B2580

Code

Other B — Body

Aux Blower Sense Switch Circuit Failure

Brand: Other

Type: B — Body

Views: UK: 27 EN: 57 RU: 35

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Open or short in the aux blower sense switch wiring (to ground or battery)
Faulty auxiliary blower sense switch or speed sensor
Poor connector contact or corrosion at the sensor, module, or harness connector
Blown fuse or failed blower relay affecting reference voltage or ground
Faulty HVAC control module, BCM, or wiring harness damage (pinched, chafed, rodent)
Intermittent wiring or connector damage due to vibration or moisture

Pull and visually inspect connectors at the auxiliary blower and HVAC/control module for corrosion, bent pins, damage or water intrusion
Check relevant fuses and relays for continuity and proper operation
Scan for additional HVAC/body codes and freeze frame data
With key ON (engine off), backprobe the sense switch connector and measure reference voltage and signal
Wiggle the harness while observing live data/voltage for intermittent faults
Inspect blower motor and resistor assembly for signs of overheating or damage

Reference voltage: typically a stable 5 V reference from the control module (verify exact value in service manual)
Signal voltage: expected 0–5 V analog or a pulsed/PWM feedback signal depending on design (consult wiring diagram)
Continuity: closed switch or low-resistance sensor path should show low ohms to ground or signal return when activated; open circuit indicates broken wiring/switch
When suspecting PWM, use an oscilloscope or wave-capable meter to confirm pulse frequency and duty cycle (refer to service manual)

Connect a diagnostic scan tool, retrieve freeze frame and related codes, and note when the fault occurred.
Visually inspect connectors, wiring harness, and blower assembly for damage, corrosion, or water ingress. Repair any obvious issues.
Verify fuses and relays in the blower/HC circuits. Replace suspected faulty items and recheck.
With ignition ON, backprobe the sense switch connector: verify reference voltage (usually ~5 V) from the HVAC/BCM, a good ground, and the signal voltage. Compare to expected values in the repair manual.
Check continuity between the sense switch and control module pins. Repair any open or high-resistance circuits. Check for shorts to ground or battery.
If the signal is PWM, capture waveform with an oscilloscope and compare frequency/duty to specifications.
If wiring and connectors are good but signal still out of range, bench-test or replace the auxiliary blower sense switch/sensor or blower assembly as specified by manufacturer procedures.
If component replacement does not restore proper signal, inspect or replace the HVAC control module/BCM per manufacturer diagnostic flow.
Clear codes and perform a functional test of the blower across speeds and repeat driving or operation conditions to confirm repair.