P0CD5: Hybrid/EV Battery Pack Coolant Temperature Sensor B Circuit
What to do
As P0C42 and P0CD5. The useful number is the difference between inlet and outlet — if they read almost the same while the pack is working, coolant is not moving even if the pump sounds like it is.
What this code means
The pack's second coolant temperature sensor has a circuit fault.
Sensor A is at P0C42, where the argument lives: coolant temperature is a different question from cell temperature, and the diagnosis is the gap between them.
What a second sensor adds is the direction of flow. One at the pack's inlet and one at its outlet turns two readings into a measurement: the difference between them is the heat actually being carried away. A large gap means the coolant is doing its job; almost no gap means the coolant is not moving, whatever the pump is being told to do — and that is exactly the fault an airlock produces while everything electrical tests perfectly.
So losing this sensor does not merely remove a number. It removes the only direct evidence the cooling system is working.
Likely causes
Start here
- Faulty engine coolant temperature sensor · moderate
- Corroded or loose connector · easy
Less common
- Low coolant level · easy
- Coolant leak into the sensor connector · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0CD5.