P0218 Code: Transmission Fluid Over Temperature Condition
The transmission fluid got hotter than the computer allows, from heavy load, low fluid or a cooling problem.
Stop driving
Pull over when it's safe and let the engine idle in Park for a few minutes with the A/C off so the pump keeps fluid moving through the cooler. If you smell burning fluid or see smoke, shut it off. Don't resume towing or climbing until the temperature is normal and the cause is known.
Safety first · Consult a professional
- Fire risk: stop driving if you smell burning or see smoke.
At a glance
Severity: High
- Meaning
- Transmission Fluid Over Temperature Condition
- System
- Transmission · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $150–$5,500
- DIY difficulty
- Moderate
P0218 is not a sensor circuit code: the transmission fluid temperature (TFT) signal was electrically valid, but it climbed past the limit the powertrain computer accepts. Most automatics are happiest around 175 to 200°F; the over-temperature threshold is usually somewhere in the 250 to 300°F range depending on the manufacturer, and there the fluid oxidizes quickly while clutch linings and seals start to suffer. To protect itself, the transmission may lock the converter earlier, change shift timing, show a temperature warning or cut power. Common triggers are towing or crawling in heat, low or worn-out fluid, a clogged cooler, a slipping converter clutch, or an engine cooling problem that heats the cooler inside the radiator.
How to read P0218
- P Powertrain
- 0 Generic (SAE)
- 2 Fuel & air (injector circuit)
- 18 Specific fault
Symptoms
- Transmission temperature warning or message on the dash
- Firm or late shifts, or the converter locking up earlier than usual as the computer protects itself
- Burnt smell, or fluid spitting from the dipstick tube or vent
- Limp mode with reduced power or a single gear on some models
- Problem appears only when towing, in stop-and-go heat or on long grades
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Heavy towing or hauling, long climbs or low-speed off-road driving in hot weather
- Low fluid level, or old fluid that has oxidized and lost its cooling ability
- Transmission cooler or lines blocked by debris or internal sludge, or an auxiliary cooler bypassed
- Torque converter clutch slipping or not applying, turning engine power into heat
- Engine cooling problem (fan, thermostat, low coolant) overheating the cooler inside the radiator
- TFT sensor or internal harness reporting a falsely high temperature
Diagnosis step by step
Watch live TFT against coolant temperature
In scan data, compare transmission fluid temperature with engine coolant after a normal drive. TFT usually settles near or slightly above coolant, around 175 to 200°F. A value far above coolant on an easy drive, or a sudden jump, needs explaining.
Tools: OBD-II scanner
Confirm with an infrared thermometer
Right after the warning, aim at the transmission pan and the cooler lines. If the pan reads dramatically cooler than the scan tool claims, suspect the TFT sensor or internal harness. If the pan is genuinely very hot, the heat is real.
Tools: Flashlight
Check fluid level and condition the right way
Many newer automatics have no dipstick and must be checked through a fill or check plug at a specified fluid temperature. Dark brown fluid with a burnt smell or visible friction material means the heat has already caused wear.
Tools: OBD-II scanner, Gloves
Compare cooler inlet and outlet
With everything warm, measure the lines going into and coming out of the cooler. A working cooler shows a clear temperature drop, especially at highway speed; almost no difference points to a blocked cooler, a restricted line or a stuck bypass.
Tools: Gloves
Check torque converter slip
At a steady 50 to 60 mph with lockup commanded, watch TCC slip (or engine rpm against input or turbine speed). Slip should be close to zero, typically under about 50 rpm. Hundreds of rpm with lockup commanded means the converter clutch is generating the heat.
Tools: OBD-II scanner
Rule out engine cooling
If coolant temperature is also high or the electric fan isn't cycling, fix that first. On most vehicles the transmission cooler sits in the radiator tank, so an overheating engine drags the transmission along with it.
Tools: OBD-II scanner, Flashlight
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Fluid and filter service with the specified fluid | No | $150–$450 |
| Add auxiliary transmission cooler for towing | Yes | $150–$500 |
| Flush or replace transmission cooler and lines | No | $200–$700 |
| Replace TFT sensor or internal harness | No | $250–$700 |
| Replace torque converter or rebuild heat-damaged transmission | No | $900–$5,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Dodge | 2 | Caliber, Dakota | |
|---|---|---|---|
| Jeep | 2 | Patriot, Wrangler |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Depends
Whether P0218 turns on the check engine light depends on the vehicle; some only show a transmission warning. If the check engine light is on at the test, an OBD-II smog check fails; a stored code without the light usually does not.
Frequently asked questions
How hot is too hot for transmission fluid?
Most fluids live happily around 175 to 200°F. A widely used rule of thumb says fluid life roughly halves for every 20°F above that range, and sustained temperatures past about 250°F quickly harden seals and varnish the valve body.
Will an auxiliary cooler fix P0218?
If the cause is towing or hot-weather driving, a properly sized auxiliary cooler usually does. If the converter slips or the fluid is low, a bigger cooler just hides the problem while wear continues.
Do I need to change the fluid after it overheated?
Check it. If it smells burnt or has darkened noticeably, change it with exactly the specified fluid; a single hot episode can oxidize fluid enough to affect shift quality.
Could the temperature sensor be lying?
Sometimes. Compare the scan reading with an infrared reading on the pan. On many transmissions the TFT sensor is part of the internal harness or solenoid assembly, so replacing it means dropping the pan.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy