P1799 (74) - Calculated Oil Temperature In Use

Name of Code:
P1799 (74) - Temperature Sensor

When Monitored:
Whenever the Engine is running.

Set Condition:
The code is set if any of the following conditions exist for three consecutive key starts:
- The Temperature Sensor voltage is out of range (below 0.07 volts or greater than 4.94 volts).
- If continuous erratic Temperature Sensor voltage is sensed.
- The Temperature Sensor temperature stays below 80°F for an extended period of time.

Theory of Operation:
The TCM uses a Temperature Sensor to monitor the transmission's sump temperature. This temperature is used to determine which shift schedule the TCM is to use. If the Temperature Sensor circuit fails to operate properly the TCM will use the calculated oil temperature routine found in prior model year TCM's. If this occurs for three consecutive key starts, the code will be set. The TCM will then test the Temperature Sensor circuit after every 35TH OBDII warm-up start. If the Temperature Sensor circuit is OK, the Temperature Sensor data is used in place of the Calculated Oil Temperature Routine.

Transmission Effects:
If the Temperature Sensor indicates a temperature below 0°F or above 240°F at start up, the TCM compares the calculated oil temperature to the indicated oil temperature. If the calculated oil temperature differs significantly from the Temperature Sensor value, the calculated oil temperature will be used for that key start. This code does not cause the transmission to go into limp-in mode.

Possible Causes:
- Transmission temperature sensor signal circuit short to ground, short to voltage, or open circuit.
- Speed sensor ground circuit short to ground, short to voltage, or open circuit.
- Temperature Sensor
- TCM