• | 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 |
---|---|---|---|---|
Relay Coil Ignition | 2 | 2 | -- | -- |
Relay Switch B+ | 2 | 2 | -- | -- |
Auxiliary Blower Motor Resistor Low Speed Control | 1 | 1 | 1 | -- |
Auxiliary Blower Motor Resistor Medium Speed Control | 1 | 1 | 1 | -- |
Relay Controlled Output | 2 | 2 | 1 | -- |
Auxiliary Blower Motor Control | 2 | 2 | 1 | -- |
Auxiliary Blower Motor Ground | -- | 2 | 2 | -- |
Relay Coil Ground | -- | 2 | 2 | -- |
1. Auxiliary Blower Motor Malfunction 2. Auxiliary Blower Motor Inoperative |
Voltage is supplied to the auxiliary heater blower motor switch from the auxiliary blower motor relay. The auxiliary HVAC control assembly applies voltage to the auxiliary 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 auxiliary blower motor per particular speed request:
• | Low speed-2 resistors |
• | Medium speed-1 resistor |
When the operator requests High speed, voltage is applied directly to the auxiliary heater blower motor.
Control Module References for scan tool information
Ignition ON, place the auxiliary blower switch in the LO, MED and HI speed positions. The blower motor should operate in each speed position.
⇒ | 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. If the circuit tests normal and the ignition circuit fuse/circuit breaker is open, test or replace the auxiliary blower motor relay. |
⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit breaker is open, test the output circuit terminal 87 for a short to ground. |
⇒ | If the test lamp does not illuminate, test the output circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor relay. |
• | LO - terminal C |
• | MED - terminal A |
• | HI - terminal B |
⇒ | 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, test or replace the auxiliary HVAC control assembly. |
⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the blower motor resistor assembly. |
⇒ | If the test lamp does not change intensity, test the control circuit for a short to voltage. If the circuit tests normal, test or replace the blower motor resistor assembly. |
⇒ | 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 auxiliary blower motor. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.