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Tahoe / Yukon Service Manual

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
2042 B+ B2B01 B2B01 — —
754 Control B2B01 B2B01 B2B00 B2AFF
761 Signal B2B02 B2B02 B2B03 B2B0B, B2B0C
1050 Ground — 1 — —
1. Blower Motor Malfunction

Circuit/System Description The blower motor speed control signal from the body control module, battery positive and ground circuits enable the blower motor to operate. The blower motor control circuitry is integrated within the blower motor assembly. The body control module provides a ground pulse width modulation (PWM) signal to the blower motor to request a specific motor speed. The blower motor translates the PWM signal and drives the motor accordingly. Diagnostic Aids The design of this motor does not allow for bench testing. The motor will not operate by simply applying power and ground. Inspect the motor shaft for rust or other foreign material which may prohibit proper motor operation. Check for Preliminary Information or Technical Service Bulletins. 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

  1. Ignition OFF and all vehicle systems OFF, disconnect the connector at the M8 Blower Motor. It may take up to 10 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 6 and ground. ⇒ If 10 Ω or greater Repair the open/high resistance on circuit 1050 or the ground connection. ⇓ If less than 10 Ω
  3. Verify a test lamp illuminates between the B+ circuit terminal 1 and ground. ⇒ If the test lamp does not illuminate and the circuit fuse is good Repair the open/high resistance on circuit 2042. ⇒ If the test lamp does not illuminate and the circuit fuse is open 3.1. Test circuit 2042 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. Replace the M8 Blower Motor. ⇓ If the test lamp illuminates
  4. Ignition ON.
  5. Test for less than 1 V between the control circuit terminal 2 and ground. ⇒ If 1 V or greater 5.1. Test circuit 754 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 5.2. Replace the K9 Body Control Module
  6. Ignition OFF. It may take up to 10 min for all vehicle systems to power down.
  7. Test for infinite resistance between the control circuit terminal 2 and ground. ⇒ If less than infinite resistance 7.1. Test circuit 754 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 7.2. Replace the K9 Body Control Module ⇓ If infinite resistance
  1. Ignition OFF, connect the connector at the M8 Blower Motor. Ignition ON.
  2. While backprobing terminal 2 at the M8 Blower Motor, test for greater than 1 V between control circuit and ground. ⇒ If 1 V or less Replace the M8 Blower Motor. ⇓ If greater than 1 V
  3. Verify the voltage decreases and increases while using the controls to change the blower speed selection. ⇒ If the voltage does not decrease and increase as the blower speed selection is changed 10.1. Test circuit 754 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 10.2. Replace the K9 Body Control Module ⇓ If the voltage decreases and increases as the blower speed selection is changed
  4. Replace the M8 Blower Motor. 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