P0C1B: Electric/Auxiliary Transmission Fluid Pump Control Module Internal Temperature Too High
What to do
If the car thumps pulling away from traffic lights on hot days and behaves perfectly when cool, mention exactly that — a heat-related fault in this module reproduces only when hot, and a workshop testing a cold vehicle will find nothing at all. Low or degraded transmission fluid makes it worse by carrying less heat away, so fluid condition is worth checking early and is cheap.
What this code means
The auxiliary transmission fluid pump's control module has reported its own internal temperature as too high.
A module measuring itself is unusual enough to be worth explaining. This one does it because of where it lives: the electronics that drive the pump are mounted on or inside the transmission, which is one of the hottest places on the vehicle and gets hotter precisely when the pump is working hardest.
So the module protects itself, and the consequence lands on the transmission rather than on the electronics: the pump stops, and the gearbox loses the line pressure it depends on whenever the engine is off. Everything at P0B00 returns — a thump or a hesitation pulling away from rest, stop-start declining to work, electric driving refused — but now intermittently and in hot weather, which makes it far harder to recognise.
A summer-only version of the P0B00 symptoms is this code until proved otherwise, and it is worth saying so because the pump itself will test perfectly on a cold morning.
Likely causes
Start here
- Low or degraded transmission fluid · easy
- Faulty auxiliary transmission fluid pump · specialist
Less common
- Blocked or restricted transmission fluid cooler · moderate
- Sustained heavy load on the electric motor · 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 P0C1B.