DTC 74 - P1799

Name of Code:
P-1799(74) - Calculated Oil Temperature in Use

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 Transmission Temperature Sensor voltage is out of range (below 0.07 volts or greater than 4.94 volts)
- If continuous erratic Transmission Temperature Sensor voltage is sensed.
- The Transmission Temperature Sensor temperature stays below 80° for an extended period of time.

Theory of Operation: The TCM uses a Transmission Temperature Sensor to monitor the transmission's sump temperature. This temperature is used to determine which shift schedule the TCM is to use. (See "Transmission Operation and Shift Scheduling at Various Sump Temperatures") If the Transmission 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 Transmission Temperature Sensor circuit after ever 35 OBDII warm-up starts. If the Transmission Temperature Sensor circuit is OK, the Transmission Temperature Sensor data is used in place of the Calculated Oil temperature data.

Transmission Effects: If the Transmission Temperature Sensor indicates a temperature below O° or above 240° at start up, The TCM compares the calculated oil temperature to the indicated Transmission Temperature Sensor oil temperature. If the calculated oil temperature differs significantly from the Transmission Temperature Sensor value, the calculated oil temperature will be used for that key start.

Possible Causes:
- Wiring or Connector problems in the transmission temperature sensor signal circuit.
- Defective TRS
- Defective TCM