
⇒ | If the blower motor functions at a single speed only, refer to Blower Motor Malfunction. |
⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or 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. |
⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
⇒ | If the test lamp does not illuminate, replace the BCM. |
⇒ | If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the HVAC relay. |
⇒ | If greater than the specified range, test the control circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
• | Low control terminal D |
• | M1 control terminal A |
• | M2 control terminal B |
• | High control terminal C |
⇒ | If the test lamp does not illuminate, test the appropriate control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
⇒ | If the resistance is not within the specified range, replace the relay. |
• | 30 and 86 |
• | 30 and 87 |
• | 30 and 85 |
• | 85 and 87 |
⇒ | If not the specified value, replace the relay. |
⇒ | If greater than the specified range, replace the relay. |
⇒ | If the blower motor does not activate, replace the blower motor. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for HVAC control module replacement, setup, and programming |