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DTC codes / P2Bxx · Hybrid propulsion / P2B31

P2B31Fan 2 Performance/Stuck Off

P2B31 is a generic powertrain code indicating that the powertrain control module (PCM) has detected a performance fault with the second cooling fan circuit, specifically that the fan is stuck off or not achieving the commanded speed. The PCM commands the fan on and monitors the circuit or fan feedback, and when the expected response is not seen within a calibrated time, it sets this code.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • Engine coolant temperature may run higher than normal, especially in traffic or hot weather.
  • The cooling fan may not turn on when the air conditioning is switched on.
  • Possible overheating warning message or gauge reading high if the fault persists.
  • Reduced air conditioning performance due to lack of condenser airflow.
  • In some vehicles, the fan may run continuously at full speed as a failsafe.

Common causes, most likely first

  1. Failed cooling fan motor or fan assembly (seized, open winding, or worn brushes).
  2. Blown fuse or fusible link in the fan power circuit.
  3. Damaged or corroded wiring, connectors, or ground connections at the fan or relay.
  4. Faulty fan relay or fan control module.
  5. PCM internal driver failure or software issue.
  6. Mechanical obstruction preventing fan rotation (debris, damaged shroud).
  7. Low coolant level or air pockets causing inaccurate temperature readings and fan command issues.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in other modules.
  2. Inspect the cooling fan fuse and relay, and test the relay operation.
  3. Perform a visual inspection of the fan wiring, connectors, and ground points for damage or corrosion.
  4. Command the fan on using the scan tool bidirectional controls and observe if the fan runs.
  5. Test the fan motor directly by applying power and ground to confirm it operates.
  6. Check the coolant level and bleed the cooling system if necessary to ensure proper temperature sensor readings.
  7. If all electrical and mechanical checks pass, diagnose the PCM driver circuit and replace the PCM if faulty.

Fan 2 Stuck Off: Common Misdiagnosis Traps

  • A fan that spins freely by hand can still be electrically faulty, so always test the motor with a direct power source before condemning the PCM.
  • Corroded ground connections on the fan motor or chassis are a frequent cause that is often overlooked during visual inspection.
  • Some vehicles use a fan control module that receives a pulse-width modulated (PWM) signal; a failed module can mimic a stuck-off fan.
  • The code may set intermittently if the fan only fails under certain conditions, such as high ambient temperature or after extended idle.
  • After replacing a fan motor, clear the code and verify the fan operates through several drive cycles to ensure the repair is complete.

Can I keep driving with P2B31?

It is generally safe to drive short distances with this code, but monitor the engine temperature closely and avoid heavy traffic or hot weather until repaired. If the temperature gauge climbs above normal, pull over and shut off the engine to prevent damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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