What it means
The hybrid battery cooling system C does not maintain target temperatures under load. Coolant flow, radiator fouling, or pump output reduced on this branch.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The battery management system monitors temperatures and cooling performance on hybrid/EV battery cooling branch C under load. P2D40 sets when branch C does not keep the battery within its target temperature range, potentially because of restricted heat rejection, reduced pump flow, or pack imbalance.
Common causes
Most likely first.
- Radiator fins fouled - reduced heat rejection
- Pump output degraded with age
- Pack cell imbalance approaching service threshold
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
How to diagnose it
- Record freeze-frame data and compare battery temperatures, cooling requests, and pump commands when branch C performance is flagged.
- Inspect branch C radiator or heat exchanger fins and the surrounding air path for fouling, obstruction, or damage.
- Check the branch C coolant level and accessible hoses and connectors for leaks, kinks, or loose connections.
- Use scan-tool data or supported active tests to compare branch C pump operation and temperature change with the other cooling branches.
- Test the branch C pump and wiring, then check pack cell balance if the cooling hardware passes inspection.
Common fixes
- Clean debris from the branch C heat exchanger and restore airflow.
- Repair a leaking, kinked, or poorly connected branch C hose or connector.
- Repair damaged pump wiring or connections.
- Replace the branch C pump if it fails the manufacturer's performance check.
- Address battery cell imbalance if data shows it is contributing to localized heating.
Can I keep driving?
Limit driving and avoid heavy acceleration, towing, and repeated fast charging because branch C may not remove battery heat effectively. Stop if a battery temperature warning appears or power drops sharply, since continued overheating can trigger stronger power limits or damage the pack.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.