What it means
The TCM/PCM detected that automatic transmission fluid temperature exceeded the safe operating threshold. Continued operation accelerates wear on clutches and friction surfaces; many vehicles will engage a fail-safe mode and limit gear selection.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The transmission fluid cools and lubricates an automatic transmission, while the TCM or PCM monitors its temperature. P0218 sets when measured transmission-fluid temperature exceeds the safe operating threshold; continued overheating can damage clutches and friction surfaces, and some vehicles limit gear selection.
Common causes
Most likely first.
- Low or degraded transmission fluid
- Transmission cooler blocked or restricted
- Sustained heavy load or towing
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 live transmission-fluid temperature, noting vehicle speed, load, and whether the vehicle was towing.
- Check for related transmission codes and note any fail-safe mode, slipping, shuddering, or delayed shifts.
- Inspect for transmission-fluid leaks and check the fluid level and condition using the vehicle manufacturer's procedure.
- Inspect the transmission cooler and its lines for damage, blockage, or restricted airflow.
- If the fluid level and cooler appear sound, have the temperature reading and transmission operation checked against the manufacturer's diagnostic procedure.
Common fixes
- Correct a low fluid level only after identifying and repairing the leak.
- Replace degraded fluid using the manufacturer's specified procedure and fluid.
- Repair damaged or restricted cooler lines.
- Clean or repair a blocked transmission cooler or its airflow path.
- Repair a confirmed transmission temperature-sensor or internal transmission fault.
Can I keep driving?
Avoid towing, steep climbs, and other heavy loads, and stop if the transmission warning remains on or shifting becomes abnormal. Continued operation while hot can accelerate transmission damage; use recovery if it slips or loses drive.
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.