P07CB
Transmission Fluid Thermostat Performance
The transmission fluid thermostat (similar in function to a coolant thermostat — opens at a calibrated temperature to route ATF through the cooler) does not regulate temperature within the expected band. Either stuck open (ATF stays cold, friction modifier ineffective) or stuck closed (ATF overheats, oxidising the fluid).
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Common causes
Ordered by how often each turns out to be the cause.
- Thermostat stuck openCommon
- Thermostat stuck closedPossible
Parts involved
- Transmission Fluid Thermostat
- Transmission Cooler
P07CB is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.