Auxiliary Blower Motor Malfunction
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 Number | Circuit Function | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performan |
|---|---|---|---|---|---|
| 1740 | B+ | 1 | 1 | — | — |
| 101 | B+ | 1 | 1 | — | — |
| 2211 | Control | 1 | 1 | 1 | - |
| 5988 | Control | 2 | 1 | 1 | — |
| 1450 | Ground | - | 1 | - | - |
| 1. Rear blower motor inoperative. 2. Rear blower motor operates on high speed at all times |
Circuit/System Description The K8AB Blower Motor Control Module- Rear is an interface between the A34 Heater and Air Conditioning Auxiliary Control and the M8B Blower Motor - Rear. The K8AB Blower Motor Control Module- Rear has 5 circuits: a B+ input, ground, a control signal from the A34 Heater and Air Conditioning Auxiliary Control, a B+ output and a low side pulse width modulation (PWM) control to the M8B Blower Motor - Rear. The A34 Heater and Air Conditioning Auxiliary Control provides a low side (PWM) signal to the K8AB Blower Motor Control Module- Rear in order to request the M8B Blower Motor - Rear speed. The K8AB Blower Motor Control Module- Rear grounds the blower motor using a low side PWM signal in order to vary the motor speed. Diagnostic Aids Inspect the motor shaft for rust or other foreign material which may prohibit proper motor operation. Reference Information Schematic Reference HVAC Schematics Connector End View Reference Master Electrical Component List Description and Operation Automatic HVAC Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References for scan tool information Circuit/System Testing
- Ignition OFF and all vehicle systems OFF, disconnect the X2 harness connector at the K8AB Blower Motor Control Module - Rear. It may take up to 10 min for all vehicle systems to power down.
- Test for less than 10 Ω between the ground circuit terminal 4 and ground. ⇒ If 10 Ω or greater Repair the open/high resistance on circuit 1450 or the ground connection. ⇓ If less than 10 Ω
- Verify a test lamp illuminates between the B+ circuit terminal 2 and ground. ⇒ If the test lamp does not illuminate and the circuit fuse is good 3.1. Test circuit 1740 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 3.2. Verify the fuse is not open and there is voltage at the fuse. ⇒ If the test lamp does not illuminate and the circuit fuse is open 3.1. Test circuit 1740 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 3.2. Disconnect the X1 harness connector at the K8AB Blower Motor Control Module - Rear and disconnect the harness connector at the M8B Blower Motor - Rear. 3.3. Test circuit 101 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 3.4. Test or replace the M8B Blower Motor - Rear. ⇓ If the test lamp illuminates
- Ignition ON. Test for less than 1 V between the control circuit terminal 3 and ground. ⇒ If 1 V or greater 4.1. Test circuit 2211 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found 4.2. Replace the A34 Heater and Air Conditioning Auxiliary Control ⇓ If less than 1 V
- Ignition OFF. It may take up to 10 min for all vehicle systems to power down.
- Verify a test lamp does not illuminate between the control circuit terminal 3 and B+. ⇒ If the test lamp illuminates 6.1. Test circuit 2211 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 6.2. Replace the A34 Heater and Air Conditioning Auxiliary Control ⇓ If the test lamp does not illuminates
- Ignition OFF, connect the X2 harness connector at the K8AB Blower Motor Control Module - Rear. Ignition ON.
- While backprobing terminal 3 X2 at the K8AB Blower Motor Control Module - Rear, test for greater than 1 V between control circuit and ground. ⇒ If less than 1 V Replace the K8AB Blower Motor Control Module - Rear. ⇓ If 1 V or greater
- Verify the voltage decreases and increases while using the controls to change the rear blower speed selection. ⇒ If the voltage does not decrease and increase as the blower speed selection is changed 9.1. Test circuit 2211 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 9.2. Replace the A34 Heater and Air Conditioning Auxiliary Control ⇓ If the voltage decreases and increases as the blower speed selection is changed
- Ignition OFF, disconnect the X1 harness connector at the K8AB Blower Motor Control Module - Rear.
- Connect a test lamp between the B+ terminal 1 X1 and the control circuit terminal 2 X1 at the K8AB Blower Motor Control Module - Rear, ignition ON and blower ON.
- Verify the test lamp increases and decreases in brightness while using the controls to change the rear blower speed selection. ⇒ If the test lamp does not illuminate, or does not increase and decrease in brightness as the blower speed selection is changed Replace the K8A Blower Motor Control Module – Auxiliary. ⇓ If the test lamp increases and decreases in brightness as the blower speed selection is changed
- Test or replace the M8B Blower Motor – Auxiliary. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. HVAC Component Replacement Reference Control Module References for control module replacement, programming and setup