What does it mean?
P1808 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: TC-SST-ECU temperature, fluid temperature sensor system (Correlation error) .
Symptoms
- MIL (check engine lamp) is on, often with a transmission overheat warning on the display
- Clutch protection engages: torque is reduced and the vehicle feels flat under hard driving
- Jerky launches and rough gear changes once the transmission is hot
- A message asking the driver to stop and let the transmission cool
- The fault clears after the vehicle cools and returns after a period of demanding driving
- Transmission may refuse to engage a gear until it cools
Likely causes
- Transmission fluid temperature sensor drifted, failed or reading with an offset
- High-resistance joint or corroded connector in the sensor circuit, shifting the reading
- Genuinely overheated clutch packs from heavy stop-start use, towing or repeated hard launches
- Low fluid level or degraded fluid, so heat is not carried away from the clutches
- Blocked or restricted transmission cooler, or a failed cooler fan or pump
- Internal temperature sensor in the control unit faulty
- Outdated control unit software with an incorrect correlation strategy
How to fix it
- With the vehicle fully cold, read both the fluid temperature and the control unit temperature in live data; a large gap confirms one of them is wrong
- Check the fluid level and condition and service it with the correct specification and exact quantity
- Inspect the transmission cooler, its lines and any cooling fan or pump for blockage and correct operation
- Inspect the sensor connector and wiring for corrosion and a high-resistance joint, and measure sensor resistance against the temperature table
- Check whether updated control unit software is available and apply it if so
- Replace the fluid temperature sensor if it stays out of correlation; if the temperatures are genuinely excessive, investigate clutch wear and driving conditions