Diagnostic Instructions
| • | 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. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Coolant ByPass Valve Solenoid Control | 1 | 1 | -- | -- |
Coolant ByPass Valve Solenoid Ground | -- | 1 | 1 | -- |
1. Auxiliary Air Temperature Malfunction | ||||
Circuit/System Description
The purpose of the auxiliary heating system is to supply heat to the rear interior of the vehicle. The heater auxiliary blower motor switch is located on the headliner and controls the auxiliary blower motor speeds for rear heater operation. Placing the heater auxiliary blower motor switch in any position other than OFF, turns on the solenoid allowing vacuum to open the water valve, this action allows coolant to flow through the auxiliary heater core. The location of the hot water shut off valve is under the right rear area of the cab. The only way to regulate the temperature of the air is to regulate the blower speed.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Ignition ON, engine running, place the auxiliary blower switch in the LO, MED and HI speed positions. The auxiliary motor should activate and operate from low to medium to high when changing between the commanded states.
| ⇒ | If the blower motor speed does not change or fails to operate at a selected speed, refer to Auxiliary Blower Motor Malfunction . |
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the coolant bypass valve solenoid.
- Test for less than 1.0 ohm between the ground circuit terminal B and ground.
- Ignition ON, verify that a test lamp illuminates between the control circuit terminal A and ground.
- If all circuits test normal, test or replace the coolant bypass valve solenoid.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit test normal, test or replace the auxiliary HVAC control assembly. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
