2015 Hyundai Santa Fe P1800 Code and Harsh Shifting

Question

My Santa Fe started shifting really hard between 2nd and 3rd gear, and the check engine light came on yesterday. I scanned it and got code P1800 which is related to the Transmission Fluid Temperature sensor. It seems to drive okay when cold but gets worse once the engine reaches operating temp.

torque_terry · Accepted Answer

The issue was definitely the internal transmission oil temperature sensor and the ribbon cable harness. I replaced the sensor (Part #46386-3B000) and the internal wiring harness. You have to drop the plastic oil pan/cover on the front of the transmission to get to it. Total cost for parts was about $95 and it required 5 quarts of SP-IV fluid to refill. Shifting is back to factory smooth now.

obd2_owl · Answer

Is the TCM software up to date? I recall a TSB regarding shift logic and temperature sensor plausibility for the 2014-2016 models. A dealer flash might be cheaper than a hardware swap.

Sam Holloway · Answer

On these Hyundai 6-speed units, the internal wiring harness for the TFT sensor is notorious for failing. Check the resistance at the sensor pins if you have a multimeter; it should change smoothly as the temperature rises.

Dave Kowalski · Answer

Sometimes P1800 can be triggered by a bad ground or a failing battery causing voltage drops to the TCM. Make sure your charging system is putting out at least 13.8V before you tear into the trans.

2015 Hyundai Santa Fe P1800 Code and Harsh Shifting

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