P0A97 – Hybrid Battery Pack Cooling Fan 2 Control Circuit

P0A97 – Hybrid Battery Pack Cooling Fan 2 Control Circuit is a diagnostic trouble code that signals an electrical fault in the control circuit responsible for operating Hybrid Battery Cooling Fan 2. Unlike “Low” (P0A95) or “High” (P0A96) variants, P0A97 indicates a general malfunction—meaning the ECU cannot reliably command or monitor Fan 2. Because this fan helps regulate hybrid battery temperature during moderate-to-high cooling demands, any loss of control can lead to overheating, reduced hybrid performance, or battery protection modes. This guide explains what P0A97 means, what causes it, how to diagnose it, and the repairs that solve it.

What Does P0A97 Mean?

P0A97 is a generic SAE J2012-DA hybrid/EV code. The Battery Energy Control Module (BECM) or Hybrid Control ECU sets this code when it detects abnormal operation in the Fan 2 control circuit—such as missing feedback, erratic voltage, unstable PWM signals, or intermittent response. Fan 2 typically engages during higher battery temperature conditions or when Fan 1 alone cannot maintain adequate airflow.

A fault in this circuit means the ECU cannot properly command Fan 2, which compromises hybrid battery cooling efficiency. If unresolved, overheating may reduce battery lifespan or trigger limp mode.

Quick Reference

  • OBD-II Family: P0xxx – Hybrid/EV Battery & Cooling Systems
  • Scope: Generic (SAE J2012-DA)
  • System: Hybrid Battery Cooling Fan Control
  • Difficulty Level: Medium
  • Estimated Repair Cost: €150–€900
  • Last Updated: 2025-12-08

Real-World Example / Field Notes

I’ve seen P0A97 often on Toyota Prius, Auris, CT200h, and Yaris Hybrid models. One Prius owner complained of weak EV performance on hot days. Fan 2 would intermittently shut off during operation, causing the hybrid battery to climb in temperature. The root cause was a partially broken wire in the rear quarter panel harness—flexed every time the vehicle hit bumps. The fan wasn’t receiving a stable command signal, triggering P0A97. Repairing the wire and cleaning the connector resolved the issue. Cooling fan problems are frequently wiring-related rather than motor-related.

Symptoms of P0A97

  • Check Hybrid System warning: Often appears shortly after the fault occurs.
  • Intermittent fan operation: Fan 2 may run inconsistently or not at all.
  • Reduced EV mode functionality: Battery protection logic disables EV mode.
  • Elevated battery temperatures: Temperature climbs under load or warm weather.
  • Reduced acceleration: The hybrid ECU limits output to protect the battery.
  • Unusual fan noises: Surging or inconsistent fan speed behavior.

Common Causes of P0A97

Most Common Causes

  • Faulty Hybrid Battery Cooling Fan 2 (motor failure or intermittent operation).
  • Damaged wiring harness or broken control wires.
  • Corrosion at Fan 2 connectors due to moisture or debris.
  • Fan speed driver transistor malfunction (internal to some fan modules).
  • Power supply instability from a failing relay or fuse issue.

Less Common Causes

  • Hybrid Battery ECU output driver failure.
  • Fan 2 ground circuit resistance or poor grounding point.
  • Aftermarket wiring interfering with rear duct wiring channels.
  • Obstructed ducts increasing fan load and causing circuit abnormalities.
  • Temperature sensor irregularities causing incorrect fan logic.

Diagnosis: Step-by-Step Guide

Start your diagnosis by verifying Fan 2 activation commands and checking for stable voltage at the control wire.

Tools You’ll Need: OBD-II hybrid scan tool, multimeter, back-probe pins, wiring diagrams, cleaning tools, and access to rear cooling duct components.

  1. Inspect the cooling ducts. Blocked airflow forces the fan to work harder and can distort circuit readings.
  2. Activate Fan 2 with a scan tool. Observe whether the fan runs, pulses, or fails completely.
  3. Measure control voltage at the fan connector. Irregular or missing voltage indicates wiring or driver issues.
  4. Back-probe the ECU side of the circuit. Confirms whether the issue is upstream or downstream.
  5. Check continuity and ground. Weak or intermittent grounds commonly cause unstable fan control.
  6. Inspect connectors for corrosion or moisture. This is a frequent cause in vehicles with leaks or high humidity.
  7. Test the fan motor. Check motor resistance and spin smoothness; intermittent motors often set P0A97.
  8. Test the fan driver transistor or module. Voltage drop across the module reveals internal failures.
  9. Monitor battery temperature during a road test. Inconsistent temperature response suggests fan control issues.
  10. Evaluate Hybrid Battery ECU output. If all wiring and components are good, ECU output logic may be failing.

Pro Tip: Use Mode $06 to check fan performance monitors. These test values often show intermittent or unstable fan behavior long before complete failure.

Possible Fixes & Repair Costs

  • Repair damaged wiring or connectors – Resolves most intermittent control faults; €80–€200.
  • Replace Hybrid Battery Cooling Fan 2 – Fixes motor-related failures; €250–€600.
  • Replace fan driver transistor/module – Corrects unstable voltage control; €150–€350.
  • Clean or repair cooling ducts – Improves airflow and reduces fan load; €50–€120.
  • Replace fan relay or repair fuse circuit – Restores stable power delivery; €50–€150.
  • Replace Hybrid Battery ECU – Only if all other causes are ruled out; €300–€700.

Always isolate the exact source of the control failure before replacing expensive hybrid components.

Can I Still Drive With P0A97?

Short trips may be possible, but caution is advised. Without reliable Fan 2 operation, the hybrid battery may overheat during moderate or heavy load conditions. The vehicle may disable EV mode or reduce power to protect battery health. Prolonged driving with this code can accelerate battery wear and lead to unexpected hybrid system shutdown.

Related Codes

  • P0A6C – Hybrid Battery Voltage System Isolation Sensor Range/Performance
  • P0A9F – Hybrid Battery Temperature Sensor Too Hot
  • P0A9E – Hybrid Battery Temperature Sensor Too Cold
  • P0A9D – Hybrid Battery Temperature Sensor Range/Performance
  • P0A9C – Motor Electronics Coolant Temperature Sensor Circuit High
  • P0A9B – Motor Electronics Coolant Temperature Sensor Circuit Low
  • P0A9A – Motor Electronics Coolant Temperature Sensor Circuit Range/Performance
  • P0A99 – Motor Electronics Coolant Temperature Sensor Circuit
  • P0A98 – Hybrid Battery Pack Cooling Fan 2 Performance
  • P0A96 – Hybrid Battery Pack Cooling Fan 2 Control Circuit High

Key Takeaways

  • P0A97 indicates a general malfunction in the Hybrid Battery Cooling Fan 2 control circuit.
  • Wiring faults, connector corrosion, and fan driver failures are the most common causes.
  • Uncontrolled fan operation can lead to battery overheating and reduced performance.
  • Diagnose wiring and control circuits carefully before replacing components.

FAQ

How do I fix P0A97?

Begin by checking wiring, connectors, and verifying Fan 2 operation with a scan tool. Most cases involve intermittent wiring faults or a failing fan motor. Repair the circuit and replace components as needed to restore stable fan control.

Can blocked ducts cause P0A97?

Yes. While the code refers to the control circuit, duct restriction increases fan load, which can trigger circuit instability or overheating. Cleaning the ducts is an essential part of diagnosing cooling issues.

Is it safe to drive with P0A97?

Short distances may be okay, but the hybrid battery is at risk of overheating without proper fan control. Power reduction or EV mode shutdown can happen unexpectedly. Repair the issue soon.

Does P0A97 mean the battery is bad?

No. It refers to the cooling fan circuit, not the battery itself. However, unresolved fan issues can shorten battery life by allowing higher-than-normal operating temperatures.

Can aftermarket wiring cause P0A97?

Absolutely. Poorly routed audio cables or accessory wiring often damage or interfere with the cooling fan harness, leading to unstable control signals and triggering this code.