SureTrack Real Fix: A Gust of Knowledge

SureTrack “The only source of knowledge is experience” – Albert Einstein. Real Fixes are constructed from an actual occurrence within a shop. SureTrack users gain insight on automotive repairs by viewing the diagnosis of other technicians. In this specific situation, the technician’s experience entailed a blower motor that was operating when the key was in the off position.

Educate yourself by analyzing this Real Fix and doing away with that unwanted gust of wind from the blower vents.

Vehicle
2003, BMW 530i, 3.0L

Title
Dead Battery, Replaced Blower Motor Resistor

Complaint
The customer states the vehicle will not start.

Cause
Confirmed the customer's complaint and found the vehicle did not start. Connected the vehicle to a battery charger, charged the battery, and proceeded with diagnosing the no start complaint. Used the battery conductance tester to test the battery, and found the battery was able to conduct the specified amount of current, which verified it operated properly. Ran the engine, raised the engine speed to 1,500 RPM, and used a multi-meter to measure the charging system voltage across the battery terminals. The measured voltage present at the battery was within the specified range, which verified the charging system operated properly. Disconnected the battery negative cable and connected the multi-meter between the battery negative cable and battery negative terminal. Key off, allowed the vehicle to enter sleep mode, monitored the multi-meter amperage reading, and observed the amperage reading was greater than the allowable specification. This indicated a parasitic draw was present. Entered the vehicle and noticed the blower motor operated when the key was in the off position. Removed the interior knee panel, disconnected the blower motor resistor connector, and observed the measured amperage on the multi-meter dropped to an allowable limit. Reconnected the blower motor resistor connector and used the multi-meter to measure voltage at the connector. Observed voltage was delivered to the blower motor with the air conditioning switch in the "off" position. This indicated the blower motor resistor was internally faulty and caused the blower motor to operate at all times, which caused the vehicle's battery to discharge.

Correction
Replaced the blower motor resistor and verified the vehicle operated properly. The customer's concern did not return.


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