P1479A Transmission Fan Relay Circuit

1999

NAME OF TEST
Inoperative Transmission Cooling Fan

THEORY OF OPERATION
The Powertrain Control Module (PCM), controls the transmission cooling fan. The transmission temperature is a bussed message from the Transmission Control Module (TCM) to the PCM. The transmission cooling fan will turn ON at 206 degrees Fahrenheit and will turn OFF at 200 degrees Fahrenheit, when the engine cooling fan is off. If the engine cooling fan is on, the transmission cooling fan will turn ON at 192 degrees Fahrenheit and will turn OFF only when the engine cooling fan turns off.

The PCM will default and turn the transmission cooling fan on, if no transmission temperature is received on the buss communication line, from the TCM.

POSSIBLE CAUSES
- Fuse or Fused B+ is open
- Open ground circuit to the transmission cooling fan motor
- Connector terminals
- Connector wires
- Shorted or Open relay coil
- Shorted or Open relay contacts
- Inoperative temperature sensor
- Shorted or Open transmission cooling fan motor
- No bussed messages from the Transmission Control Module
- Inoperative control circuit in Powertrain Control Module