P0A99

Code

Generic P — Powertrain

Hybrid/EV Battery Pack Cooling Fan 2 Control Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 23 EN: 38 RU: 37

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Damaged, corroded, or loose wiring or connector for fan 2
Short to ground or short to voltage in the fan control circuit
Failed battery pack cooling fan motor (fan 2)
Blown fuse or faulty relay in the fan supply/control circuit
Faulty fan control module / battery management / hybrid control ECU
High-resistance connection (poor ground) or connector contamination

Symptoms

Battery pack cooling fan 2 does not run when commanded
Reduced or no battery pack cooling at certain conditions
Warning light or message related to battery cooling or hybrid system
Possible thermal events (fan runs only intermittently) or reduced HVAC/battery performance
Related diagnostic trouble codes for other fan circuits or battery temperature sensors

What to check

Read freeze-frame and live data with a diagnostic scanner; confirm P0A99 and any related codes
Visually inspect fan 2 wiring harness, connectors, and pin condition for corrosion, heat damage, or disconnection
Check the cooling fan 2 fuse(s) and any related relays; verify proper fuse value and continuity
Attempt a bi-directional / actuator test (command fan 2 ON) from the scan tool and observe operation
Listen/observe fan operation during commands; check for mechanical obstruction or seized motor
Measure voltage at the fan connector (supply and control pins) with harness connected and disconnected

Signal parameters

Supply voltage to fan motor (typical 12 V system): ~11–15 V when key ON / supply present
Control signal: either switched low (near 0 V) or PWM from controller — PWM frequency commonly 50–1000 Hz depending on vehicle; duty cycle varies with command
Expected motor winding resistance (typical range): ~0.5–10 ohms (varies by fan design) — compare to manufacturer spec
Expected current draw while running: typically 1–10 A for 12 V cooling fans (verify vehicle spec)
When commanded ON, control module output should show change (PWM or switched ground) rather than a constant low-voltage fault

Diagnostic algorithm

Retrieve codes and live data; record freeze-frame and related DTCs. Verify ignition state and any conditions required for the fault to set.
Visually inspect the fan assembly, harness, and connectors for damage, corrosion, or loose pins. Repair any visible problems.
With ignition OFF, check fuses and relays for the fan circuit. Replace any blown fuses and retest.
Use the scan tool to command fan 2 ON. Observe whether the fan runs. If it runs reliably on command, check for intermittent wiring or control signal issues under varying conditions.
If fan does not run on command, disconnect the fan connector and measure supply voltage at the harness: verify battery/12 V supply is present (11–15 V) at the supply pin.
Measure control/driver pin at the harness while commanding ON: verify the control module produces the expected PWM or switching signal. If no control signal, suspect control module or wiring to it.
With connector disconnected, measure motor winding resistance and inspect for continuity; if open or shorted, replace fan motor assembly.
Check ground continuity from the fan ground to chassis negative. Repair any high-resistance ground connections.
If supply and ground are good at the connector but motor does not run when powered directly from a known good 12 V source, replace the fan motor.
If direct-power test runs the fan but control module output is missing or shorted, trace wiring back to the module, check for shorts to ground or battery voltage, and test/replace the driver module per manufacturer procedure.
After repairs, clear codes, perform functional tests (bi-directional commands and road/test conditions), and verify the code does not return.

Likely causes

Open or shorted wiring/connector to fan 2 (most common)
Failed fan motor (stalled or open winding)
Blown fuse or failed fan relay/power device
Faulty fan driver in the control module
Poor ground or high-resistance connection

Fault status

⚠️ Status

P0A99 — Hybrid/EV Battery Pack Cooling Fan 2 Control Circuit Low. Possible wiring, fuse/relay, fan motor, or control module fault. Inspect wiring/connectors and test fan operation.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours