P0A9A

Code

Generic P — Powertrain

Hybrid/EV Battery Pack Cooling Fan 2 Control Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 27 EN: 43 RU: 28

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Page language: EN

Causes

Open or intermittent wiring in the Fan 2 control circuit
Short to battery/auxiliary voltage on the control wire
Corroded or poorly seated connector at fan assembly or control module
Failed cooling fan motor or internal short in fan assembly
Faulty fan driver inside inverter/ECU/Battery Management Module
Blown or shorted relay or fuse associated with fan control

Symptoms

Battery pack temperature warning or battery thermal management fault
Cooling fan 2 may run continuously, at full speed, intermittently, or not run at all
Reduced charge rate or vehicle limiting performance due to battery thermal protection
DTC present and possibly stored freeze-frame data
Unusual fan noise (if motor partially failing) or no audible fan operation

What to check

Follow vehicle-specific high-voltage safety and isolation procedures before any inspection or measurement.
Read freeze-frame and live data with a capable scan tool (fan command, duty cycle, measured control voltage, related thermal sensors).
Visually inspect wiring harnesses and connectors for damage, corrosion, pin backing-out or water ingress at fan 2 and control module.
Check fuses and relays related to battery cooling fans and auxiliary supplies.
Backprobe/measure control circuit voltage and PWM signal at the fan connector and at the controlling module with the system in the same operating condition as the fault.
Measure resistance of the fan motor windings per service manual with power isolated.

Signal parameters

Expected control signal: low-voltage logic/PWM or switched ground depending on vehicle (consult service manual).
Normal idle/control voltage typically near 0 V when off or a 0–12 V PWM range depending on design; consult manufacturer values.
High condition: control circuit voltage measured near supply voltage or an unexpected steady high voltage compared to expected command.
Motor winding resistance: consult service manual; typical low-resistance value for brushless/DC blower motors (measured with power off) — if infinite or shorted, motor likely faulty.
Live-data parameters: commanded duty cycle vs. actual measured voltage/duty; abnormal mismatch suggests wiring or driver fault.

Diagnostic algorithm

Safety: Disable high-voltage system per manufacturer procedure and isolate the vehicle before inspecting or measuring HV components.
Scan tool: Retrieve codes, freeze-frame, and live data (fan command, actual fan voltage/duty, battery temp). Note when code set and operating conditions.
Visual inspection: Check connectors and wiring for damage, water, corrosion, pin issues at Fan 2 and controlling module. Repair any obvious damage.
Verify power/ground: With the system safely powered as required by service manual, backprobe the fan control connector to measure control voltage/PWM while commanding fan on/off from the scan tool. Compare to expected values.
Check for short to voltage/ground: With ignition off and high-voltage isolated per manual, use a multimeter to check continuity between the control wire and supply voltage/ground to identify short or open circuits.
Motor resistance test: With power isolated, measure fan motor winding resistance and compare to spec. If out of range (open or shorted), replace the fan motor/assembly.
Bench test fan: If safe and allowed by procedure, apply bench power to the fan motor per service instructions to confirm operation, bearing noise, or shorts (avoid connecting HV components without proper isolation).
Swap/replace suspected components: If wiring and motor test OK, suspect driver module (inverter/ECU/BMU). Confirm by testing output at module and consider module replacement only after verifying external wiring and load.
Repair wiring/connectors or replace faulty fan or module. Clear codes and perform full-system functional test including temperature-based fan operation and a road or controlled test to confirm resolution.
If code returns, escalate to module-level diagnostics per manufacturer procedures or consult technical service bulletins.

Likely causes

Disconnected or damaged connector at Fan 2 motor resulting in the circuit being pulled to supply voltage
Wire chafing contacting a supply rail producing a high voltage reading
Failed fan motor winding creating abnormal circuit behavior
Internal driver (inverter/ECU/BMU) fault forcing the control output high
Corroded pins or high-resistance connection causing erratic voltages