P0218

P0218 indicates the transmission control module has measured automatic transmission fluid temperature above the calibrated threshold (typically 270 to 300 F depending on manufacturer), which forces a limp-in strategy to protect the clutches and valve body. Start with the cheapest checks: confirm ATF level and condition on a level surface at operating temperature (cold-bright cherry red is ideal; brown or burnt-smelling fluid has lost its friction modifiers and oxidized), inspect the transmission cooler lines for kinks or restrictions, and verify the radiator cooler tank is not internally blocked by debris. Live-data with a scan tool: monitor TFT (transmission fluid temperature) sensor at key-on cold soak — it should read within 5 F of ambient and within 5 F of ECT; resistance of a typical NTC TFT sensor is roughly 3.0 kohm at 70 F and drops to about 100 to 300 ohm at 250 F. If TFT tracks ECT and both rise abnormally during light load, the problem is cooling-system or load-related, not sensor. Caveat: a stuck-open thermostat or low coolant raises TFT indirectly through the cooler-in-radiator path, so chasing the trans before fixing engine cooling wastes labor.

Vehicle-specific patterns: 2004-2010 Ford F-150 5.4L (4R75E/6R80) — towing above GCWR with the factory cooler routes ATF through a radiator tank that silts up; aftermarket auxiliary cooler plus full fluid exchange is the standard fix. 2007-2013 GMC Sierra/Chevy Silverado 6L80 — TEHCM internal solenoid wear raises line pressure and heat; GM bulletin PIP4811 covers reflash plus solenoid pack. 2003-2009 Dodge Ram 1500 (45RFE/545RFE) — degraded ATF+4 past 60k miles loses viscosity and overheats on grade; pan-drop plus filter is inadequate, full exchange required. 2006-2012 Toyota Tundra 5.7L (AB60) — trailer-tow without the OEM tow package overwhelms the cooler; retrofit of the tow-package cooler resolves recurrence. Estimated repair: $180 to $1400.