What it means
The transmission control module monitors transmission fluid temperature behavior to assess thermostat operation. It sets this code when the temperature response does not match the expected performance of the fluid thermostat.
At a glance
- Usually lights the check-engine light
How it works
The transmission fluid thermostat regulates fluid flow to help the transmission warm up and operate within its intended temperature range. The transmission control module compares fluid-temperature behavior with expected warm-up or operating behavior and sets P07CB when that response suggests the thermostat is stuck open or stuck closed.
Common causes
Most likely first.
- Thermostat stuck open
- Thermostat stuck closed
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
How to diagnose it
- Record freeze-frame data and review transmission fluid temperature from a cold start through warm-up to see how its rise compares with engine temperature and driving conditions.
- Check for related temperature-sensor or transmission codes that could make the thermostat response appear abnormal.
- Inspect the thermostat area and accessible transmission-fluid cooling lines for damage, leaks, or signs of restricted or abnormal flow.
- Use vehicle service information to confirm the thermostat circuit and temperature sensor readings are plausible before condemning the thermostat.
- If the readings support a thermostat fault, test its operation or removal condition according to the manufacturer's procedure.
Common fixes
- Repair a damaged or disconnected transmission temperature sensor connector or wiring if it is distorting temperature data.
- Correct an identified transmission-fluid cooling line restriction or leak.
- Replace a thermostat confirmed stuck open or stuck closed.
- Restore the specified transmission fluid level and condition if inspection finds a related issue.
Can I keep driving?
A warning light alone may allow a cautious trip, but stop if the transmission overheats, slips, or shifts abnormally. Avoid towing and heavy loads until diagnosed, since incorrect fluid temperature control can accelerate wear or lead to overheating.
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.