P0E13: Hybrid/EV Battery Pack Coolant Heater A Control Circuit Low
What to do
You may notice nothing until the weather turns cold. Then expect reduced range, weak acceleration, little regenerative braking and slow rapid charging — and note that this looks exactly like a worn-out battery. If the car is normal in warm weather, it is not the pack. Preconditioning while still plugged in helps in the meantime.
What this code means
The control circuit for the traction battery's coolant heater is faulty.
A traction battery has a heater, and most people do not know it — including a lot of the people who diagnose them.
A lithium pack works badly cold, and the reason is physical rather than electronic: the lithium ions move through the electrolyte more slowly at low temperature, so the pack's internal resistance rises steeply. Below about ten degrees the car must limit both how much power it takes out and how much it puts in — which is why an electric car in winter is slower, has less regenerative braking and rapid-charges at a fraction of its summer rate. The argument for why forcing charge into a cold pack is genuinely damaging is at P0CA6.
So the car heats the pack, using a coolant heater in the battery's thermal circuit, typically before a scheduled departure and while preconditioning for a rapid charge. This is the code family for that heater.
Its failure is invisible for half the year and then transforms the car. Summer: nothing. Winter: reduced range, weak acceleration, no regenerative braking for the first miles, and a rapid charger delivering a fraction of its rating — on a vehicle with no other fault, whose owner concludes the battery is worn out. A heater fault and a genuinely aged pack present almost identically in January, and the discriminator is what happens in July.
At or below the lower limit, usually a short to earth.
Likely causes
Start here
- Failed battery coolant heater · specialist
- Open circuit in control wiring · specialist
- Corroded or loose connector · specialist
Less common
- Control module driver failure · specialist
- Damaged wiring harness · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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