DTC 79

Circuit Trans Fluid Overtemp:

CIRCUIT DESCRIPTION
The Trans Fluid Temperature (TFT) sensor is a 2 wire thermistor located in the transaxle. This sensor operates in the same way as an Engine Coolant Temperature (ECT) or Intake Air Temperature (IAT) sensor. 5 volts is applied to the sensor on CKT 1227 by the Powertrain Control Module (PCM). The voltage sensed at PCM pin "A32" will be high when the trans fluid is cold, and as the transaxle fluid warms the signal voltage will drop. A very low signal voltage therefore indicates a high fluid temperature. If the transaxle is driven under harsh conditions for an extended period, a Diagnostic Trouble Code (DTC) 79 will set to alert the driver of a transaxle over temperature condition. A trans fluid check should be made any time this DTC is stored.

DTC 79 Will Set When: No current DTC 58 or 59 is set and trans fluid temp is between 120°C and 130°C for 5 seconds.

Action Taken (PCM will default to): Torque Converter Clutch (TCC) will become engaged, in 2nd, 3rd or 4th gears to help cool the trans fluid. Shift patterns will change to best enable cooler transaxle operation. The Malfunction Indicator Lamp (MIL) will not become illuminated.

DTC 79 Will Clear When: A current DTC 79 will clear when the TFT senses fluid temperature has fallen below 120°C. A History DTC 79 will clear after 50 consecutive ignition key cycles without a current DTC 79 being stored.

TEST DESCRIPTION
DTC 79 indicates a transmission fluid over-temperature condition has occurred. The PCM determines if the TFT temperature is accurate by checking for gross failures of the TFT sensor first (DTC 58, 59). When valid data is established, a DTC 79 will be set if the TFT sensor indicates above 130°C and will clear from current DTC when the temperature falls below 120°C. Check for possible conditions that would cause a transmission over-temperature condition. Driving conditions like: Trailer towing, Steep grades, etc.. should not be discounted. Check fluid level.